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  Subjects -> ELECTRONICS (Total: 207 journals)
Showing 1 - 200 of 277 Journals sorted alphabetically
Acta Electronica Malaysia     Open Access  
Advanced Materials Technologies     Hybrid Journal   (Followers: 1)
Advances in Biosensors and Bioelectronics     Open Access   (Followers: 8)
Advances in Electrical and Electronic Engineering     Open Access   (Followers: 9)
Advances in Electronics     Open Access   (Followers: 100)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 8)
Advances in Microelectronic Engineering     Open Access   (Followers: 13)
Advances in Power Electronics     Open Access   (Followers: 40)
Advancing Microelectronics     Hybrid Journal  
American Journal of Electrical and Electronic Engineering     Open Access   (Followers: 28)
Annals of Telecommunications     Hybrid Journal   (Followers: 8)
APSIPA Transactions on Signal and Information Processing     Open Access   (Followers: 9)
Archives of Electrical Engineering     Open Access   (Followers: 16)
Australian Journal of Electrical and Electronics Engineering     Hybrid Journal  
Batteries     Open Access   (Followers: 9)
Batteries & Supercaps     Hybrid Journal   (Followers: 5)
Bell Labs Technical Journal     Hybrid Journal   (Followers: 31)
Bioelectronics in Medicine     Hybrid Journal  
Biomedical Instrumentation & Technology     Hybrid Journal   (Followers: 6)
BULLETIN of National Technical University of Ukraine. Series RADIOTECHNIQUE. RADIOAPPARATUS BUILDING     Open Access   (Followers: 2)
Bulletin of the Polish Academy of Sciences : Technical Sciences     Open Access   (Followers: 1)
Canadian Journal of Remote Sensing     Full-text available via subscription   (Followers: 47)
China Communications     Full-text available via subscription   (Followers: 9)
Chinese Journal of Electronics     Hybrid Journal  
Circuits and Systems     Open Access   (Followers: 15)
Consumer Electronics Times     Open Access   (Followers: 5)
Control Systems     Hybrid Journal   (Followers: 309)
ECTI Transactions on Computer and Information Technology (ECTI-CIT)     Open Access  
ECTI Transactions on Electrical Engineering, Electronics, and Communications     Open Access   (Followers: 2)
Edu Elektrika Journal     Open Access   (Followers: 1)
Electrica     Open Access  
Electronic Design     Partially Free   (Followers: 124)
Electronic Markets     Hybrid Journal   (Followers: 7)
Electronic Materials Letters     Hybrid Journal   (Followers: 4)
Electronics     Open Access   (Followers: 109)
Electronics and Communications in Japan     Hybrid Journal   (Followers: 10)
Electronics For You     Partially Free   (Followers: 103)
Electronics Letters     Hybrid Journal   (Followers: 26)
Elektronika ir Elektortechnika     Open Access   (Followers: 2)
Elkha : Jurnal Teknik Elektro     Open Access  
Emitor : Jurnal Teknik Elektro     Open Access   (Followers: 3)
Energy Harvesting and Systems     Hybrid Journal   (Followers: 4)
Energy Storage     Hybrid Journal   (Followers: 1)
Energy Storage Materials     Full-text available via subscription   (Followers: 4)
EPE Journal : European Power Electronics and Drives     Hybrid Journal  
EPJ Quantum Technology     Open Access   (Followers: 1)
EURASIP Journal on Embedded Systems     Open Access   (Followers: 11)
Facta Universitatis, Series : Electronics and Energetics     Open Access  
Foundations and Trends® in Communications and Information Theory     Full-text available via subscription   (Followers: 6)
Foundations and Trends® in Signal Processing     Full-text available via subscription   (Followers: 9)
Frequenz     Hybrid Journal   (Followers: 1)
Frontiers of Optoelectronics     Hybrid Journal   (Followers: 1)
IACR Transactions on Symmetric Cryptology     Open Access   (Followers: 1)
IEEE Antennas and Propagation Magazine     Hybrid Journal   (Followers: 102)
IEEE Antennas and Wireless Propagation Letters     Hybrid Journal   (Followers: 81)
IEEE Embedded Systems Letters     Hybrid Journal   (Followers: 57)
IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology     Hybrid Journal   (Followers: 3)
IEEE Journal of Emerging and Selected Topics in Power Electronics     Hybrid Journal   (Followers: 52)
IEEE Journal of the Electron Devices Society     Open Access   (Followers: 9)
IEEE Journal on Exploratory Solid-State Computational Devices and Circuits     Hybrid Journal   (Followers: 1)
IEEE Letters on Electromagnetic Compatibility Practice and Applications     Hybrid Journal   (Followers: 4)
IEEE Magnetics Letters     Hybrid Journal   (Followers: 7)
IEEE Nanotechnology Magazine     Hybrid Journal   (Followers: 42)
IEEE Open Journal of Circuits and Systems     Open Access   (Followers: 3)
IEEE Open Journal of Industry Applications     Open Access   (Followers: 3)
IEEE Open Journal of the Industrial Electronics Society     Open Access   (Followers: 3)
IEEE Power Electronics Magazine     Full-text available via subscription   (Followers: 77)
IEEE Pulse     Hybrid Journal   (Followers: 5)
IEEE Reviews in Biomedical Engineering     Hybrid Journal   (Followers: 23)
IEEE Solid-State Circuits Letters     Hybrid Journal   (Followers: 3)
IEEE Solid-State Circuits Magazine     Hybrid Journal   (Followers: 13)
IEEE Transactions on Aerospace and Electronic Systems     Hybrid Journal   (Followers: 367)
IEEE Transactions on Antennas and Propagation     Full-text available via subscription   (Followers: 74)
IEEE Transactions on Automatic Control     Hybrid Journal   (Followers: 64)
IEEE Transactions on Autonomous Mental Development     Hybrid Journal   (Followers: 8)
IEEE Transactions on Biomedical Engineering     Hybrid Journal   (Followers: 39)
IEEE Transactions on Broadcasting     Hybrid Journal   (Followers: 13)
IEEE Transactions on Circuits and Systems for Video Technology     Hybrid Journal   (Followers: 26)
IEEE Transactions on Consumer Electronics     Hybrid Journal   (Followers: 46)
IEEE Transactions on Electron Devices     Hybrid Journal   (Followers: 19)
IEEE Transactions on Geoscience and Remote Sensing     Hybrid Journal   (Followers: 227)
IEEE Transactions on Haptics     Hybrid Journal   (Followers: 5)
IEEE Transactions on Industrial Electronics     Hybrid Journal   (Followers: 75)
IEEE Transactions on Industry Applications     Hybrid Journal   (Followers: 40)
IEEE Transactions on Information Theory     Hybrid Journal   (Followers: 27)
IEEE Transactions on Learning Technologies     Full-text available via subscription   (Followers: 12)
IEEE Transactions on Power Electronics     Hybrid Journal   (Followers: 80)
IEEE Transactions on Services Computing     Hybrid Journal   (Followers: 4)
IEEE Transactions on Signal and Information Processing over Networks     Hybrid Journal   (Followers: 13)
IEEE Transactions on Software Engineering     Hybrid Journal   (Followers: 79)
IEEE Women in Engineering Magazine     Hybrid Journal   (Followers: 11)
IEEE/OSA Journal of Optical Communications and Networking     Hybrid Journal   (Followers: 16)
IEICE - Transactions on Electronics     Full-text available via subscription   (Followers: 12)
IEICE - Transactions on Information and Systems     Full-text available via subscription   (Followers: 5)
IET Cyber-Physical Systems : Theory & Applications     Open Access   (Followers: 1)
IET Energy Systems Integration     Open Access   (Followers: 1)
IET Microwaves, Antennas & Propagation     Hybrid Journal   (Followers: 36)
IET Nanodielectrics     Open Access  
IET Power Electronics     Hybrid Journal   (Followers: 60)
IET Smart Grid     Open Access   (Followers: 1)
IET Wireless Sensor Systems     Hybrid Journal   (Followers: 18)
IETE Journal of Education     Open Access   (Followers: 4)
IETE Journal of Research     Open Access   (Followers: 11)
IETE Technical Review     Open Access   (Followers: 13)
IJEIS (Indonesian Journal of Electronics and Instrumentation Systems)     Open Access   (Followers: 3)
Industrial Technology Research Journal Phranakhon Rajabhat University     Open Access  
Informatik-Spektrum     Hybrid Journal   (Followers: 2)
Instabilities in Silicon Devices     Full-text available via subscription   (Followers: 1)
Intelligent Transportation Systems Magazine, IEEE     Full-text available via subscription   (Followers: 14)
International Journal of Advanced Research in Computer Science and Electronics Engineering     Open Access   (Followers: 18)
International Journal of Advances in Telecommunications, Electrotechnics, Signals and Systems     Open Access   (Followers: 12)
International Journal of Antennas and Propagation     Open Access   (Followers: 11)
International Journal of Applied Electronics in Physics & Robotics     Open Access   (Followers: 4)
International Journal of Computational Vision and Robotics     Hybrid Journal   (Followers: 5)
International Journal of Control     Hybrid Journal   (Followers: 11)
International Journal of Electronics     Hybrid Journal   (Followers: 7)
International Journal of Electronics and Telecommunications     Open Access   (Followers: 13)
International Journal of Granular Computing, Rough Sets and Intelligent Systems     Hybrid Journal   (Followers: 3)
International Journal of High Speed Electronics and Systems     Hybrid Journal  
International Journal of Hybrid Intelligence     Hybrid Journal  
International Journal of Image, Graphics and Signal Processing     Open Access   (Followers: 16)
International Journal of Microwave and Wireless Technologies     Hybrid Journal   (Followers: 10)
International Journal of Nanoscience     Hybrid Journal   (Followers: 1)
International Journal of Numerical Modelling: Electronic Networks, Devices and Fields     Hybrid Journal   (Followers: 4)
International Journal of Power Electronics     Hybrid Journal   (Followers: 25)
International Journal of Review in Electronics & Communication Engineering     Open Access   (Followers: 4)
International Journal of Sensors, Wireless Communications and Control     Hybrid Journal   (Followers: 10)
International Journal of Systems, Control and Communications     Hybrid Journal   (Followers: 4)
International Journal of Wireless and Microwave Technologies     Open Access   (Followers: 6)
International Transaction of Electrical and Computer Engineers System     Open Access   (Followers: 2)
JAREE (Journal on Advanced Research in Electrical Engineering)     Open Access  
Journal of Biosensors & Bioelectronics     Open Access   (Followers: 4)
Journal of Advanced Dielectrics     Open Access   (Followers: 1)
Journal of Artificial Intelligence     Open Access   (Followers: 12)
Journal of Circuits, Systems, and Computers     Hybrid Journal   (Followers: 4)
Journal of Computational Intelligence and Electronic Systems     Full-text available via subscription   (Followers: 1)
Journal of Electrical and Electronics Engineering Research     Open Access   (Followers: 38)
Journal of Electrical Bioimpedance     Open Access  
Journal of Electrical Bioimpedance     Open Access   (Followers: 2)
Journal of Electrical Engineering & Electronic Technology     Hybrid Journal   (Followers: 7)
Journal of Electrical, Electronics and Informatics     Open Access  
Journal of Electromagnetic Analysis and Applications     Open Access   (Followers: 8)
Journal of Electromagnetic Waves and Applications     Hybrid Journal   (Followers: 9)
Journal of Electronic Design Technology     Full-text available via subscription   (Followers: 6)
Journal of Electronic Science and Technology     Open Access   (Followers: 1)
Journal of Electronics (China)     Hybrid Journal   (Followers: 5)
Journal of Energy Storage     Full-text available via subscription   (Followers: 4)
Journal of Engineered Fibers and Fabrics     Open Access   (Followers: 2)
Journal of Field Robotics     Hybrid Journal   (Followers: 4)
Journal of Guidance, Control, and Dynamics     Hybrid Journal   (Followers: 189)
Journal of Information and Telecommunication     Open Access   (Followers: 1)
Journal of Intelligent Procedures in Electrical Technology     Open Access   (Followers: 3)
Journal of Low Power Electronics     Full-text available via subscription   (Followers: 10)
Journal of Low Power Electronics and Applications     Open Access   (Followers: 10)
Journal of Microelectronics and Electronic Packaging     Hybrid Journal   (Followers: 1)
Journal of Microwave Power and Electromagnetic Energy     Hybrid Journal   (Followers: 3)
Journal of Microwaves, Optoelectronics and Electromagnetic Applications     Open Access   (Followers: 11)
Journal of Nuclear Cardiology     Hybrid Journal  
Journal of Optoelectronics Engineering     Open Access   (Followers: 4)
Journal of Physics B: Atomic, Molecular and Optical Physics     Hybrid Journal   (Followers: 32)
Journal of Power Electronics     Hybrid Journal   (Followers: 2)
Journal of Power Electronics & Power Systems     Full-text available via subscription   (Followers: 11)
Journal of Semiconductors     Full-text available via subscription   (Followers: 5)
Journal of Sensors     Open Access   (Followers: 27)
Journal of Signal and Information Processing     Open Access   (Followers: 8)
Jurnal ELTIKOM : Jurnal Teknik Elektro, Teknologi Informasi dan Komputer     Open Access  
Jurnal Rekayasa Elektrika     Open Access  
Jurnal Teknik Elektro     Open Access  
Jurnal Teknologi Elektro     Open Access  
Kinetik : Game Technology, Information System, Computer Network, Computing, Electronics, and Control     Open Access  
Majalah Ilmiah Teknologi Elektro : Journal of Electrical Technology     Open Access   (Followers: 2)
Metrology and Measurement Systems     Open Access   (Followers: 6)
Microelectronics and Solid State Electronics     Open Access   (Followers: 28)
Nanotechnology, Science and Applications     Open Access   (Followers: 6)
Nature Electronics     Hybrid Journal   (Followers: 1)
Networks: an International Journal     Hybrid Journal   (Followers: 5)
Open Electrical & Electronic Engineering Journal     Open Access  
Open Journal of Antennas and Propagation     Open Access   (Followers: 8)
Paladyn. Journal of Behavioral Robotics     Open Access   (Followers: 1)
Power Electronics and Drives     Open Access   (Followers: 2)
Problemy Peredachi Informatsii     Full-text available via subscription  
Progress in Quantum Electronics     Full-text available via subscription   (Followers: 7)
Radiophysics and Quantum Electronics     Hybrid Journal   (Followers: 2)
Recent Advances in Communications and Networking Technology     Hybrid Journal   (Followers: 3)
Recent Advances in Electrical & Electronic Engineering     Hybrid Journal   (Followers: 11)
Research & Reviews : Journal of Embedded System & Applications     Full-text available via subscription   (Followers: 6)
Revue Méditerranéenne des Télécommunications     Open Access  
Security and Communication Networks     Hybrid Journal   (Followers: 2)
Selected Topics in Applied Earth Observations and Remote Sensing, IEEE Journal of     Hybrid Journal   (Followers: 57)
Semiconductors and Semimetals     Full-text available via subscription   (Followers: 1)
Sensing and Imaging : An International Journal     Hybrid Journal   (Followers: 2)
Solid State Electronics Letters     Open Access  
Solid-State Electronics     Hybrid Journal   (Followers: 9)
Superconductor Science and Technology     Hybrid Journal   (Followers: 3)
Synthesis Lectures on Power Electronics     Full-text available via subscription   (Followers: 3)
Technical Report Electronics and Computer Engineering     Open Access  
TELE     Open Access  
Telematique     Open Access  
TELKOMNIKA (Telecommunication, Computing, Electronics and Control)     Open Access   (Followers: 9)
Transactions on Cryptographic Hardware and Embedded Systems     Open Access   (Followers: 2)

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Similar Journals
Journal Cover
IEEE Journal of Emerging and Selected Topics in Power Electronics
Journal Prestige (SJR): 1.657
Citation Impact (citeScore): 7
Number of Followers: 52  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 2168-6777 - ISSN (Online) 2168-6785
Published by IEEE Homepage  [229 journals]
  • IEEE Journal of Emerging and Selected Topics in Power Electronics
    • Abstract: Presents a listing of the editorial board, board of governors, current staff, committee members, and/or society editors for this issue of the publication.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • IEEE Power Electronics Society Information
    • Abstract: Presents a listing of the editorial board, board of governors, current staff, committee members, and/or society editors for this issue of the publication.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Guest Editorial: Special Section on Modeling, Topology, and Control of
           Grid-Forming Inverters
    • Authors: Marco Liserre;Xiongfei Wang;
      Pages: 923 - 924
      Abstract: The past years have seen a remarkable growth of inverter-based resources in power grids. Conventionally, the inverter-based resources are controlled as current sources, following the phase of grid voltage, with the assumption that the grid voltage is stiff or slightly affected by the current injected from the inverter. This operation mode is commonly known as the grid-following (GFL) or grid-feeding mode. However, as the share of inverter-based resources increases in power grids, the voltages at the points of connection (PoCs) of inverters are not stiff any longer, and GFL inverters tend to be unstable.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Grid-Forming Inverters: A Critical Asset for the Power Grid
    • Authors: Robert H. Lasseter;Zhe Chen;Dinesh Pattabiraman;
      Pages: 925 - 935
      Abstract: Increasing inverter-based sources reduces the system's inertia resulting in possible frequency stability issues. Understanding low-inertia systems and their stability properties is of crucial importance. This article introduces fundamental ways to integrate high levels of renewable energy (RE) and distributed energy resources (DERs) in the power system while creating a more flexible power system. Using RE and DER in the distribution system has many advantages such as reducing the physical and electrical distance between generation and loads, bringing sources closer to loads contributes to the enhancement of the voltage profile, reduction in distribution and transmission bottlenecks, improved reliability, lower losses, and enhances the potential use of waste heat. A basic issue for high penetration of DER is the technical complexity of controlling hundreds of thousands to millions of inverters. This is addressed through autonomous techniques using local measurements eliminating the need for fast control systems. The key issues addressed in this article include using inverter damping to stabilize frequency in systems with low or no inertia, autonomous operation, methods for relieving inverter overload, energy reserves, and their implementation in photovoltaics (PV) systems. This article provides important insight into the interactions between inverter bases sources and the high-power system. The distinction between grid-forming (GFM) inverter and grid-following (GFL) inverter is profound. GFM inverters provide damping to frequency swings in a mixed system, while GFL inverter can aggravate frequency problems with increased penetration. Rather than acting as a source of inertia, the GFM inverter acts as a source of damping to the system. On the other hand, the application of inverters in the power system has two major issues. One is the complexity of controlling hundreds of thousands to millions of inverters. This is addressed through autonomous techniques using local-measurements. The other is the potential of high overcurrent in GFM inverters and techniques for explicitly protecting against overloading. To exploit the innate damping of GFM inverters, energy reserves are critical.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Photovoltaic Synchronous Generator: Architecture and Control Strategy for
           a Grid-Forming PV Energy System
    • Authors: Xiangjun Quan;Ruiyang Yu;Xin Zhao;Yang Lei;Tianxiang Chen;Chengjing Li;Alex Q. Huang;
      Pages: 936 - 948
      Abstract: Transforming a conventional photovoltaic (PV) energy system from a grid-following to a grid-forming system is necessary when PV power generation is dominating the generation mix and for replacing traditional synchronous generators (SGs). The grid-forming PV energy system can provide frequency support functionality, which is vital for the stability of the power grid. This article presents a novel ac coupled solution that transforms an existing grid-following PV system to a grid-forming one without any hardware and software modification of the PV inverter. The resulting system, the PVSG, is achieved by an ac coupled supercapacitor-based energy storage system (ESS). The novel control of the PVSG is implemented in the ESS side. The novel control scheme includes fast and slow instantaneous power controls. The fast-instantaneous power flow control is fulfilled by the dc-link voltage control and ac voltage control. The cascaded voltage source controls enable fast-instantaneous power balance, while a slow instantaneous power control is used to implement inertia and grid synchronization. Two important fundamental functions are realized in the PVSG. The first one is the frequency inertia to resist the grid frequency variation where df/dt-based power control is achieved; the second one is the inertia against the PV intermittent power. The correctness and the effectiveness of the proposed PVSG are experimentally validated in a 480 V PVSG prototype with a TMS320F28379D DSP controller.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • The Role of the Internal Energy in MMCs Operating in Grid-Forming Mode
    • Authors: Enric Sánchez-Sánchez;Eduardo Prieto-Araujo;Oriol Gomis-Bellmunt;
      Pages: 949 - 962
      Abstract: With an increasing number of renewable energy resources being integrated into the power system through power electronics, conventional power plants based on large synchronous machines tend to be reduced in the upcoming future. With the modular multilevel converter (MMC) as the state-of-the-art power electronics solution for power systems, it will be necessary to operate some of these converters in grid-forming mode, in order to either preserve the stability and robustness of the ac grid or as the only solution to generate the ac grid in cases with no available synchronous generation. This article aims to understand how the internal energy control of the MMC can be used to effectively mitigate the propagation of ac power disturbances to the dc side, thanks to its buffering capability. Different energy control structures are explored, and a comprehensive discussion and comparison among them are provided, including stability analysis, transient performance, and tuning guidelines. Simplified and linear models are used to address the analysis, whereas detailed nonlinear models implemented in MATLAB Simulink are used to verify the results via time-domain simulations.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Comparative Study of Two Widely Used Grid-Forming Droop Controls on
           Microgrid Small-Signal Stability
    • Authors: Wei Du;Zhe Chen;Kevin P. Schneider;Robert H. Lasseter;Sai Pushpak Nandanoori;Francis K. Tuffner;Soumya Kundu;
      Pages: 963 - 975
      Abstract: Historically, two similar grid-forming droop controls are widely reported in literature-the single-loop and multi-loop droop controls. Although being very similar, the authors find that the dynamic performance and stability characteristics of each control method are very different in a microgrid. Compared with the single-loop droop control, the multi-loop droop control is prone to be less damped and loses stability more easily under some circumstances. This article provides a novel insight into the different dynamic responses of the two basic controls. It points out that the two similar controls adjust the angular frequency and voltage magnitude at different locations within the inverter, resulting in different coupling reactances that impact the dynamic response and stability of microgrids differently. The use of the single-loop droop control results in a larger coupling reactance, which helps improve the dynamic response and stability. This novel insight is verified through full-order small-signal analysis, offline electromagnetic transient simulation, and real-time hardware-in-the-loop simulation experiments. The results show that the microgrid has a larger small-signal stability boundary when using single-loop droop control, and this difference increases as the value of an inverter's inner filter inductance increases.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Impact of Harmonics and Unbalance on the Dynamics of Grid-Forming,
           Frequency-Droop-Controlled Inverters
    • Authors: Philip J. Hart;Joseph Goldman;Robert H. Lasseter;Thomas M. Jahns;
      Pages: 976 - 990
      Abstract: Due to its multiple advantages, the grid-forming, droop-controlled (GFDC) inverter is a strong contender for large-scale deployment in the future power systems. However, it is still unclear whether higher harmonics can play an important role in the dynamics of GFDC inverter networks. The major objective of this article is to gain insight into whether certain higher harmonics influence or interact with GFDC inverter network dynamics and to characterize this harmonic interaction. For this purpose, a multiple-harmonic dynamic phasor model (DPM) of a representative GFDC network is derived, which can be conveniently extended to hundreds of DPM equations in order to rigorously investigate the effects of dc offsets and/or second-harmonic content, six-step switching harmonics, and unbalance. For a representative network, the results from eigenvalue migration studies show that GFDC dynamics are not strongly influenced by the presence of six-step switching harmonics nor unbalance. For the first time, it is shown that under conditions of high droop slope and high-bandwidth power filtering, dc offsets and second-harmonic content can excite a resonance within the network and even influence the location of the eigenvalues of the linearized DPM. All DPM results are thoroughly validated using Simulink, and the selected results are validated experimentally using the Wisconsin Energy Institute (WEI) microgrid testbed.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Robust Stability Investigation of the Interactions Among Grid-Forming and
           Grid-Following Converters
    • Authors: Roberto Rosso;Soenke Engelken;Marco Liserre;
      Pages: 991 - 1003
      Abstract: State-of-the-art grid-connected converters can be classified as “grid-following,” meaning that they require a dedicated synchronization unit in order to inject active and reactive currents into the grid. Recently, other converter control concepts have been proposed in the literature, such as the synchronverter, which can instead achieve synchronization without a dedicated unit and, within its physical limitations, make the converter behave as an ideal voltage source. Since it should be expected that the grid-connected converters having different control philosophies will coexist for many years, in this article, the interaction among the converters operating nearby are addressed. First, the component connection method (CCM) technique is introduced, as a means for obtaining the state-space representation of a complex system with several units operating nearby. Due to the complexity of the grid and the difficulty in obtaining its exact representation, μ-analysis is adopted in this article for assessing the robust stability of the converter under different operating conditions, according to a defined set of plant uncertainties. Simulation results and experimental tests in a laboratory environment by means of a power hardware-in-the-loop (PHIL) test bench are performed to demonstrate the validity of the presented analysis.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Frequency Stability of Synchronous Machines and Grid-Forming Power
           Converters
    • Authors: Ali Tayyebi;Dominic Groß;Adolfo Anta;Friederich Kupzog;Florian Dörfler;
      Pages: 1004 - 1018
      Abstract: An inevitable consequence of the global power system transition toward nearly 100% renewable-based generation is the loss of conventional bulk generation by synchronous machines (SMs), their inertia, and accompanying frequency- and voltage-control mechanisms. This gradual transformation of the power system to a low-inertia system leads to critical challenges in maintaining system stability. Novel control techniques for converters, so-called grid-forming strategies, are expected to address these challenges and replicate functionalities that, so far, have been provided by SMs. This article presents a low-inertia case study that includes SMs and converters controlled under various grid-forming techniques. In this article, the positive impact of the grid-forming converters (GFCs) on the frequency stability of SMs is highlighted, a qualitative analysis that provides insights into the frequency stability of the system is presented, we explore the behavior of the grid-forming controls when imposing the converter dc and ac current limitations, the importance of the dc dynamics in grid-forming control design as well as the critical need for an effective ac current limitation scheme are reported, and finally, we analyze how and when the interaction between the fast GFC and the slow SM dynamics can contribute to the system instability.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Transient Stability of Voltage-Source Converters With Grid-Forming
           Control: A Design-Oriented Study
    • Authors: Donghua Pan;Xiongfei Wang;Fangcheng Liu;Rongliang Shi;
      Pages: 1019 - 1033
      Abstract: Driven by the large-scale integration of distributed power resources, grid-connected voltage-source converters (VSCs) are increasingly required to operate as grid-forming units to regulate the system voltage/frequency and emulate the inertia. While various grid-forming control schemes have been reported, their transient behaviors under large-signal disturbances are still not fully explored. This article addresses this issue by presenting a design-oriented transient stability analysis of the grid-forming VSCs. First, four typical grid-forming control schemes, namely, the power-synchronization control (PSC), the basic droop control, the droop control with low-pass filters (LPFs), and the virtual synchronous generator (VSG) control, are systematically reviewed, whose dynamics are characterized by a general large-signal model. Based on this model, a comparative analysis on the transient stabilities of different control schemes is then carried out. It reveals that the PSC and the basic droop control can retain a stable operation as long as there are equilibrium points, due to their noninertial transient responses, while the droop control with LPFs and the VSG control can be destabilized even if the equilibrium points exist, due to the lack of damping on their inertial transient responses. With the phase portrait, the underlying stability mechanism is explicitly elaborated, and the quantitative impacts of the controller gains and the virtual inertia are clearly identified. Subsequently, controller design guidelines are proposed to enhance the system damping as well as the transient stability. Finally, experimental results are provided to verify the theoretical analysis.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Mode-Adaptive Power-Angle Control Method for Transient Stability
           Enhancement of Virtual Synchronous Generators
    • Authors: Heng Wu;Xiongfei Wang;
      Pages: 1034 - 1049
      Abstract: The virtual synchronous generator (VSG) is emerging as an attractive solution for interconnecting converter-based resources with the power grid. However, due to the nonlinear power-angle relationship, VSGs are, similar to synchronous generators, prone to the loss of synchronization (LOS) under large grid disturbances. This article, thus, analyzes the large-signal synchronization stability, i.e., the transient stability of grid-connected VSGs, and then proposes a mode-adaptive power-angle control method for enhancing the transient stability. In this approach, the positive-feedback mode of the power-angle control of the VSG is detected and adaptively switched to the negative-feedback mode after large disturbances. Thus, the LOS of the VSG can be avoided when there are equilibrium points after the disturbance. Moreover, during severe grid faults without any equilibrium points, a bounded dynamic response of the power angle can be obtained with the mode-adaptive control, and the VSG can still be stabilized even if the fault-clearing time is beyond the critical clearing time. These superior features prevent the VSG-based system from collapsing due to the delayed fault clearance or the malfunction of protective relays. Finally, the time-domain simulations and experimental tests are performed to verify the effectiveness of the control method.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Critical Clearing Time Determination and Enhancement of Grid-Forming
           Converters Embedding Virtual Impedance as Current Limitation Algorithm
    • Authors: Taoufik Qoria;François Gruson;Fréderic Colas;Guillaume Denis;Thibault Prevost;Xavier Guillaud;
      Pages: 1050 - 1061
      Abstract: This article deals with the postfault synchronization of a voltage source converter based on the droop control. In the case of large disturbances on the grid, the current is limited via current limitation algorithms such as the virtual impedance. During the fault, the power converter internal frequency deviates, resulting in a converter angle divergence. Thereby, the system may lose the synchronism after fault clearing and which may lead to instability. Hence, this article proposes a theoretical approach to explain the dynamic behavior of the grid-forming converter subject to a three-phase bolted fault. A literal expression of the critical clearing time is defined. Due to the precise analysis of the phenomenon, a simple algorithm can be derived to enhance the transient stability. It is based on adaptive gain included in the droop control. These objectives have been achieved with no external information and without switching from one control to the other. To prove the effectiveness of the developed control, experimental test cases have been performed in different faulted conditions.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Current Limiting Control With Enhanced Dynamics of Grid-Forming Converters
           During Fault Conditions
    • Authors: Mads Graungaard Taul;Xiongfei Wang;Pooya Davari;Frede Blaabjerg;
      Pages: 1062 - 1073
      Abstract: With an increasing capacity in the converter-based generation to the modern power system, a growing demand for such systems to be more grid-friendly has emerged. Consequently, grid-forming converters have been proposed as a promising solution as they are compatible with the conventional synchronous-machine-based power system. However, most research focuses on the grid-forming control during normal operating conditions without considering the fundamental distinction between a grid-forming converter and a synchronous machine when considering its short-circuit capability. The current limitation of grid-forming converters during fault conditions is not well described in the available literature and present solutions often aim to switch the control structure to a grid-following structure during the fault. Yet, for a future converter-based power system with no or little integration of synchronous machines, the converters need to preserve their voltage-mode characteristics and be robust toward weak-grid conditions. To address this issue, this article discusses the fundamental issue of grid-forming converter control during grid fault conditions and proposes a fault-mode controller which keeps the voltage-mode characteristics of the grid-forming structure while simultaneously limiting the converter currents to an admissible value. The proposed method is evaluated in a detailed simulation model and verified through an experimental test setup.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Control of Offshore MMC During Asymmetric Offshore AC Faults for Wind
           Power Transmission
    • Authors: Lei Shi;Grain Philip Adam;Rui Li;Lie Xu;
      Pages: 1074 - 1083
      Abstract: The adoptions of medium voltage in ac collection networks of large dc-connected wind farms significantly increase the ac current magnitudes during normal and fault conditions. Controlling fault currents at zero during asymmetric ac faults is possible, but it has several drawbacks such as increased risk of protection mal-operation due to the absence of fault currents, which also tends to prevent the recovery of ac voltage in postfault. Therefore, this paper presents an enhanced control strategy that exploits the induced negative sequence voltages to facilitate controlled injection of negative sequence currents during asymmetric ac faults. The proposed control not only defines a safe level of fault current in the offshore ac network but also instigates immediate recovery of the ac voltage following clearance of ac faults, which avoid protection mal-operation. In addition, the positive sequence voltage set-point of the offshore modular multilevel converter (MMC) is actively controlled by considering the negative and zero sequence voltages, which effectively avoids the excessive overvoltage in the healthy phases during asymmetrical ac faults. The theoretical basis of the proposed control scheme is described and its technical viability is assessed using simulations.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Advanced Current-Limiting and Power-Sharing Control in a PV-Based
           Grid-Forming Inverter Under Unbalanced Grid Conditions
    • Authors: Sara Yazdani;Mehdi Ferdowsi;Masoud Davari;Pourya Shamsi;
      Pages: 1084 - 1096
      Abstract: Grid-forming (GF) inverter technology is a novel and evolving concept for systems with high penetration of renewables. The integration of these grid-independent units with the existing conventional generators and gradually replacing them should contribute to stabilizing the power grid. Several control strategies are proposed in order to design GF inverters to emulate the kinetic energy and the self-synchronization features of synchronous machines with robust control on voltage and frequency to deal with the dynamic issues of the grid. In this article, a photovoltaic (PV)-based GF inverter with a modified virtual synchronous machine control in parallel with a battery supported inverter with an enhanced droop control is considered to operate under non-ideal grid voltage conditions and in the isolated mode of operation. The control methodology encloses a PV synchronous generator, along with the nonlinear feedback linearization current-limiting control with voltage ride-through capabilities. They enable the GF PV inverter and the grid-following battery inverter to provide active and reactive power to the load during unbalanced grid conditions seamlessly. A hardware cosimulation environment in Simulink using the software tool of Piecewise Linear Electrical Circuit Simulation (PLECS) and System Generator from Xilinx is applied to evaluate the operation of the controller and verify its flexibility and effectiveness in different case studies.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Dynamic Microgrids With Self-Organized Grid-Forming Inverters in
           Unbalanced Distribution Feeders
    • Authors: Yuhua Du;Xiaonan Lu;Hao Tu;Jianhui Wang;Srdjan Lukic;
      Pages: 1097 - 1107
      Abstract: In contrast to conventional static microgrids (MGs), MGs with dynamic and adjustable territories (i.e., dynamic MGs) are proposed and implemented in this article. Dynamic MGs are commonly dominated by grid-forming inverters and nested in unbalanced distribution feeders. Unlike balanced systems where only positive-sequence components exist, proper operation of unbalanced dynamic MGs presents additional challenges. A distributed secondary control strategy is developed in this article for distributed generators (DGs) interfaced with grid-forming inverters in unbalanced dynamic MGs by providing coordinated regulations on both positive- and negative-sequence system models. System frequency and voltage are under constant regulation, along with voltage unbalance (VU) management for multiple critical load buses (CLBs). The proposed control strategy enables seamless system transition during unbalanced dynamic MGs reconfiguration and guarantees proportional positive- and negative-sequence power-sharing among connected DGs with respect to system topology variation. Detailed controller designs are provided and stability analyses are derived. The proposed control strategy is fully implemented in hardware controllers and validated on a hardware-in-the-loop (HIL) MG testbed.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Consensus-Based Cooperative Droop Control for Accurate Reactive Power
           Sharing in Islanded AC Microgrid
    • Authors: Jiuyang Zhou;Meng-Jiang Tsai;Po-Tai Cheng;
      Pages: 1108 - 1116
      Abstract: The conventional droop control technology, which can achieve autonomous power sharing among the distributed generation units, suffers from inaccurate reactive power sharing due to its dependence on line impedances. In this article, a novel consensus-based cooperative droop control technique where the droop slope gain is adaptively adjusted is proposed to improve the reactive power-sharing accuracy with the help of a sparse communication network. Through detailed small-signal analysis, it is verified that the proposed droop technique presents excellent immunity against communication delay. Laboratory test results are presented and the performances of the proposed control technique under different operation scenarios are verified, including the load change, communication link failure, and plug-and-play operation.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Modular Multilevel Converter With Self-Voltage Balancing Part I:
           Mathematical Proof
    • Authors: Yunting Liu;Fang Zheng Peng;
      Pages: 1117 - 1125
      Abstract: The modular feature of the modular multilevel converter (MMC) distinguishes itself from other topologies for medium-/high-voltage applications. However, as the count of submodules increases, the control complexity of voltage balancing for each submodule sharply increases. Conventionally, the MMC is deemed to have no inherit voltage balancing property without voltage monitoring and control. This paper mathematically proves that MMC capacitor voltage is self-balanced by nature if considering certain submodule patterns. This implies that MMC could achieve the submodule capacitor voltage balancing without any monitoring or control. The mathematical proof starts from observing the two- and three-level MMCs. Mathematically, two- and three-level MMCs are proved to be self-balanced. Then, a similar observation is extended to N-level MMC. And N-level MMC is proven to be self-balanced mathematically. The modulation which utilizes this MMC merit and secures the self-voltage balancing for MMC will be fully explained in Part II.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Modular Multilevel Converter With Self-Voltage Balancing Part II:
           Y-Matrix Modulation
    • Authors: Yunting Liu;Fang Zheng Peng;
      Pages: 1126 - 1133
      Abstract: In Part I of this paper, the self-voltage balancing nature of modular multilevel converters (MMCs) has been proven mathematically. To utilize this merit of MMCs, a novel modulation, namely Y-matrix modulation (YMM), is proposed to transform the math analysis of Part I into modulation practice. With the proposed YMM, MMCs have secured self-voltage balancing. Conventionally, either a complicated voltage balancing control, or extra components are embedded in MMCs to balance the capacitor voltage. Compared to conventional MMC capacitor voltage balancing strategies, YMM features simple algorithms and good reachability to high-level MMCs while maintaining the original half-bridge submodule topology. To simplify the analysis, YMM is introduced to two-level and three-level MMCs as examples. Then, the generalized YMM is derived, which is suitable for high-level MMCs. Several YMM based MMC case studies are provided for verification purposes.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Bridge-Type Integrated Hybrid DC Circuit Breakers
    • Authors: Sheng Wang;Carlos E. Ugalde-Loo;Chuanyue Li;Jun Liang;Oluwole Daniel Adeuyi;
      Pages: 1134 - 1151
      Abstract: The inclusion of a large number of controllable semiconductor devices in conventional hybrid dc circuit breakers (HCBs) may significantly increase the cost of an HVdc grid protection scheme. In an attempt to reduce this cost, this paper proposes the use of two novel topologies of bridge-type integrated HCBs (BT-ICBs). The two configurations are examined in detail, their operation sequences are established, and a detailed parametric analysis is conducted. The total number of controllable semiconductor devices in a BT-ICB is assessed with the aid of selectivity studies, and a comparison is made when conventional HCB and other ICB topologies are considered. It is shown that the proposed configurations employ 50% to more than 70% less controllable devices compared with conventional HCBs. The proposed BT-ICB topologies are tested in PSCAD/EMTDC using a four-terminal HVdc grid. The simulation results demonstrate the capability and effectiveness of the proposed solutions to isolate different types of dc faults at either a dc line, a converter terminal, or a dc bus.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Harmonic Stability Analysis of MMC-Based DC System Using DC Impedance
           Model
    • Authors: Ke Ji;Guangfu Tang;Jie Yang;Yunfeng Li;Dong Liu;
      Pages: 1152 - 1163
      Abstract: The dc impedance model of a modular multilevel converter (MMC) is the basis for analyzing harmonic resonances of MMC-based dc systems. As an MMC typifies a multiple harmonic response system, its internal dynamics and controls significantly influence its external characteristics. In this paper, a dc impedance model of an MMC is developed by harmonic transfer function method that considers the internal dynamics and typical controls of MMCs. The internal dynamics mainly include capacitor voltage fluctuation and multi-harmonic response characteristics, while typical controls consist of dc voltage control, positive-negative sequence separation-based phase current control, circulating current control, and some other linear controls. As a result, the proposed impedance model can be used not only to analyze the harmonic stability of an MMC-based dc system, but also to investigate the influence of additional controls in an MMC on system stability. Furthermore, the proposed model makes up for the deficiencies in harmonic stability analysis of MMC-based dc systems. The results of both the hardware-in-the-loop RT-LAB digital simulation and the physical experimentation validate the proposed impedance models and analyses.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Stability Analysis of Multi-Port MVDC Distribution Networks for
           All-Electric Ships
    • Authors: Uzair Javaid;Francisco D. Freijedo;Wim van der Merwe;Drazen Dujic;
      Pages: 1164 - 1177
      Abstract: Advances in the power electronics technologies, over the years, have opened up the possibilities to consider medium-voltage dc (MVDC) distribution networks as possible evolutions of the existing medium-voltage ac (MVAC) distribution networks on large ships. The MVDC distribution networks provide the possibilities to increase fuel efficiency and remove bulky transformers. However, to implement industrial-scale MVDC distribution networks, some critical challenges exist, such as lack of standardized equipment and system-level stability. This paper studies the feasibility and stability of MVDC distribution networks when a distributed layout is considered. Due to the nature of the network, a multiple-input-multiple-output (MIMO) impedance stability approach is employed for modeling and assessment. The different components are modeled according to the existing industrial medium-voltage technologies. The theoretical analysis is verified by full-model time-domain simulations. As a summary of the contribution, the main features of the proposed study are: 1) the realistic identification of feasibility limits; 2) the definition of design rules for capacitance sizing and best placement; and 3) the evaluation of distances for dc distribution cables and their corresponding inductances.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Realization of High-Efficiency Dual-Active-Bridge Converter With
           Reconfigurable Multilevel Modulation Scheme
    • Authors: Y. P. Chan;M. Yaqoob;C. S. Wong;K. H. Loo;
      Pages: 1178 - 1192
      Abstract: Efficiency optimization of dual-active-bridge (DAB) converters involves the minimization of both conduction and switching losses. However, it is challenging to achieve these two objectives simultaneously due to their conflicting nature, i.e., circulating current is required to realize zero-voltage switching (ZVS) but the presence of an excessive amount of the circulating current is the main cause of conduction loss and low efficiency. This dilemma has been common to conventional DAB converter topologies and modulation schemes which cannot provide sufficient degrees of freedom (DoFs) to the design of their operation modes. This paper is an illustration of the merits of utilizing reconfigurability of the operation mode as a new DoF in designing the operation of DAB converters to minimize both conduction and switching losses. The proposed DAB converter is designed to switch between two operation modes. For 25%-100% of the rated output power, a new modulation scheme based on the four-level ac voltages is proposed to achieve zero circulating current, zero backflow power, and full-range ZVS. Below 25% of the rated output power, the new modulation scheme transitions smoothly to the enhanced dual-phase-shift (EDPS) modulation scheme that continues to achieve zero backflow power and full-range ZVS while the incurred circulating current is moderated by operating the ac voltages at half-amplitude. The experimental results obtained from a 2-kW prototype show that, in comparison to conventional modulation schemes, the proposed modulation scheme is capable of maintaining the highest efficiency over the full output power range and greatly improves the reliability of switches due to full-range ZVS operation.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Decoupled Stator Resistance Estimation for Speed-Sensorless Induction
           Motor Drives Considering Speed and Load Torque Variations
    • Authors: Cheng Luo;Bo Wang;Yong Yu;Chuang Chen;Zhixin Huo;Dianguo Xu;
      Pages: 1193 - 1207
      Abstract: There are many adaptive full-order observer (AFO)-based simultaneous speed and stator resistance estimation techniques for speed-sensorless induction motor (IM) drives. However, they still need to be improved since the stator resistance estimator is sensitive to speed and load torque variations, especially under low-speed and light-load conditions. In response to this problem, an improved “phase-shift”-based compensation method is proposed for the stator resistance estimation in this paper. Compared with the existing methods, the proposed stator resistance estimation approach is decoupled with the speed estimator by adopting an operating-point-tracking compensation coefficient. Accordingly, the robustness of the stator resistance estimation is guaranteed to speed and load torque variations. The neglected estimated rotor flux error is first introduced for the proposed stator resistance estimator to distinguish the stator resistance error component. Then the sensitivity analysis of the proposed compensation coefficient against parameters variations is carried out. Furthermore, the stability of the speed estimator and the stator resistance estimator is guaranteed owing to the proposed method. The experimental results highlight the effectiveness of the proposed method for improving the accuracy and the stability of the stator resistance estimator under different speeds and load torque conditions.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Lookup Table Model Predictive Direct Torque Control of Permanent-Magnet
           Synchronous Generator Based on Vienna Rectifier
    • Authors: Sook Yee Yip;Hang Seng Che;Chee Pin Tan;Wen Tong Chong;
      Pages: 1208 - 1222
      Abstract: This paper presents the development and implementation of a lookup table model predictive direct torque control (LUT-MPDTC) for a permanent-magnet synchronous generator controlled using a Vienna rectifier. Using a machine model in the stator synchronous reference frame, the feasibility of direct torque control-based model predictive control for the Vienna rectifier is demonstrated. To reduce the computational burden of the MPDTC, a lookup table (LUT) is proposed based on the stator current position and dc-link voltages. The LUT simplifies the complexity of the MPDTC by reducing the number of switching vectors from eight to five, while maintaining the stabilization of the neutral point voltage. The performance and effectiveness of the proposed method are evaluated via MATLAB/Simulink and further validated experimentally using a Texas Instrument-based TMS320F28335 development board. The simulation and experimental results show that the proposed LUT-MPDTC can successfully improve the torque and stator flux ripples as compared to the classical DTC.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Speed Estimation Technique Using Modified Stator Current Error-Based MRAS
           for Direct Torque Controlled Induction Motor Drives
    • Authors: C. Upendra Reddy;Kashyap Kumar Prabhakar;Amit Kumar Singh;Praveen Kumar;
      Pages: 1223 - 1235
      Abstract: This paper uses a stator current error-based model reference adaptive system (MRAS) to estimate the speed of an induction motor drive. Usually, speed error signal uses the cross product of stator current error vector and flux linkage vector for the estimation of speed. However, this speed error signal has limitations, such as speed tracking error and instability (at regenerative mode) under loaded conditions at low speeds. To mitigate these issues, a modified MRAS speed estimation algorithm is proposed in this paper. In the proposed method, the adaptive model state variables are formulated in terms of flux linkages (stator and rotor) in order to alleviate the impact of current noise in the flux linkage estimation. Moreover, a compensator is added to reduce the speed error tracking in the reference model. Furthermore, the stability of the drive is kept by using the dot product of stator current error vector and the rotor flux linkage vector during the regenerative mode of operation. The analysis of the proposed algorithm is presented and validated experimentally on the laboratory setup with direct torque control-space vector modulation technique for a wide operating range including the dynamic performance.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Self-Tuning Control of Advanced Angles for Doubly Salient Motor Drive
           System
    • Authors: Wanying Jia;Lan Xiao;Chuyang Wang;Yangguang Yan;
      Pages: 1236 - 1247
      Abstract: Due to the advantages of simple mechanical structure, high reliability, and high power density, a doubly salient electromagnetic machine (DSEM) has wide application prospects in many areas. Many driving strategies for the DSEM have been developed in recent years, including the standard angle control, the three-state advanced angle control, the six-state advanced angle control, the nine-state advanced angle control, etc. Compared with standard angle control, the driving strategies with advanced angles can further increase the output torque and reduce the torque ripples in the medium/high-speed region. However, the advanced angles are very difficult to select, and the commonly used field-circuit co-simulation method by enumerating advanced angles consumes a lot of time. In addition, once the working condition changes, the advanced angles should be reselected. In this article, self-tuning control of advanced angles based on a several-angle alternating method is proposed, which is carried out by iteratively calculating the advanced angles according to the working conditions. The operating principle of the proposed method is analyzed in detail, together with the change in the pattern of advanced angles and the output characteristics of DSEM. In addition, the implementation method is described, with the upper limitation of advanced angles being selected. Finally, the effectiveness and the feasibility of the proposed method are verified by field-circuit co-simulations and experiments.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Improved Low-Frequency Operation of Hybrid Inverter for Medium-Voltage
           Induction Motor Drive Under V/f and Vector Control Mode of Operation
    • Authors: Archisman Datta;Gautam Poddar;
      Pages: 1248 - 1257
      Abstract: In this paper, an improved control method has been proposed for hybrid inverter to drive medium-voltage induction motor. This hybrid inverter consists of high-voltage three-level inverter that is operated in quasi-square-wave mode. Low-voltage high-frequency H-bridge cells are connected in series with the three-level inverter. They eliminate harmonic voltages generated by the high-voltage quasi-square-wave inverter. This paper proposes systemic choice of harmonic voltages that the series cells need to generate. The choice of these harmonic voltages is dynamically modified based on operating frequency of the drive. This method ensures that the quality of motor current remains same at all operating frequency of the drive. The naturally regulated dc bus voltage of the series cells are kept low for the pulsewidth modulation (PWM) operation of the series cells. Several issues of adopting vector control strategy for hybrid drive have been addressed in this paper. Based on this analysis, suitable motor current control strategy has been proposed without speed sensor. Experimental results are produced for open-loop and closed-loop operations of this drive. The results show the satisfactory operation of this hybrid inverter-based induction motor drive operating from 5 to 50 Hz.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Direct Predictive Speed Control With a Sliding Manifold Term for PMSM
           Drives
    • Authors: Xiaonan Gao;Mohamed Abdelrahem;Christoph M. Hackl;Zhenbin Zhang;Ralph Kennel;
      Pages: 1258 - 1267
      Abstract: This paper proposes a new direct predictive speed control (DPSC) method for permanent-magnet synchronous machines (PMSMs), which eliminates the cascaded loops structure that is usually used in the conventional controller. A novel sliding manifold term is added to the cost function to realize the speed/current tracking. The proposed cost function is simple and easy to implement. Therefore, in comparison with the other DPSC methods, the proposed method does not need long prediction horizons, dynamically adjustable weighting factors or large weighting factors for the control variables with large time constants. The performance of the proposed method has been experimentally investigated and compared with: 1) conventional DPSC scheme and 2) a predictive current control with an outer PI controller (PI-PCC). The results demonstrated enhancement in the dynamic performance in comparison with the PI-PCC method and improvement in the steady-state response in comparison with the conventional DPSC technique.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Performance Enhancement of Evaporative Water Cooler Equipped With
           Permanent Magnet Brushless Motor Drive Based on Power Control Strategy
    • Authors: Abolfazl Halvaei Niasar;Hossein NikKhah;
      Pages: 1268 - 1275
      Abstract: Evaporative coolers with single-phase induction motors (SPIMs) are one of the least efficient and most commonly used electrical power consumers all over the world. Recently, it has been suggested to substitute SPIMs with higher efficiency motors, such as permanent magnet brushless (PMBL) motors. However, control method for brushless motors often works based on speed, while laboratory tests indicate that due to fluid characteristics of the blower, the airflow rate is not just related to the speed, where increasing the cooler's duct length reduces the airflow rate, thereby preventing the desired airflow rate to be reached. To overcome this problem, in this paper, a new power-based control scheme has been developed to stabilize the outlet airflow rate instead of the speed control. In this approach, the output power of PMBL motor is regulated around a set point power corresponding to the desired airflow rate. A 5000-m3/h evaporative cooler equipped with the brushless motor was tested with both constant speed and power control strategies. Results indicated the superiority of the proposed brushless motor drive and power control scheme.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Space Vector Based Capacitor Voltage Balancing for a Three-Level NPC
           Traction Inverter Drive
    • Authors: Abhijit Choudhury;Pragasen Pillay;
      Pages: 1276 - 1286
      Abstract: A dc-link capacitor voltage balancing topology based on virtual space vector is proposed for traction drive application in the field-weakening region. Four different strategies are implemented and their duty ratios are individually derived. The system is then connected to an interior permanent magnet synchronous machine (IPMSM) generally used for traction applications. A comprehensive investigation on the capacitor voltage variation in the field-weakening region is studied and the main contributing vectors are identified. All the required duty cycles of the vectors are analytically calculated based on the three nearest available voltage vectors. All the four proposed strategies helped to minimize the neutral point potential fluctuation (NPPF) considerably in comparison to the earlier proposed schemes. The proposed scheme is then supported by the simulation and experimental verification with a 6.0-kW IPMSM.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Phase Synchronization Technique Based on Perturbation and Observation
           for Bidirectional Wireless Power Transfer System
    • Authors: Fang Liu;Kai Li;Kainan Chen;Zhengming Zhao;
      Pages: 1287 - 1297
      Abstract: For the bidirectional wireless electric vehicle charging system, when both the primary and secondary converters are active, the phase synchronization between the two converters are necessary to control the power flow direction. This article proposes a new phase synchronization method by tracking the maximum (or minimum, depending on the power flow direction) value of the output current, without auxiliary hardware or the real-time communication between the primary and secondary sides. First, the relationship between the output current and the phase difference of the control signals is derived. It is found that the maximum output current is determined by the relative phase-shift angle (time interval between the middle points of the primary and secondary voltages) and the internal phase-shift angles of the two converters (time interval when the output voltage equals to the dc-link voltage). Second, a new scheme for generating the control signals is proposed to ensure that the relative phase-shift angle is not influenced by the internal phase-shift angles. Third, based on the perturbation and observation method, a procedure is proposed to track the extreme value of the output current and obtain the target relative phase-shift angle for the phase synchronization state. Moreover, the relationship between the internal phase-shift angle and the transfer power is derived to regulate the magnitude of the transfer power, with the dead-time effect taken into consideration. Finally, experimental results verify the validity of the proposed method with different air gaps and power levels. The method is easy to be implemented, helpful for the optimal operation of the static and quasi-static wireless charging system and suitable for the bidirectional power flow.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Modulation Method for Improving Reliability of Multilevel T-Type Inverter
           in PV Systems
    • Authors: Mokhtar Aly;Emad M. Ahmed;Masahito Shoyama;
      Pages: 1298 - 1309
      Abstract: Multilevel inverters (MLIs) have proven superior performance in several applications, especially in photovoltaic (PV) applications. However, power switches in MLIs possess high failure rates due to unequal power losses distributions that shorten lifetime of the whole PV inverter. Therefore, a new pulsewidth modulation (PWM) methodology for loss balance in grid connected PV single-phase five-level inverters is presented in this paper. The proposed loss balance PWM (LBPWM) method is based on swapping the utilization of power switches through half or quarter of the fundamental line period based on the redundancies between the switching states in MLIs. In addition, the proposed LBPWM method achieves natural balance among voltages over the dc-link capacitors. The effectiveness and feasibility of the proposed LBPWM method are verified using the simulation environment and experimental prototype. Different operating conditions and points of PV inverters are investigated in addition to reliability evaluation of the PV inverter are provided. Moreover, the superior performance criterion of the proposed LBPWM methods are verified through comprehensive comparisons with the most prominent previously developed PWM methods in the literature. The generalization and implementation steps of the proposed LBPWM method are also provided.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Comprehensive Review and Comparison of Single-Phase Grid-Tied Photovoltaic
           Microinverters
    • Authors: Khalil Alluhaybi;Issa Batarseh;Haibing Hu;
      Pages: 1310 - 1329
      Abstract: The power processing and the presence of the electrical isolation between the PV module and the grid is a very crucial aspect in determining the performance requirement, as well as the utility operator's specifications for the PV microinverter design. The grid-connected PV microinverter design can be classified into four categories: 1) nonisolated single-stage topologies; 2) isolated single-stage topologies; 3) nonisolated double-stage topologies; and 4) isolated double-stage topologies. Typically, a microinverter's performance can be enhanced by the use of nonisolated topologies to be more efficient, more compact, less bulky, and less costly than the isolated topologies. Whereas, the use of a transformer in microinverter topologies provides high-power quality as well as galvanic isolation to eliminate the safety issues, which in return meet the grid standards. The power processing (boosting the dc voltage of PV panel, extracting the maximum power and converting it to ac power), which can be achieved either via single stage or double stage, has a significant impact on the microinverter performance. This paper reviews and compares experimentally verified microinverter topologies in terms of their corresponding efficiency, power density, reliability, and cost. The most efficient topology in each category is designed and simulated in comparison with a benchmark. The topologies are then compared in terms of their component count, input voltage range, modular structure, soft-switching implementation, and battery integration.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Novel Four-Port DC–DC Converter for Interfacing Solar PV–Fuel Cell
           Hybrid Sources With Low-Voltage Bipolar DC Microgrids
    • Authors: Prajof Prabhakaran;Vivek Agarwal;
      Pages: 1330 - 1340
      Abstract: Bipolarity in dc microgrids is desirable as it enhances the system reliability and efficiency. However, a bipolar dc microgrid (BDCMG) demands multiple conventional dc-dc converters to feed power to both the poles of the BDCMG. To handle this requirement and to maintain high efficiency, a new four-port, dual-input-dual-output dc-dc converter topology is proposed for interfacing the solar photovoltaic (PV) and fuel cell sources to a low-voltage BDCMG. The proposed topology is unidirectional, efficient, and compact. It has fewer circuit elements with only one inductor compared to the conventional nonisolated dc-dc converters. The proposed converter regulates one of the pole voltages of the dc bus and also ensures maximum power point tracking of the PV source. Furthermore, the converter can be operated as a single-input-dual-output converter. The control complexity of the proposed converter is low as it can be operated in various modes with only one set of controllers. To design the control system for the proposed converter, a small-signal model is derived for each operating mode. Loss modeling and efficiency analysis of the proposed converter are carried out, and its efficacy and performance are validated by detailed simulation and experimental results under various operating conditions.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Harmonic Compensation Strategy for Extending the Operating Range of
           Cascaded H-Bridge PV Inverter
    • Authors: Tao Zhao;Xing Zhang;Wang Mao;Mingda Wang;Fusheng Wang;Xinyu Wang;Jun Xu;
      Pages: 1341 - 1350
      Abstract: For single-phase cascaded H-bridge (CHB) photovoltaic (PV) inverters, all the PV modules are able to operate at the maximum power point, which is beneficial to energy harvesting. However, due to the stochastically variable irradiance level and ambient temperature, the unbalanced output powers among PV modules may cause the overmodulation of the H-bridges with higher power, ultimately resulting in a distorted grid current. In this paper, a novel harmonic compensation strategy is proposed. Compared to the existing methods, it can not only ensure that CHB inverter operates at unity power factor with small dc-bus voltage ripple but also keep the total harmonic distortion of grid current in acceptable range under some heavy power unbalance conditions, so it has a good overall performance. Simulation and experimental results validate the effectiveness and feasibility of the proposed method.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Unified Control Scheme for a Standalone Solar-PV Low Voltage DC
           Microgrid System With HESS
    • Authors: Sijo Augustine;Mahesh K. Mishra;N. Lakshminarasamma;
      Pages: 1351 - 1360
      Abstract: This paper proposes a combined adaptive droop-based load sharing, maximum power point tracking (MPPT), and energy management of photovoltaic (PV)-based dc microgrid system. A proportional droop index (PDI) algorithm is introduced, which is a function of normalized current sharing difference and voltage deviation at the output side of the converter. The proposed method calculates adaptive virtual resistance Rdroop, which allows the PV converter to operate at MPP or load sharing mode. By fine-tuning Rdroop values, the proposed method eliminates poor voltage regulation issues of the conventional droop method. The control of the hybrid energy storage system (HESS) with a battery and a supercapacitor (SC) is also discussed to stabilize the dc grid voltage and energy management of the dc microgrid. The detailed analysis and the design procedure of low-voltage (LV) dc microgrid systems are explained, and the effectiveness of the proposed method is verified by simulation and experimental studies.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Detection and Identification of Global Maximum Power Point Operation in
           Solar PV Applications Using a Hybrid ELPSO-P&O Tracking Technique
    • Authors: J. Prasanth Ram;Dhanup S. Pillai;N. Rajasekar;Scott M. Strachan;
      Pages: 1361 - 1374
      Abstract: Nonhomogeneous irradiation conditions due to environmental changes introduce multiple peaks in nonlinear P -V characteristics. Hence, to operate photovoltaic at the global power point, numerous algorithms have been proposed in the literature. However, due to the insufficient exploitation of control variables, all the maximum power point tracking (MPPT) methods presented in the literature fail to guarantee global maximum power point (GMPP) operation. In this paper, a new detection technology to identify GMPP zones using hybrid enhanced leader particle swarm optimization (ELPSO) assisted by a conventional perturb and observe (P&O) algorithm is proposed. With inherent mutations, ELPSO applied to MPPT excels in exploring global regions at initial stages to determine the global best leader, whereas P&O is reverted back soon after global solution space is detected. The transition from ELPSO to P&O is mathematically verified and allowed only when ELPSO finds the global optimal zone. Adapting this hybrid strategy, the proposed method has produced interesting results under partial shaded conditions. For further validation, the results of the proposed hybrid ELPSO-P&O are compared with the conventional ELPSO and the hybrid PSO-P&O methods. The experimental results along with energy evaluations confirmed the superiority of the ELPSO-P&O method in obtaining the maximum available power under all shaded conditions.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Impedance Modeling and Stability Analysis of Grid-Connected DFIG-Based
           Wind Farm With a VSC-HVDC
    • Authors: Kun Sun;Wei Yao;Jiakun Fang;Xiaomeng Ai;Jinyu Wen;Shijie Cheng;
      Pages: 1375 - 1390
      Abstract: A new type of subsynchronous oscillation (SSO) has been observed recently in double-fed induction generator (DFIG)-based wind farm integrated via voltage source converter-based HVdc (VSC-HVdc) system. However, the mechanism of this emerging oscillation is not entirely understood. In this paper, the impedance models of DFIG with and without considering the phase-locked loop (PLL) dynamics are both derived. Then, the impedance-based simplified equivalent circuit of the multiple DFIGs interfaced with VSC-HVdc system is established. This model can be further represented as the RLC series resonance circuit to quantify the start-oscillating condition intuitively. The theoretical analysis results show that DFIGs behave as an inductance in series with a negative resistance at the resonance point, whose interaction with wind farm side VSC (WFVSC) (regard as a resistance-capacitance) constitutes an equivalent RLC resonance circuit with negative resistance. Therefore, the oscillation tends to occur due to the negative damping. In addition, the impact of various factors including number of grid-connected DFIG-wind turbines (WTs), wind speed, and parameters of PI controllers and PLL on the SSO characteristics is analyzed based on the proposed simplified model. Finally, the correctness of the theoretical analysis is validated by both the time-domain simulation and hardware-in-loop experiments.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Novel Predictive Fuzzy Logic-Based Energy Management System for
           Grid-Connected and Off-Grid Operation of Residential Smart Microgrids
    • Authors: Mohammad Jafari;Zahra Malekjamshidi;Jianguo Zhu;Mohammad-Hassan Khooban;
      Pages: 1391 - 1404
      Abstract: In this paper, a novel energy management system (EMS) with two operating horizons is proposed for a residential microgrid application. The microgrid utilizes the energies of a photovoltaic, a fuel cell (FC), and a battery bank to supply the local loads through a combination of electric and magnetic buses. The proposed microgrid operates in a large number of grid-connected and off-grid operation modes. The EMS includes a long-term data prediction unit based on a 2-D dynamic programing and a short-term fuzzy controller. The long-term prediction unit is designed to determine the appropriate variation range of the battery state of charge and FC state of hydrogen. The efficiency performance of the microgrid components, predicted energy generation and demand, energy cost, and the system constraints are taken into account. The resultant data then are sent to the short-term fuzzy controller which determines the operation mode of the microgrid based on the real-time condition of the microgrid elements. A prototype of the proposed microgrid including the EMS is developed, and experimental tests are conducted for three different energy management scenarios. The proposed management technique is validated through energy distribution and cost analysis.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Multiport Railway Power Conditioner and Its Management Control Strategy
           With Renewable Energy Access
    • Authors: Fujun Ma;Xin Wang;Lingfeng Deng;Zhen Zhu;Qianming Xu;Ning Xie;
      Pages: 1405 - 1418
      Abstract: To achieve the mutual benefits between railway systems and renewable energy systems, a multiport railway power conditioner (MP-RPC) with the renewable energy access is proposed to realize the on-site power consumption and negative-sequence compensation. Its power-flow management strategy with five classic operation modes is proposed and analyzed for MP-RPC. The key part of MP-RPC is three-port isolated dc/dc converters, which can be used for the isolation and power transmission. Through the small-signal modeling and analysis of the three-port converter, the port power control strategy with feed-forward decoupling is applied. The coupling system is decoupled into two independent control loops based on the feed-forward decoupling matrix, which can effectively improve the dynamic performance of system. Finally, the traction power platform and simulated prototype are built in the Laboratory, and the topology and control methods of MP-RPC are verified effectively.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A High-Efficiency and Long-Distance Power-Relay System With Equal Power
           Distribution
    • Authors: Fei Lu;Hua Zhang;Weiguo Li;Zhe Zhou;Chong Zhu;Chenwen Cheng;Zhanfeng Deng;Xi Chen;Chunting Chris Mi;
      Pages: 1419 - 1427
      Abstract: This paper proposes a wireless power repeater system for long-distance and multiple-load applications with equal power load at each repeater. Each repeater performs as a power relay that not only receives and transmits power but also supplies power to its local load. The main contribution of this paper is to provide the design methodology of a distributed power-relay system. First, it provides the mathematical model of the power distribution among the power relays, indicating that the inductances and resistances can affect the power distribution. Second, it provides the power transfer capability of a power-relay system based on the quality factor and efficiency requirement, indicating the maximum achievable number of power relays in a system. Aiming at practical applications, this paper provides the guideline for the circuit parameter design to achieve equal power distribution. Two typical examples are proposed to realize equal power distribution. The identical Mn and different Rn examples are selected for implementation. The coil size is 400 mm × 400 mm, and the eight power relays achieve a transfer distance of 3.2 m with a total power of 760 W and an efficiency of 70%. Experimental results validate that equal power distribution is achieved for the multiple loads across a long distance. Each power relay dissipates about 95-W power in its local load with a power variation limited to ±2%.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Self-Adaptation Control of Second-Life Battery Energy Storage System Based
           on Cascaded H-Bridge Converter
    • Authors: Chang Liu;Xu Cai;Qiang Chen;
      Pages: 1428 - 1441
      Abstract: The biggest challenge for the adoption of battery energy storage system (BESS) is its affordability at an acceptable performance. The battery is the single largest cost item for BESS currently. A second-life use of the transportation battery after degradation in BESS can make the overall cost more acceptable, which is significant for the speedier and wider application of BESS in power systems. A cascaded H-bridge converter integrated with split second-life battery modules has been proposed in this paper. The relatively big parameter differences in evolving battery modules compared with the new one, such as effective capacity, impedance, initial state, and the uncertainty of degradation will lead to overcharge and overdischarge of the second-life battery modules. The underutilization of effective battery capacity will also arise simultaneously. In order to suitably integrate and control these widely different battery modules, a self-adaptation control strategy of the system based on online capacity estimation is proposed. Then, these second-life battery modules tend to react in significantly different ways according to their characteristics. Moreover, the proposed strategy can make corresponding adjustments according to parameter changes of the battery modules and is more adaptive to the dynamic operation condition. Finally, Modeling, analysis, and experimental validation are performed on a downscaled prototype in laboratory.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Autonomous Power-Source Regulation in Series-Connected Low-Voltage
           Microinverters
    • Authors: Fenglong Lu;Beomseok Choi;Dragan Maksimovic;
      Pages: 1442 - 1453
      Abstract: This paper is focused on a photovoltaic system architecture based on series-connected low-voltage ac (LVac) microinverters. In contrast to standard microinverters, LVac microinverters do not require high step-up conversion stages, which leads to potentials for improved efficiency and reduced cost. This paper proposes a distributed autonomous control strategy for the LVac microinverters, where each module is operated autonomously by a controller that regulates instantaneous output power. Modeling of system dynamics is challenging due to the nonlinear and time-varying nature of the system. Under quasi-static assumptions, a linearized small-signal model is obtained and solved along the operating points traversed during a line cycle. The modeling approach and controller design are verified by simulations and experiments on a scaled-down system consisting of three series-connected LVac microinverters, demonstrating appropriate ac voltage sharing across the modules. In certain cases, including a low compensator gain in the control loop, significant total harmonic distortion (THD) is observed in the ac line current. In order to reduce the distortion, a pre-distortion technique is used in each LVac control loop to compensate the sinusoidal input reference. The experimental results demonstrate that the predistortion technique reduces the THD to 3%-4% across a wide operating range, without the need for additional electro-magnetic interference filter stages.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Generalized Controller for Electric-Spring-Based Smart Load With Both
           Active and Reactive Power Compensation
    • Authors: Tong Chen;Heng Liu;Chi-Kwan Lee;S. Y. Ron Hui;
      Pages: 1454 - 1465
      Abstract: With the electric spring (ES) being practically evaluated by utility companies in power grids, there is a need to explore its practical implementation aspects of general applications. In this paper, we propose three interior angle control principles for the ES. Systematic analysis and comparative study show that these three control principles lead to different smart load (SL) performance. The operating characteristic curves and distinctive features/advantages of the SL using these three control methods are analyzed and explained. A generalized controller structure suitable for the implementations of all these three angle control schemes is presented. It is practically shown that the same controller structure can be programmed to implement these three angle control strategies. This outcome is the first step to realize a programmable ES-based SL for providing multiple functions.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Improving the Reactive Current Compensation Capability of Cascaded
           H-Bridge Based STATCOM Under Unbalanced Grid Voltage
    • Authors: Yousef Neyshabouri;Sanjay K. Chaudhary;Remus Teodorescu;Rahman Sajadi;Hossein Iman-Eini;
      Pages: 1466 - 1476
      Abstract: This paper deals with the operation of a cascaded H-bridge (CHB) converter-based STATCOM under unbalanced grid conditions. Degrees of freedom and operational limitations of the CHB STATCOM during unbalanced grid condition are analyzed according to the converter power flow equations. Based on this analysis, an improved low-voltage ride-through (LVRT) strategy for the CHB STATCOM is proposed. In this strategy, the grid operator can control both the positive- and negative-sequence reactive currents independently within the operation range of the CHB STATCOM. In addition, to keep the submodules' capacitors voltages balanced, a zero-sequence voltage term is injected to the converter legs. The negative-sequence active current is also controlled to limit the injected zero-sequence voltage and keep the converter within the rated operation range. The performance and effectiveness of the proposed method are validated through PSCAD/EMTDC simulation of a 21-level CHB STATCOM. The results are experimentally demonstrated on a 9-level CHB STATCOM prototype.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Virtual Impedance Design Considerations for Virtual Synchronous Machines
           in Weak Grids
    • Authors: Alberto Rodríguez-Cabero;Javier Roldán-Pérez;Milan Prodanovic;
      Pages: 1477 - 1489
      Abstract: Most renewable energy sources (RESs) are interfaced to electricity grids via voltage-source converters (VSCs). To facilitate the integration, the controllers based on the emulation of synchronous generators have been increasingly used. This control technique is commonly referred to as Virtual Synchronous Machine (VSM) and recent studies have shown that VSMs are sensitive to variations in the network parameters if no countermeasures in form of virtual impedances are applied. However, a thorough and comprehensive methodology for the design of virtual impedance for VSMs has not been yet presented in the literature and the development of such procedure for the VSMs connected to weak grids is the principal objective of this paper. Each dynamic element of the VSM is modeled and all of them are then joined together forming a state-space model. The eigenvalue and singular value decomposition (SVD) analyzes were used then to evaluate the impact of the grid model and the virtual impedance on the VSM dynamics. From these results, a practical guide to design both the VSM and the virtual impedance parameters was proposed. All the theoretical developments were validated experimentally on a 15-kVA prototype of a VSM connected to a weak grid.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Comprehensive Study to Mitigate Voltage Sags and Phase Jumps Using a
           Dynamic Voltage Restorer
    • Authors: Chunming Tu;Qi Guo;Fei Jiang;Hongliang Wang;Zhikang Shuai;
      Pages: 1490 - 1502
      Abstract: This paper introduces an efficient strategy to improve the voltage quality of sensitive loads with the optimal utilization of a dynamic voltage restorer (DVR). Traditional control strategies mainly focus on the voltage compensation stage to reduce the voltage rating of the DVR or minimize the required capacity of the energy storage device. In addition, the phase jump correction in the early stage of the compensation has attracted more attention as well. In reality, phase jump issues may occur in the initial and final stages of compensation, and they must be avoided for most loads, but few works focus on how a DVR can smoothly exit the system after the fault elimination. With the main objective of mitigating the phase jump in the load side voltage while improving the overall sag compensation time, this paper demonstrates that: 1) based on energy-optimized compensation strategies, the proposed approach aims at completing the smooth transition of the transient process during the voltage compensation and recovery stages and ensuring effective linkage from the former to the latter and 2) the mode operation boundaries in the two stages are derived and compared, and the updated procedure of a new injected reference voltage is activated to prevent the system from going outside its operating limits. Furthermore, the operation logic and the overall control scheme are elaborated, which ensure that the proposed approach preserves superior controllability to provide flexible voltage support. Finally, a combination of simulation and experimental results is used to validate the performance of the proposed method.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Coordinative Low-Voltage-Ride-Through Control for the Wind-Photovoltaic
           Hybrid Generation System
    • Authors: Yufei He;Minghao Wang;Zhao Xu;
      Pages: 1503 - 1514
      Abstract: The wind-photovoltaic (PV) hybrid renewable energy system (HRES), which consists of permanent-magnet synchronous generators (PMSG) and PV arrays, is becoming a cost-effective electric source for powering islanded areas. However, high penetration of renewables makes the power system vulnerable to transient voltage faults, which undermines the stability of the future inverter-dominated grid. To address this issue, a coordinative low-voltage-ride-through (LVRT) control scheme is proposed for the operation of the wind-PV HRES in this article. This control scheme will exploit the maximum energy inertia of the HRES for incorporating the power imbalance between the faulted grid and the renewable generators. An optimization problem is formulated to maximize the renewable energy harvesting within the operational and environmental limitations. To cope with different working conditions, four control processes are coordinated in an optimized manner during the LVRT period: 1) adaptive dc-link voltage control; 2) PMSG rotating speed control; 3) PV energy curtailment control; and 4) blade pitch angle control. Besides, this control scheme applies a direct output control that can generate stable and accurate current as per grid code requirements. The results of the hardware-in-the-loop (HIL) experiment and the MATLAB/Simulink simulation are provided to verify the effectiveness of the proposed control scheme.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Mechanism Analysis of DFIG-Based Wind Turbine’s Fault Current During
           LVRT With Equivalent Inductances
    • Authors: Yuanzhu Chang;Jiabing Hu;Xiaoming Yuan;
      Pages: 1515 - 1527
      Abstract: Doubly fed induction generator (DFIG)-based wind turbine (WT) has a distinct fault current contribution that is critical for the power system analysis. This article analyzes the mechanism underlying DFIG-based WT's fault current during the low-voltage ride through (LVRT) from the perspective of magnetic circuits. The crowding-out phenomenon is discovered, and the general relationship between flux linkage and current is depicted with the proposed equivalent inductances. Based on the understanding, a new analytical method for deriving the analytical expressions of fault current is proposed. Compared with the existing methods that rely on solving the ordinary differential equations (ODEs), the proposed method is based on the algebraic operation derived from the magnetic circuits, which makes it appropriate for different fault scenarios. Using this method, the stator current is depicted with a series of succinct expressions. The analytical results are verified by experiments and simulations on a 10-kW DFIG prototype. The differences in fault current between the synchronous generator (SG) and DFIG-based WT are identified. This article is expected to help in understanding the regularities of DFIG-based WT's fault current from a physical perspective. The analytical results are expected to be helpful for rating circuit breakers and studying issues related to protective relays.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Novel Feedforward Stabilizing Technique to Damp Power Oscillations
           Caused by DC–DC Converters Fed From a DC Bus
    • Authors: Mosaddique Nawaz Hussain;Vivek Agarwal;
      Pages: 1528 - 1535
      Abstract: Switched-mode power electronic converters with feedback control tend to behave like Constant Power Loads (CPLs). When a CPL interacts with a poorly damped input LC filter, it amplifies any disturbance that occurs in the LC circuit, and the system becomes prone to instability. If the CPL is emulated as a positive resistance during any disturbance by manipulating the power that it consumes instantaneously, then the instability can be avoided. In this paper, this has been achieved by a feedforward technique, in which the power consumed by the CPL is made to follow the trajectory of the input voltage during any disturbance similar to the power consumed by a resistive load. The proposed feedforward technique has only one variable that can be determined by the input filter parameters and is independent of the type of the CPL. A case of a dc-dc converter-based CPL is studied in this paper, and the proposed technique is shown to create a virtual RC impedance at the input of the CPL to offset the negative resistance behavior. The effectiveness of the proposed technique is showcased through the detailed simulations and experimental studies on a 100-W CPL prototype.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Bidirectional Current Injection MVDC Circuit Breaker: Principle and
           Analysis
    • Authors: Yifei Wu;Yi Wu;Fei Yang;Mingzhe Rong;Yang Hu;
      Pages: 1536 - 1546
      Abstract: The medium-voltage dc (MVDC) interruption technology has grown in recent years, driven by increased interest in using MVDC system for integrating distributed renewable energy and improving the efficiency of power supply. In this paper, two topologies of current injection MVDC breaker are focused on. The first topology is based on conventional precharged capacitor that utilizes a bridge-type commutation branch to realize the freewheeling for the interrupter and bidirectional breaking. With the help of simulation, the effect of stray inductances on the current commutation capability is analyzed in detail, and then, a prototype of the MVDC breaker is built to test the fault current breaking performance. The second topology is an improved MVDC breaker based on magnetic induction current commutation module (MICCM). With MICCM analyzed carefully in terms of circuit and structure parameters for determining their optimal values, the prototype of the improved 10-kV dc breaker is built and tested, which validates the feasibility and effectiveness of improved topology.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Comparative Study of Switched-Tank Converter and Cascaded Voltage
           Divider for 48-V Data Center Application
    • Authors: Xiaofeng Lyu;Yanchao Li;Na Ren;Shuai Jiang;Dong Cao;
      Pages: 1547 - 1559
      Abstract: This paper presents a comparative study of the switched-tank converter (STC) and the cascaded voltage divider (CVD). The operating principles of the STC and the CVD with four times input-to-output conversion ratio ($4times$ ) are discussed. Two design approaches of the CVD are considered, including the high-density CVD (CVD-HD) and the high-efficiency low-density CVD (CVD-LD). The power loss breakdown analysis and system efficiency evaluation are provided for both converters. From these results, it is found that the STC is more efficient and smaller in size than the CVD converter. Gallium nitride (GaN)-based hardware prototypes of both converters are built and tested. The $4times $ -STC can achieve ~1500-W/in3 power density and 98.79% efficiency. The $4times $ -CVD-LD can achieve 1061-W/in3 power density and 98.41% efficiency. Therefore, the $4times $ -STC has 41% higher power density and 24% less power loss than the $4times $ -CVD-LD.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Family of Interleaved High Step-Up Converters With
           Diode–Capacitor Technique
    • Authors: Yifei Zheng;Wenhao Xie;Keyue Ma Smedley;
      Pages: 1560 - 1570
      Abstract: This paper presents a family of multiphase interleaved high step-up dc-dc converters using the diode-capacitor technique, which is an extension of the previously reported current-fed Cockcroft-Walton (CW) multiplier. The multiphase configuration has the advantages of low input current ripple, high current-handling capability, and high step-up voltage gain. Also, the switches and diodes have low voltage stresses. Thus, low-voltage-rating semiconductor devices are allowed reducing the conduction loss. Moreover, automatic phase current balancing can be achieved due to the charge balance of the series capacitors. A three-phase high step-up converter in the family is analyzed and evaluated in detail. The simulation and experimental results are provided to verify the theoretical analysis.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Decentralized Suppression Strategy of Circulating Currents Among IPOP
           Single-Phase DC/AC Converters
    • Authors: Yanghong Xia;Miao Yu;Yong Zhang;Zeyan Lv;Wei Wei;
      Pages: 1571 - 1583
      Abstract: To increase the power rating and improve the reliability of the single-phase power supply system, the input-parallel output-parallel (IPOP) single-phase dc/ac converters (SDACs) are widely used. However, among the IPOP SDACs, there are complicated circulating currents which will increase the current stress on the switching devices and influence the safe operation of the system. But, the detailed quantitative analysis of the circulating currents is not well developed and the corresponding suppression strategies are not very comprehensive. Focusing on these problems, this paper pays attention to the detailed mathematic model and effective suppression strategy of circulating currents among IPOP SDACs. First, the detailed mathematic model of the circulating currents is established. Based on this model, it is found that there are various types of circulating currents existing in the IPOP SDACs, including circulating currents within the single SDAC and circulating currents among the multiple SDACs. At the same time, the influence factors are also analyzed, and it is first revealed that the asymmetry of impedances in different sides will cause circulating currents with different frequencies components including the dc, fundamental, and second frequencies. Second, after the detailed analysis, a decentralized control method composed of the common mode (CM) and differential mode (DM) control is proposed to suppress the complicated circulating currents. The control method is comprehensive and can suppress circulating currents caused by diverse influence factors. All the theoretical analyses are verified by the real-time hardware-in-loop (HIL) tests.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • An Ultrahigh Step-Up Nonisolated Interleaved Converter With Low Input
           Current Ripple
    • Authors: Mahdi Shaneh;Ehsan Adib;Mehdi Niroomand;
      Pages: 1584 - 1592
      Abstract: In this paper, a new topology to achieve ultrahigh step-up voltage conversion ratio and very low input current ripple is introduced for nonisolated high-power applications by using interleaved structure combined with coupled inductors (CIs) and switched capacitors. Using voltage lift capacitors in this topology not only recycles the energy related to leakage inductance of CIs and alleviates the voltage spike across the power switches but also increases the voltage gain of the converter. Moreover, utilizing CI structure provides zero-current switching (ZCS) turn-on condition for power switches and reducing the diodes reverses recovery losses and also improves the voltage gain of the converter. Using the interleaved structure in the low-voltage side noticeably decreases the input current ripple and current stress through magnetic elements. In addition, utilizing the voltage multiplier cell structure in the high-voltage side provides a high-voltage gain. The voltage stress across the power switches is considerably lower than the output voltage. Hence, the low-voltage-rated switches can be employed. Based on the mentioned advantages, the efficiency of this implementation is improved significantly. Finally, to validate the performance of the proposed converter, a 600-W, 24-V/520-V prototype circuit is implemented.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Adaptive Reference Trajectory for Power Quality Enhancement in Three-Phase
           Four-Wire Standalone Power Supply Systems With Nonlinear and Unbalanced
           Loads
    • Authors: Abdelhakim Saim;Azeddine Houari;Mourad Aït Ahmed;Ali Djerioui;Mohamed Machmoum;Josep M. Guerrero;
      Pages: 1593 - 1603
      Abstract: This article presents an advanced control strategy for power quality enhancement in standalone power supply systems (PSSs) with grid forming four-leg voltage source inverters (FL-VSIs). Indeed, an online adaptive reference generator (ARG) with a gray wolf optimizer (GWO) is proposed to sustain the control performances of a feedback linearization control (FLC) strategy and improve its robustness against load-side disturbances and system parameters' uncertainties. The key purpose of the proposed GWO-based ARG is to compensate for load and phase disturbances through smooth reference adjustments, in order to improve the voltage waveforms' quality and symmetry and conform to the existing power quality standards and metrics. The design methodology of the proposed control approach is thoroughly detailed, and its effectiveness is asserted through simulation and experimental tests, demonstrating its superiority in maintaining the voltage waveforms within the required standard limitations even under unbalanced and nonlinear loading conditions.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • PCB-Level Stress Analysis of an Integrated Module Based on Reversely
           Switched Dynistor
    • Authors: Lin Liang;Lianghao Liu;Shilei Wang;Cai Chen;
      Pages: 1604 - 1610
      Abstract: In this paper, the effects of thermal stress and electromagnetic force on PCBs at different frequencies and different pulse current levels in reversely switched dynistor-based pulse power integration modules are studied. According to the theory of the electromagnetic field and thermodynamics, the electromagnetic field and temperature field of the pulse power integrated module are simulated and analyzed by finite-element method. The electromagnetic force and thermal stress on the PCB pad are obtained and their impacts on the pads are compared at different conditions. The simulation results show that the maximum electromagnetic force and thermal stress appear on the pad connected to the capacitor pin. The electromagnetic stress increases with the increase in the amplitude of the current. The thermal stress increases with the increase in the amplitude and the frequency of the current. According to the general specification of the rigid printed circuit board GJB 362B-2009, taken the pull-out force of pads as a standard, the limiting current is determined by the electromagnetic stress at low frequency and by the thermal stress at high frequency.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Assist Gate Driver Circuit on Crosstalk Suppression for SiC MOSFET Bridge
           Configuration
    • Authors: Hui Li;Yi Zhong;Renze Yu;Ran Yao;Haiyang Long;Xiao Wang;Zhangjian Huang;
      Pages: 1611 - 1621
      Abstract: Crosstalk in a phase-leg configuration significantly limits the high switching speed performance of silicon carbide (SiC) MOSFET due to their lower threshold voltage and higher allowable negative gate voltage as compared with the traditional silicon (Si). To fulfill the potential fast switching speed quality of SiC MOSFET, an assist gate driver (AGD) circuit for crosstalk suppression based on the negative-biased turn-off voltage was proposed, which contains an auxiliary capacitor and two passive transistors without additional control signals. First, a recommended gate driver by several SiC device manufacturers was introduced to analyze the mechanism of crosstalk. Then, the operating principle of the proposed AGD circuit was elaborated, and the parameter design criteria of the main elements were given. Finally, a simulation using LTspice and an experiment based on Wolfspeed 1200-V SiC MOSFET tests were used to verify the effectiveness of the proposed gate driver. Simulation and experimental results show that the AGD circuit has a superior characteristic of crosstalk suppression under varying operating conditions. Thus, the proposed circuit could meet the fastidious requirement of fast-speed SiC MOSFET under high dc voltage condition with less complexity.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Study of Current Density Influence on Bond Wire Degradation Rate in SiC
           MOSFET Modules
    • Authors: Haoze Luo;Francesco Iannuzzo;Nick Baker;Frede Blaabjerg;Wuhua Li;Xiangning He;
      Pages: 1622 - 1632
      Abstract: This paper proposes a separated test method for studying the current effect on the ageing process of a wire-bonded silicon carbide (SiC) MOSFET module under power cycling test (PCT). The separated test method enables testing SiC MOSFET at different load current densities, but under the same temperature swing and average temperature conditions. By analyzing the output characteristics in the linear region, the relationships among the gate voltage, on-state voltage, and junction temperature are revealed. Then, the one-to-one correspondence between gate voltage and conduction power loss can be used to adjust the current density under the same temperature conditions. Two six-pack SiC modules (1200 V/20 A) are tested under 12 and 24 A conditions to experimentally verify the proposed method. The ageing curves show that the high current can speed up the ageing rate of bond wires even under the same temperature conditions (65 °C-125 °C). Moreover, the high current density also has an impact on solder layer degradation as well as on the temperature conditions. Finally, a power device analyzer B1506A and a scanning acoustic microscope (SAM) are used to investigate the degradation of electrical parameters and the solder layer, respectively. The final summary of analytical results shows that the input current has a nonnegligible impact on the degradation process of power modules.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • High-Current Switched Capacitor Converter for On-Package VR With PDN
           Impedance Modeling
    • Authors: Mario Ursino;Stefano Saggini;Shuai Jiang;Chenhao Nan;Roberto Rinaldo;Roberto Rizzolatti;
      Pages: 1633 - 1643
      Abstract: Digital ASIC devices are widely used in networking and computing applications. This kind of devices is implemented with a short-channel technology requiring high peak currents for high complexity systems and a low supply voltage. Digital ASICs are powered by an external voltage regulator with specifications similar to modern microprocessors' power supply [voltage regulation modules (VRMs)]. In order to reduce the number of power pins and to reduce the power distribution network (PDN) issue, Intel's Fourth-Generation Core integrates the voltage regulators. Moreover, many on-package conversion systems are present in the literature. In this article, a conversion solution based on a switched resonant tank is presented, yielding currents up to 300 A at 0.8 V, in an area of 10 cm2, with a resonant-driving technique. The novel converter is used to validate a new linear time-periodic (LTP) system modeling approach that can be applied to generic switched topologies; this contribution yields a mathematical description of the conversion chain, in particular enabling the precise calculation of the output impedance when a switched topology is used as the last stage.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • An Accurate Calorimetric Loss Measurement Method for SiC MOSFETs
    • Authors: Anup Anurag;Sayan Acharya;Subhashish Bhattacharya;
      Pages: 1644 - 1656
      Abstract: An accurate measurement of conduction and switching losses in the power semiconductor devices is necessary in order to design and evaluate the thermal management system of modern converter systems. Conventionally, electrical measurement methods, such as the double-pulse tests (DPTs), are used for measuring the switching losses. However, with the advent of wide-bandgap (WBG) devices that have fast switching transients, it is rather difficult to capture the waveforms accurately during switching transitions, and consequently, the measurement of switching loss becomes inaccurate. In addition, the measurement of switching waveforms depends on the voltage and current probes, as well as the oscilloscope used for the measurement, which makes this method prone to errors. This necessitates the use of measurement methods, which can provide much higher accuracy than the existing conventional electrical methods. Calorimetric methods are based on comparatively slow temperature measurements and do not rely on the measurements of fast switching transitions of voltages and currents, thus eliminating the demand for measuring fast switching transitions. This paper presents an accurate calorimetric method for measuring the device losses, which can be used to determine individual loss components accurately (conduction, turn-on, and turn-off losses). In addition to the turn-on and turn-off losses, this method can evaluate the charging and discharging losses of the device. The novelty of the method lies in the fact that a single setup can be used to measure all possible losses that can occur in a device during converter operation. The calorimetric test setup is described, and a novel modulation scheme is introduced, which enables the segregation of the individual losses. The experimental test setup is built and the method is verified by measuring the losses of a 900-V, 23-A Wolfspeed C3M0120090D SiC MOSFET.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Role of Threshold Voltage Shift in Highly Accelerated Power Cycling Tests
           for SiC MOSFET Modules
    • Authors: Haoze Luo;Francesco Iannuzzo;Marcello Turnaturi;
      Pages: 1657 - 1667
      Abstract: In silicon carbide (SiC) power MOSFETs, threshold voltage instability under high-temperature conditions has potential reliability threats to long-term operation. In this paper, the threshold voltage shifts caused by the instability mechanisms in accelerated power cycling tests for SiC MOSFETs are investigated. In conventional power cycling tests, the positive threshold voltage shift can cause successive ON-state resistance increases, which can sequentially increase junction temperature variations gradually under fixed test conditions. In order to distinguish the increased die voltage drop from the bond wire resistance degradation, an independent measurement method is used during the power cycling tests. As the number of cycle increases, SiC die degradation can be observed independently of bond wire increases during the tests. It is studied that the SiC die degradation is associated with the threshold voltage instability mechanisms. Unlike the bond wire lift-off failure, the die degradation and the related die resistance increase can stop the power cycling test earlier than expected. In addition, a new test protocol considering the die degradation is proposed for the power cycling test. By means of power device analyzer, the failure mechanism and the degradation performance of SiC MOSFETs before and after the power cycling test are compared and discussed. Finally, experimental results confirm the role of threshold voltage shifting and identify different failure mechanisms.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Control Approach to Enhance the Performance of a Current-Fed Switched
           Inverter
    • Authors: Anil Gambhir;Santanu K. Mishra;Avinash Joshi;
      Pages: 1668 - 1685
      Abstract: Current-fed switched inverter (CFSI), a derivative of Z-source inverter, has the advantages of lower component count, single-stage conversion, high gain, and inherent shootthrough protection. But due to the limitation of modulation index, CFSI is forced to operate at higher dc-link voltage. As a result, voltage stress across the switches and capacitors increases. To mitigate this problem, a new pulsewidth modulation (PWM) technique is proposed. With the proposed scheme, CFSI can be operated at a lower dc-link voltage by increasing the modulation index. But operating at lower dc-link voltage increases peakto-peak ripple in the inductor current and leads to condition of early discontinuous conduction mode. Therefore, this paper also implemented a variable duty cycle (VDC) scheme, which reduces the peak-to-peak ripple in the input inductor current and increases the continuous conduction mode (CCM) operating range of CFSI. The proposed PWM scheme along with VDC scheme is validated for CFSI, which helps to: 1) reduce the voltage stress form 280 to 180 V; 2) reduce the input current ripple from 53.33% to 15.15%; 3) enlarge CCM range from 56% to 82%; and 4) improve the efficiency by 3.5%.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A PWM Strategy Based on State Transition for Cascaded H-Bridge Inverter
           Under Unbalanced DC Sources
    • Authors: Zongbin Ye;Tingting Wang;Shiqi Mao;Anni Chen;Dongsheng Yu;Xianming Deng;Tyrone Fernando;Maocai Chen;Shan Li;
      Pages: 1686 - 1700
      Abstract: A cascaded H-bridge (CHB) converter has been widely used and researched in industry since it is suitable for the operation under both normal and fault conditions. This paper proposes a novel pulsewidth modulation strategy based on state transition for CHB inverter with unbalanced dc sources to achieve high-quality line-to-line output voltages and maximize the linear modulation range. In this modulation strategy, the duration time of each switching state will be modified directly through the correction value. Ranges of correction value are derived by analyzing the modulation index limitation. Then, a proper correction value is added into duration times to transform the switching states and extend modulation index to the maximum value. Meanwhile, balanced ac currents can be obtained under unbalanced dc sources condition, even under larger unbalanced coefficients. Furthermore, a three-phase power control algorithm is introduced to achieve the balanced distribution of three-phase power. Compared with the traditional zero-sequence voltage injection method, the proposed strategy is more convenient and effective theoretically, and it can be applied to the higher level CHB converter. The advantage and effectiveness of the proposed strategy are verified by simulation and experimental results.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Family of Single-Stage High-Gain Dual-Buck Split-Source Inverters
    • Authors: Fazal Akbar;Honnyong Cha;Hafiz Furqan Ahmed;Ashraf Ali Khan;
      Pages: 1701 - 1713
      Abstract: In this paper, a family of single-phase single-stage high-gain dual-buck split-source inverters (SSIs) is proposed. The proposed inverters have the combine benefits of SSI, dual-buck inverter (DBI), and high-gain dc-dc converters. Similar to the DBI, they provide high reliability by eliminating shoot-through issues, increase switching frequency and efficiency by using power MOSFETs without leading the body diodes to reverse recovery issues, and decrease pulsewidth modulation (PWM) dead-time. In addition, voltage boost operation is achieved in a single stage without using any additional active switch, which is in favor of lower control complexity and lower cost. On the other hand similar to the SSI, buck-boost dc-ac power conversion is realized in a single stage. However, compared to the SSI, the proposed inverters have no shoot-through issues, MOSFETs can be used without reverse recovery issues, dead-time can be minimized, switching frequencies can be increased, and external fast recovery diodes can be used to improve efficiency. In addition, four different high-gain dual-buck SSIs are presented. As an example, the proposed switched-coupled-inductor split-source DBI is analyzed and compared with the other proposed structures. To validate the theoretical analysis, a 300-W experimental prototype is designed and tested at 25-35-V input voltage, 155 Vpeak output voltages and 50 kHz.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Optimized Control Strategy of Modular Multilevel DC Transformer for
           High-Frequency-Link Voltages Matching in the Whole Operation Range
    • Authors: Qianhao Sun;Yingdong Wei;Yu Wang;Jie Sun;Qing Mu;Xing Zhang;Jingwei Meng;Yalou Li;
      Pages: 1714 - 1727
      Abstract: High-frequency modular multilevel dc transformer (MDCT) plays an important role in the voltage conversion and power transmission for medium-voltage direct-current (MVdc) power networks application. For MDCT, when high-frequency-link (HFL) voltage amplitudes do not match the HFL transformer ratio, the increase in HFL reactive power and the decrease in efficiency become a bottleneck for its application. To solve this problem, a modified MDCT (M2DCT) is analyzed, and a HFL voltage optimized control (HVOC) for M2DCT is proposed in this paper. Different from the conventional phase shift strategies, the proposed HVOC adjusts the HFL voltage amplitudes by varying the pulsewidth of modulation wave for power switches in submodule (SM), ensuring HFL voltage amplitudes match the HFL transformer ratio in the whole operation range, reducing the HFL reactive power, and improving the efficiency of M2DCT. In addition, the soft switching is achieved in the whole operation range under HVOC. The detailed control method, architecture, SM voltages balancing algorithm, and switching characteristics of HVOC are discussed, and the influences on power transmission capacity, HFL power factor, operating efficiency of M2DCT under HVOC, and conventional HFL phase shift controls are analyzed comparatively. The experimental results verify the correctness and effectiveness of the analysis and proposed strategy.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Vector Control Strategy to Eliminate Active Power Oscillations in
           Four-Leg Grid-Connected Converters Under Unbalanced Voltages
    • Authors: Andrés Mora;Roberto Cárdenas;Matías Urrutia;Mauricio Espinoza;Matías Díaz;
      Pages: 1728 - 1738
      Abstract: The problems associated with active power oscillations (APOs) in grid-connected converters are well-known. Imbalances in the grid usually produce double-frequency oscillations in the dc-link voltage and current which could reduce the useful life of solar panels, batteries, and capacitors connected to this point. Moreover, as reported in the literature, double-frequency reactive power oscillations (RPOs) also produce adverse effects in distribution systems, and it is desirable to eliminate or mitigate them. When a four-leg power converter is connected to an unbalanced grid, the zero-sequence current provides extra degrees of freedom to compensate or even eliminate the power oscillations at the converter dc-link side. In this paper, a new methodology to regulate these double-frequency power components is proposed. It is based on a closed-loop vector control approach, where the active power oscillations (APOs) at converter side are transformed into a synchronous frame rotating at twice the grid frequency and regulated using the zero-sequence current. To avoid overcurrent produced by the circulation of positive-, negative-, and zero-sequence components a current limiter is also proposed in this paper. Experimental results obtained with a 4-kW four-leg power converter prototype are presented and discussed in this paper.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Multicell Schemes for Active-Switched-Capacitor and
           Active-Switched-Capacitor/Switched- Inductor Quasi-Z-Source Inverters
    • Authors: Rehan Majeed;Aamir Hussain Chughtai;
      Pages: 1739 - 1754
      Abstract: This paper proposes two new multicell schemes for active-switched-capacitor quasi-Z-source inverter (ASC-qZSI) and ASC/switched-inductor-qZSI topologies. Detailed theoretical models for the proposed schemes are developed. Moreover, extensive performance comparison with several existing active and passive qZSI topologies is presented. Appropriate simulations and experimental studies have been carried out, which verify the theoretical proposals. It is concluded that the proposed topologies can be useful in practical applications requiring large dc-ac voltage gain, for example, in renewable systems with low-voltage sources such as photovoltaics or fuel cells.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Multicell-to-Multicell Equalizers Based on Matrix and Half-Bridge LC
           Converters for Series-Connected Battery Strings
    • Authors: Yunlong Shang;Qi Zhang;Naxin Cui;Bin Duan;Zhongkai Zhou;Chenghui Zhang;
      Pages: 1755 - 1766
      Abstract: Due to the low switching loss, compact size, and low price, the LC series resonant converter (LCSRC) as an energy carrier is promising in battery equalizers. However, the conventional equalizers based on LCSRC only can realize the one-cell-to-one-cell balancing for a high-voltage series-connected battery pack, causing a low equalizing speed and efficiency. Therefore, two direct multicell-to-multicell (MC2MC) balancing topologies based on matrix LC converter and half-bridge LC converter are proposed, respectively, which achieve the direct energy transfer from a consecutive more-charged-cell group to a consecutive less-charged-cell group, significantly improving the equalizing speed and efficiency. An analytical model for the LCSRC is developed to provide a guidance for the optimal design of the proposed equalizers. The prototypes for the proposed two balancing topologies are constructed. The MC2MC balancing performances are verified though the comparative experimental results at different initial voltage distributions. In particular, the proposed equalizers simultaneously achieve the fast balancing speed and high equalization efficiency. The measured peak efficiency is about 87.9% at the four-cell-to-four-cell equalization.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Single-Stage Interleaved Resonant Bridgeless Boost Rectifier with
           High-Frequency Isolation
    • Authors: Guangdi Li;Jin Xia;Kun Wang;Yan Deng;Xiangning He;Yousheng Wang;
      Pages: 1767 - 1781
      Abstract: This paper proposes a novel single-phase single-stage ac-dc converter with high-frequency isolation and power factor correction. Unlike the two-stage ac-dc converters, the high-frequency pulsating voltage is obtained directly from the power factor correction semistage and is applied directly to the dc-dc semistage. The proposed topology is designed to be operated in the continuous conduction mode (CCM), and therefore, there is no need for additional input filter. In addition, the interleaving operation helps reducing the current stress and gets a better electro-magnetic interference performance. Moreover, all of the power switches in the proposed topology can achieve soft-switching commutation. Furthermore, the intermediate dc-link capacitor is no longer directly connected to the dc-dc stage and the capacitance can be reduced greatly; therefore, the bulk capacitor is replaced by a film capacitor. Frequency characteristics and time-domain analysis of the LLC resonant tank is presented in this paper to analyze the characteristics of the proposed converter. Finally, a prototype that converts universal input voltage ranging from 110 to 220 V into 400-V dc output was built and tested to verify the analysis.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Three-Phase Single-Stage AC–DC Wireless-Power-Transfer Converter With
           Power Factor Correction and Bus Voltage Control
    • Authors: Junwei Liu;Wenzheng Xu;Ka Wing Chan;Ming Liu;Xian Zhang;Nelson Hon Lung Chan;
      Pages: 1782 - 1800
      Abstract: Wireless power transfer (WPT) technology has been a research and industrial hotspot with applications in many areas, such as wireless electric vehicle charging system that requires high power, high efficiency, and high power factor (PF). Usually, the power is drawn from a 50/60 Hz single-phase or three-phase ac power source. For a high power application, a three-phase ac source is commonly used. In this paper, a three-phase single-stage WPT resonant converter with PF correction (PFC) and bus voltage control is proposed to improve efficiency and power quality of three-phase input and reduce production cost and complexity for a high power WPT system. A T-type topology is applied as the common part to perform both the PFC and dc-dc WPT functionalities simultaneously. The proposed converter is much more advantageous than a conventional three-phase two-stage WPT converter with individual PF corrector. In addition, three-phase single-stage topologies have better power quality than single-phase single-stage topologies because zero-sequence components can be naturally eliminated.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Power Stabilization With Double Transmitting Coils and T-Type Compensation
           Network for Dynamic Wireless Charging of EV
    • Authors: Shufan Li;Lifang Wang;Yanjie Guo;Chengxuan Tao;Li Ji;
      Pages: 1801 - 1812
      Abstract: Power fluctuation caused by the movement of the receiver has always been a difficult problem for the development of dynamic wireless charging of electric vehicles (EVs). A segmented dynamic wireless charging system (DWCS) based on double transmitting coils and T-type compensation network is presented in this paper to restrain the power fluctuation. Cross-coupling effects are removed by adding switches in series with the transmitting coils. A genetic algorithm based multiobject optimization for the power fluctuation factor (PFF) and the reactive component is used to design the parameters of the T-type network. Simulations show that the optimization of the T-type network is not limited to a certain structure of the transmitter and receiver coils but can minimize the PFF for different values of the gap between the transmitting coils. Experiments for separated and overlapped transmitting coils show that the proposed double-transmitting-coil power supply scheme T-type network can maintain the power fluctuation less than 6% of the average output power with the dc-dc efficiency above 85%.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Self-Oscillating Pulsewidth Modulation for Inductive Power Transfer
           Systems
    • Authors: Alireza Namadmalan;
      Pages: 1813 - 1820
      Abstract: This paper presents a new self-oscillating tuning loop for inductive power transfer (IPT) systems using a combination of phase shift and pulsewidth modulations (PS-PWMs). Self-oscillating methods are the uncertainty-tolerant solution for power and frequency control of resonant converters. However, constant duty-cycle operation affects their effectiveness with extra dc-link current ripples and losses. In this paper, PS-PWM is achieved by instant phase displacement controlling between the two legs of the inverter, which guarantees zero voltage switching (ZVS) for transients and light-load conditions. The presented solution simultaneously integrates PWM and PS switching methods with a fast dynamic response even under nonlinear conditions, e.g., battery loads, and sudden load changes. In the presented work, an optically controlled phase shifter is proposed, which has a simple structure and smoother phase regulation in comparison with digital potentiometers. Moreover, this paper analyzes the behavior of the proposed method in bifurcation condition and shows the reliability and stable operating area of the system. To show the feasibility of the presented switching technique, a prototype is implemented based on series-series (SS)-compensated topology and investigated for different operating frequencies and loads.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Guest Editorial: Special Section on Complex Vector Theory and Its
           Application in Power Electronic Systems
    • Authors: Lennart Harnefors;Xiongfei Wang;
      Pages: 1821 - 1823
      Abstract: Complex space vectors have for decades proven their usefulness for modeling, analysis, and control design in electric power engineering. One fundamental benefit is that they allow two variables—the d and q components of the vector—to be expressed in a single-input–single-output (SISO) notation. Symmetric three-phase systems and dynamic elements can be modeled using complex-coefficient transfer functions. Various extensions, primarily the corresponding two-row real space vectors and two-by-two transfer function matrices—giving a multi-input–multi-output (MIMO) model—allow asymmetric systems and elements to be modeled as well.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Complex State Variables as Analytical Tool for Control System Design of
           Medium-Voltage Drives
    • Authors: Joachim Holtz;
      Pages: 1824 - 1832
      Abstract: Complex state variables are used to analyze the dynamics of medium-voltage drives. These operate at low switching frequency to reduce the dynamic losses of the power semiconductor devices. It results in a low sampling rate of the digital signal processing system, causing signal delays that deteriorate the dynamic behavior. Undesired cross-coupling results between the current components id and iq. The effect is shown to be even more adverse than described by the conventional control theory. The solution is modeling the system by single-complex state variables. These permit designing a current controller of high dynamic performance, which exhibits zero cross-coupling. Improved performance at very low switching frequency is demonstrated by experimental results.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Enhanced Complex Space Vector Modeling and Control System Design of
           Multiphase Magnetically Levitated Rotary–Linear Machines
    • Authors: Spasoje M. Mirić;Rosario V. Giuffrida;Dominik Bortis;Johann W. Kolar;
      Pages: 1833 - 1849
      Abstract: Rotary-linear electric machines can perform coupled rotary and linear motion. In addition, they can have magnetic bearings (MBs) integrated and magnetically coupled with the rotary, linear, or rotary-linear machine operation. Since rotary-linear machines with MBs have not been thoroughly analyzed in the literature, the models that provide understanding of their operation and give basis for the control system implementation are not entirely covered. Hence, in this article, an enhanced complex space vector-based model of the rotary-linear machine with MBs is derived and expressions for the torque, thrust force, and MB force are given. The rotary-linear machine complex space vector of the voltage, current, or flux linkage is defined using the proposed transformation with two complex frames: one related to the rotation and MBs and another to the linear motion. This results in complex space vectors with two complex units; however, the techniques used for a conventional complex space vector calculation can also be applied to the proposed complex space vector description. This is also experimentally validated on a hardware prototype of a magnetically levitated linear tubular actuator (MALTA), whose position control system is designed and implemented based on the enhanced space vector modeling approach, with the dynamic operation of the MALTA, including linear motor operation with an axial stroke of 10mm and a mechanical frequency of 17Hz.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Synchronous Electrostatic Machine Torque Modulation via Complex Vector
           Voltage Control With a Current Source Inverter
    • Authors: Aditya N. Ghule;Peter Killeen;Daniel C. Ludois;
      Pages: 1850 - 1857
      Abstract: Advances in electrostatic machine design have enhanced the torque density of macroscale electrostatic machines toward practical use. A recently developed fractional horsepower three-phase separately excited synchronous electrostatic machine (SEM) demonstrates torque densities comparable to those of air-cooled permanent-magnet-based electromagnetic machines (1.5 Nm/kg) when excited with a medium voltage (5 kV). SEMs develop torque from voltage, not from current, and therefore incur nearly zero losses at low speeds or stall. However, there is no off-the-shelf medium-voltage drive at this power level, and the appropriate control framework for these machines has yet to be established. This article presents a complex vector voltage regulator control approach as a means for modulating torque in an SEM. Ampere-second (charge) is sourced from a current source inverter (CSI) serving as the drive electronics for voltage regulation. Together, the control approach and the CSI hardware form the first high-performance electrostatic drive. Key research outcomes include the theoretical development and experimental verification of charge-oriented control via voltage regulation. Experimental results are presented for rotational and stall conditions, which are reflective of the “position and hold” applications suited to electrostatic machines. The dynamic performance of the voltage regulator is verified by measuring the controller frequency response function, dynamic stiffness, and command tracking on a separately excited SEM.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Integrated Control of a Motor/Generator Set Composed of Doubly Fed
           Induction Machines
    • Authors: Marc Bodson;Md Abid Hossain;
      Pages: 1858 - 1869
      Abstract: This article considers the control problem for a motor/generator set, where a prime mover drives a generator and the electrical power produced drives a motor. Both the generator and the motor are assumed to be doubly fed induction machines with direct ac connection between their stators. The rotors are controlled by three-phase converters, so that operation is possible with motor and generator speeds that are different from each other, and not synchronized with the electrical frequency of the stator voltages. The strong couplings between the two machines motivate the design of an integrated controller. This article proposes a general framework for such a design based on a joint model of the two machines. A specific method is also developed for the control of the stator voltages and the motor velocity. In its simplest form, the proposed algorithm does not rely on current sensors. A current command option is also developed that ensures closer tracking and limiting of the rotor currents. The algorithm is relatively simple and all its parameters can be computed based on the estimates of the machine parameters. Practical implementation and testing can be performed rapidly. Experiments performed on a small-scale laboratory testbed show very good tracking performance of a speed reference profile.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • A Novel Repetitive Controller Assisted Phase-Locked Loop with
           Self-Learning Disturbance Rejection Capability for Three-Phase Grids
    • Authors: Mi Tang;Stefano Bifaretti;Sabino Pipolo;Shafiq Odhano;Pericle Zanchetta;
      Pages: 1870 - 1879
      Abstract: The synchronization between the power grid and distributed power sources is a crucial issue in the concept of smart grids. For tracking the real-time frequency and phase of threephase grids, phase-locked loop (PLL) technology is commonly used. Many existing PLLs with enhanced disturbance/harmonic rejection capabilities, either fail to maintain fast response or are not adaptive to grid frequency variations or have high computational complexity. This article, therefore, proposes a low computational burden repetitive controller (RC) assisted PLL (RCA-PLL) that is not only effective on harmonic rejection but also has remarkable steady-state performance while maintaining fast dynamic. Moreover, the proposed PLL is adaptive to variable frequency conditions and can self-learn the harmonics to be canceled. The disturbance/harmonic rejection capabilities together with dynamic and steady-state performances of the RCA-PLL have been highlighted in this article. The proposed approach is also experimentally compared to the synchronous rotation frame PLL (SRF-PLL) and the steady-state linear Kalman filter PLL (SSLKF-PLL), considering the effect of harmonics from the grid-connected converters, unbalances, sensor scaling errors, dc offsets, grid frequency variations, and phase jumps. The computational burden of the RCA-PLL is also minimized, achieving an experimental execution time of only 12 μs.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Control Design and Stability Analysis of Power Converters: The MIMO
           Generalized Bode Criterion
    • Authors: Javier Samanes;Andoni Urtasun;Ernesto L. Barrios;David Lumbreras;Jesús López;Eugenio Gubia;Pablo Sanchis;
      Pages: 1880 - 1893
      Abstract: Three-phase dynamic systems and multiphase generators are frequently modeled and controlled in the synchronous reference frame. To properly model the cross-coupling terms in this reference frame, complex vector theory and transfer function matrices are commonly applied, obtaining multiple-input multiple-output (MIMO) dynamic models. The stability of MIMO systems can be assessed through the Nyquist generalized stability criterion. However, the use of the Nyquist diagram complicates the controller design. The Bode diagram is a more intuitive tool for the controller design; however, the Bode stability criterion is not applicable to MIMO systems. In this article, the MIMO generalized Bode criterion is proposed. Since this stability criterion is based on the Nyquist generalized stability criterion, it can be applied to any system. Furthermore, it is simple to use, as it only requires information contained in the open-loop transfer matrix and the Bode diagram. The proposed stability criterion thus offers an interesting tool for the controller design procedure in MIMO systems, as it is shown in this article for two common applications: the current control loop of a power converter, a 2 × 2 system, and the current control loop of two independent power converters in parallel, a 4 × 4 system.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Analysis of STATCOM Small-Signal Impedance in the Synchronous
           d-q Frame
    • Authors: Chi Li;Rolando Burgos;Bo Wen;Ye Tang;Dushan Boroyevich;
      Pages: 1894 - 1910
      Abstract: Small-signal model impedances of grid-tied converters have recently attracted researchers' attention and have shown great importance in stability analysis. This article proposes an impedance model in d-q frame for static synchronous compensators (STATCOMs), including dynamics from synchronization, current, voltage loops, and QV droop and reveals the significant features compared to other types of grid-tied converters that: 1) impedance matrix strongly coupled in d and q channel due to nearly zero power factor; 2) different behaviors of impedances at low frequency due to inversed direction of reactive power; and 3) coupled small-signal propagation paths on the voltage at point of common coupling (PCC) from synchronization and ac voltage regulation. All these characteristics render difficulty in identifying instability patterns using existing knowledge and pinpointing the main contributor to instability among control loops, which was discussed and solved in this article. To better understand the frequency coupling effects of STATCOMs, the d-q frame impedance model was further transformed in its complex matrix form. An example of possible instability with STATCOMs was presented and analyzed using the proposed model. The impedance model was verified experimentally with a scaled-down STATCOM prototype.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Asymmetric Complex-Vector Models With Application to VSC–Grid
           Interaction
    • Authors: Lennart Harnefors;Xiongfei Wang;Shih-Feng Chou;Massimo Bongiorno;Marko Hinkkanen;Mikko Routimo;
      Pages: 1911 - 1921
      Abstract: The properties of complex space-vector models for asymmetric three-phase systems are investigated in this article. Most importantly, three alternative methods for the stability analysis of the asymmetric closed-loop systems are presented. The end results avoid the usage of matrix manipulations. It is shown how the theory can be applied to modeling and stability analysis of a grid-connected voltage-source converter (VSC). The methods are compared using numerical examples.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Stationary-Frame Complex-Valued Frequency-Domain Modeling of Three-Phase
           Power Converters
    • Authors: Yicheng Liao;Xiongfei Wang;
      Pages: 1922 - 1933
      Abstract: The stationary-frame complex-valued frequency-domain modeling has been applied to characterize the frequency-coupling dynamics of three-phase converters. Yet, those models are generally derived through mathematical transformations of the linearized time-invariant models in the rotating dq-frame. A step-by-step modeling method with clear physical insight in the stationary frame is still missing. This article attempts to fill in the void by introducing a general stationary (αβ)-frame, three-port equivalent circuit model for the converter power stage, based on the direct linearization around time-periodic trajectories. The model not only reveals the frequency-coupling effect of the ac-dc dynamic interaction but also provides an explicit theoretical basis for incorporating the control dynamics. Moreover, the dependence of the frequency-coupling terms on the initial phase of the input voltage is pointed out. Considering the phase-dependent feature, a frequency scan method that can accurately measure the αβ-frame converter model is proposed. The measured frequency responses in both the nonlinear time-domain simulations and experimental tests validate the effectiveness of the frequency scan method and the theoretical analysis.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Complex-Valued Multifrequency Admittance Model of Three-Phase VSCs in
           Unbalanced Grids
    • Authors: Yicheng Liao;Xiongfei Wang;Xiaolong Yue;Lennart Harnefors;
      Pages: 1934 - 1946
      Abstract: This article proposes a multifrequency admittance model for voltage-source converters with three-phase unbalanced grid voltages. The model is derived with multiple complex vectors and harmonic transfer functions, which is merely dependent on its own input voltage trajectory, and can accurately capture the frequency-coupling dynamics. The dynamic effects of both the basic synchronous-reference-frame phase-locked loop (PLL) and its alternative with a notch filter of the negative-sequence voltage component are compared. It is revealed that the notch-filtered PLL significantly weakens the frequency-coupling effects, which leads to a reduced order of the admittance model. The developed model is validated by a frequency scan, and the frequency-coupling effects impacted by different PLLs and voltage unbalance factors are verified by the experimental tests. Finally, a case study on stability analysis in unbalanced grids proves the significance of the model.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Dynamic Impact of Zero-Sequence Circulating Current on Modular Multilevel
           Converters: Complex-Valued AC Impedance Modeling and Analysis
    • Authors: Heng Wu;Xiongfei Wang;
      Pages: 1947 - 1963
      Abstract: The stability impacts of the internal control dynamics of the modular multilevel converters (MMCs) have been discussed recently. Yet, the impact of zero-sequence circulating-current (ZSCC) dynamics on the ac-side dynamics of the MMCs is hitherto unaddressed. This article develops the ac impedance model for the grid-connected MMCs by means of complex vectors and harmonic transfer-function matrices, which allows separately characterizing the dynamics of the ZSCC. Then, based on the complex-valued model, a single-input-single-output closed-loop equivalent impedance is derived for grid-connected MMCs, considering both the frequency-coupling dynamics of the MMCs and the interactions with the grid impedance, which enables a design-oriented analysis on the stability impact of the ZSCC. It is revealed that the resonant peaks in the ac impedance of the MMC are yielded due to the absence of the ZSCC control, which tends to destabilize the system in weak grids. A systematic parameter-tuning method of the ZSCC control loop is developed to guarantee the system stability. Case studies in time-domain simulations corroborate the theoretical analysis.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
  • Proceedings of the IEEE
    • Pages: 1964 - 1964
      Abstract: Advertisement.
      PubDate: June 2020
      Issue No: Vol. 8, No. 2 (2020)
       
 
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