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  Subjects -> ELECTRONICS (Total: 152 journals)
Advances in Biosensors and Bioelectronics     Open Access   (Followers: 1)
Advances in Magnetic and Optical Resonance     Full-text available via subscription   (Followers: 5)
Advances in Microelectronic Engineering     Open Access   (Followers: 2)
Advances in Power Electronics     Open Access   (Followers: 8)
Aerospace and Electronic Systems, IEEE Transactions on     Hybrid Journal   (Followers: 68)
American Journal of Electrical and Electronic Engineering     Open Access   (Followers: 10)
Annals of Telecommunications     Hybrid Journal   (Followers: 4)
APL : Organic Electronics and Photonics     Hybrid Journal   (Followers: 2)
APSIPA Transactions on Signal and Information Processing     Open Access   (Followers: 6)
Archives of Electrical Engineering     Open Access   (Followers: 9)
Autonomous Mental Development, IEEE Transactions on     Hybrid Journal   (Followers: 5)
Bell Labs Technical Journal     Hybrid Journal   (Followers: 9)
Biomedical Engineering, IEEE Reviews in     Full-text available via subscription   (Followers: 16)
Biomedical Engineering, IEEE Transactions on     Hybrid Journal   (Followers: 14)
Biomedical Instrumentation & Technology     Full-text available via subscription   (Followers: 4)
Broadcasting, IEEE Transactions on     Hybrid Journal   (Followers: 5)
BULLETIN of National Technical University of Ukraine. Series RADIOTECHNIQUE. RADIOAPPARATUS BUILDING     Open Access   (Followers: 1)
Bulletin of the Polish Academy of Sciences : Technical Sciences     Open Access  
Canadian Journal of Remote Sensing     Full-text available via subscription   (Followers: 13)
China Communications     Full-text available via subscription   (Followers: 4)
Circuits and Systems     Open Access   (Followers: 9)
Consumer Electronics Times     Open Access   (Followers: 4)
Control Systems     Hybrid Journal   (Followers: 22)
Electronic Markets     Hybrid Journal   (Followers: 5)
Electronic Materials Letters     Hybrid Journal   (Followers: 3)
Electronics     Open Access   (Followers: 7)
Electronics and Communications in Japan     Hybrid Journal   (Followers: 5)
Electronics Letters     Hybrid Journal   (Followers: 19)
Embedded Systems Letters, IEEE     Hybrid Journal   (Followers: 20)
Energy Harvesting and Systems : Materials, Mechanisms, Circuits and Storage     Hybrid Journal   (Followers: 1)
EPJ Quantum Technology     Open Access  
EURASIP Journal on Embedded Systems     Open Access   (Followers: 8)
Facta Universitatis, Series : Electronics and Energetics     Open Access  
Foundations and TrendsĀ® in Communications and Information Theory     Full-text available via subscription   (Followers: 6)
Foundations and TrendsĀ® in Signal Processing     Full-text available via subscription   (Followers: 4)
Frequenz     Full-text available via subscription   (Followers: 2)
Frontiers of Optoelectronics     Hybrid Journal   (Followers: 2)
Geoscience and Remote Sensing, IEEE Transactions on     Hybrid Journal   (Followers: 21)
Haptics, IEEE Transactions on     Hybrid Journal   (Followers: 4)
IEEE Antennas and Propagation Magazine     Hybrid Journal   (Followers: 15)
IEEE Antennas and Wireless Propagation Letters     Hybrid Journal   (Followers: 14)
IEEE Consumer Electronics Magazine     Full-text available via subscription   (Followers: 16)
IEEE Journal of Emerging and Selected Topics in Power Electronics     Hybrid Journal   (Followers: 10)
IEEE Journal of the Electron Devices Society     Open Access   (Followers: 2)
IEEE Power Electronics Magazine     Full-text available via subscription   (Followers: 6)
IEEE Transactions on Antennas and Propagation     Full-text available via subscription   (Followers: 10)
IEEE Transactions on Audio, Speech, and Language Processing     Hybrid Journal   (Followers: 12)
IEEE Transactions on Automatic Control     Hybrid Journal   (Followers: 23)
IEEE Transactions on Consumer Electronics     Hybrid Journal   (Followers: 16)
IEEE Transactions on Electron Devices     Hybrid Journal   (Followers: 7)
IEEE Transactions on Information Theory     Hybrid Journal   (Followers: 14)
IEEE Transactions on Power Electronics     Hybrid Journal   (Followers: 17)
IEICE - Transactions on Electronics     Full-text available via subscription   (Followers: 8)
IEICE - Transactions on Information and Systems     Full-text available via subscription   (Followers: 7)
IET Microwaves, Antennas & Propagation     Hybrid Journal   (Followers: 7)
IET Power Electronics     Hybrid Journal   (Followers: 10)
IET Wireless Sensor Systems     Hybrid Journal   (Followers: 7)
IETE Journal of Education     Open Access   (Followers: 2)
IETE Journal of Research     Open Access   (Followers: 9)
IETE Technical Review     Open Access   (Followers: 4)
Industrial Electronics, IEEE Transactions on     Hybrid Journal   (Followers: 12)
Industry Applications, IEEE Transactions on     Hybrid Journal   (Followers: 5)
Informatik-Spektrum     Hybrid Journal  
Instabilities in Silicon Devices     Full-text available via subscription  
Intelligent Transportation Systems Magazine, IEEE     Full-text available via subscription   (Followers: 1)
International Journal of Advanced Electronics and Communication Systems     Open Access   (Followers: 5)
International Journal of Advanced Research in Computer Science and Electronics Engineering     Open Access   (Followers: 20)
International Journal of Advances in Telecommunications, Electrotechnics, Signals and Systems     Open Access   (Followers: 3)
International Journal of Aerospace Innovations     Full-text available via subscription   (Followers: 11)
International Journal of Antennas and Propagation     Open Access   (Followers: 8)
International Journal of Applied Electronics in Physics & Robotics     Open Access   (Followers: 1)
International Journal of Biomedical Nanoscience and Nanotechnology     Hybrid Journal   (Followers: 7)
International Journal of Computational Vision and Robotics     Hybrid Journal   (Followers: 4)
International Journal of Computer & Electronics Research     Full-text available via subscription   (Followers: 2)
International Journal of Control     Hybrid Journal   (Followers: 12)
International Journal of Electronics     Hybrid Journal   (Followers: 2)
International Journal of Electronics & Data Communication     Open Access   (Followers: 4)
International Journal of Electronics and Telecommunications     Open Access   (Followers: 3)
International Journal of Granular Computing, Rough Sets and Intelligent Systems     Hybrid Journal   (Followers: 1)
International Journal of High Speed Electronics and Systems     Hybrid Journal  
International Journal of Microwave and Wireless Technologies     Hybrid Journal   (Followers: 1)
International Journal of Nano Devices, Sensors and Systems     Open Access   (Followers: 4)
International Journal of Nanoscience     Hybrid Journal   (Followers: 1)
International Journal of Numerical Modelling:Electronic Networks, Devices and Fields     Hybrid Journal   (Followers: 2)
International Journal of Power Electronics     Hybrid Journal   (Followers: 5)
International Journal of Review in Electronics & Communication Engineering     Open Access   (Followers: 2)
International Journal of Sensors, Wireless Communications and Control     Hybrid Journal   (Followers: 2)
International Journal of Systems, Control and Communications     Hybrid Journal   (Followers: 2)
International Journal on Communication     Full-text available via subscription   (Followers: 8)
International Journal on Electrical and Power Engineering     Full-text available via subscription   (Followers: 11)
International Transaction of Electrical and Computer Engineers System     Open Access  
ISRN Electronics     Open Access   (Followers: 1)
ISRN Signal Processing     Open Access   (Followers: 1)
Journal of Advanced Dielectrics     Open Access   (Followers: 1)
Journal of Artificial Intelligence     Open Access   (Followers: 5)
Journal of Circuits, Systems, and Computers     Hybrid Journal   (Followers: 1)
Journal of Electrical and Electronics Engineering Research     Open Access   (Followers: 2)
Journal of Electrical Bioimpedance     Full-text available via subscription   (Followers: 2)
Journal of Electrical Engineering & Electronic Technology     Full-text available via subscription   (Followers: 1)
Journal of Electromagnetic Analysis and Applications     Open Access   (Followers: 5)

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  IEEE Transactions on Power Electronics
  [SJR: 3.308]   [H-I: 111]   [19 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0885-8993
   Published by Institute of Electrical and Electronics Engineers (IEEE) Homepage  [176 journals]
  • IEEE Power Electronics Society Information
    • Pages: C3 - C3
      Abstract: Provides a listing of current committee members and society officers.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Table of contents
    • Pages: C1 - C2
      Abstract: Presents the table of contents for this issue of this publication.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • IEEE Transactions on Power Electronics publication information
    • Pages: C2 - C2
      Abstract: Provides a listing of current staff, committee members and society officers.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Modified Discontinuous PWM for Size Reduction of the Circulating Current
           Filter in Parallel Interleaved Converters
    • Authors: Gohil; G.;Maheshwari, R.;Bede, L.;Kerekes, T.;Teodorescu, R.;Liserre, M.;Blaabjerg, F.;
      Pages: 3457 - 3470
      Abstract: Parallel voltage-source converters (VSCs) require an inductive filter to suppress the circulating current. The size of this filter can be minimized by reducing either the maximum value of the flux linkage or the core losses. This paper presents a modified discontinuous pulsewidth modulation (DPWM) scheme to reduce the maximum value of the flux linkage and the core losses in the circulating current filter. In the proposed PWM scheme, the dwell time of an active vector is divided within a half-carrier cycle to ensure simultaneous occurrence of the same zero vectors in both VSCs. A function to decide the ratio of the dwell time of the divided active vector is also presented. The effect of the proposed PWM scheme on the maximum value of the flux linkage and the core losses is analyzed and compared with that of the space vector modulation and 60 $^circ$ clamped DPWM schemes. The analytical expressions for the maximum value of the flux linkage are derived for each of these PWM schemes. In addition, the effect of the proposed PWM scheme on the line current ripple and the switching losses is also analyzed and compared. To verify the analysis, experimental results are presented, which prove the effectiveness of the proposed PWM scheme.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Seventeen-Level Inverter Formed by Cascading Flying Capacitor and Floating
           Capacitor H-Bridges
    • Authors: Kumar; P.R.;Kaarthik, R.S.;Gopakumar, K.;Leon, J.I.;Franquelo, L.G.;
      Pages: 3471 - 3478
      Abstract: A multilevel inverter for generating 17 voltage levels using a three-level flying capacitor inverter and cascaded H-bridge modules with floating capacitors has been proposed. Various aspects of the proposed inverter like capacitor voltage balancing have been presented in the present paper. Experimental results are presented to study the performance of the proposed converter. The stability of the capacitor balancing algorithm has been verified both during transients and steady-state operation. All the capacitors in this circuit can be balanced instantaneously by using one of the pole voltage combinations. Another advantage of this topology is its ability to generate all the voltages from a single dc-link power supply which enables back-to-back operation of converter. Also, the proposed inverter can be operated at all load power factors and modulation indices. Additional advantage is, if one of the H-bridges fail, the inverter can still be operated at full load with reduced number of levels. This configuration has very low dv/dt and common-mode voltage variation.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • PV Balancers: Concept, Architectures, and Realization
    • Authors: Zhou; H.;Zhao, J.;Han, Y.;
      Pages: 3479 - 3487
      Abstract: This paper presents a new concept of module-integrated converters called PV balancers for photovoltaic applications. The proposed concept enables independent maximum power point tracking for each module, and dramatically decreases the requirements in terms of electrical rating, size, and manufacturing cost for power converters. The power rating of a PV balancer is less than 20% of its counterparts, and the manufacturing cost is thus significantly reduced. In this paper, two architectures of PV balancers are proposed, analyzed, realized, and verified through simulation and experimental results. It is anticipated that the proposed approach will be a low-cost solution for future photovoltaic power systems.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Reference-Trajectory-Optimized SVM for High-Power Current-Source
    • Authors: Hu; A.;Xu, D.D.;Wu, B.;Wang, J.;Su, J.;
      Pages: 3488 - 3498
      Abstract: For medium-voltage high-power drives fed by current-source converters (CSCs), a transformerless configuration has benefits in both cost and volume. Removing the isolation transformer necessitates a common-mode choke to undertake the major portion of the drive's common-mode voltage (CMV) stress, which would otherwise cause premature failure of the motor insulation system. On the other hand, as device switching frequency in high-power CSCs is normally limited to a few hundred hertz, improving harmonic performance via modulation has always been a challenge. Selective harmonic elimination (SHE) is a preferred modulation scheme in such a system owing to its ability to eliminate several unwanted low-order harmonic currents. Alternatively, conventional space vector modulation (SVM) provides continuous modulation index adjustment capability, but its output current contains low-order harmonics with high magnitudes that may arouse harmful resonances in the system. Aiming at reducing CMV and improving harmonic performance at the same time, this paper proposes a new SVM-based modulation strategy for high-power CSCs using synthesized reference trajectory on the hexagon in the αβ plane. Along with the proposed strategy, two methods of reference trajectory optimization (RTO) are investigated. By introducing a coefficient to the duty-cycle function for RTO, the first method can remove an extra low-order harmonic component, or minimize the weighted total harmonic distortion. The second method, with a different approach of RTO, eliminates the unwanted low-order harmonics by combining the proposed SVM with the SHE. The proposed concepts are verified by both simulation and experimental results.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Three-Level DC Converter for Balancing DC 800-V Voltage
    • Authors: Zhang; X.;Gong, C.;Yao, Z.;
      Pages: 3499 - 3507
      Abstract: This paper studies a three-level dc converter for balancing the dc input voltage, which has a similar topology with the conventional three-level dc converter. It can easily build a neutral line for changing a dc voltage source into two dc voltage-level sources. A control strategy of conducting time extension of partial switch devices is also presented for achieving three-level states of each power switch. The operating principle of the converter is analyzed in detail based on the presented control strategy. The small-signal model and the effects of the proposed control strategy are also driven. Finally, a prototype is fabricated and tested in the lab and the experimental results verify the converter to achieve three-level characteristics and to have a good ability of balancing the input voltage.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Improved Selective Harmonics Elimination Scheme With Online Harmonic
           Compensation for High-Power PWM Converters
    • Authors: Zhang; Y.;Li, Y.W.;Zargari, N.R.;Cheng, Z.;
      Pages: 3508 - 3517
      Abstract: To reduce the low-order harmonics produced by the high-power pulsewidth-modulated (PWM) converters, selective harmonic elimination (SHE) scheme is commonly used due to its superior harmonic performance at low switching frequency. However, as an off-line modulation technique, the SHE scheme itself lacks the capability to realize the active compensation of the grid background harmonics. To enable the active compensation ability of the SHE-modulated PWM converters, this paper proposes an active compensation method through the jittering of SHE phase angle. The proposed method can realize the real-time compensation of the preexisting system background harmonics in high-power PWM converters’ system. An application example on a high-power PWM current-source rectifier (CSR) system is provided in this paper. Experimental results show that the proposed method can effectively attenuate the line current harmonics caused by the grid background harmonics in the high-power PWM CSR systems.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Submodule Implementation for Parallel Connection of Capacitors in
           Modular Multilevel Converters
    • Authors: Ilves; K.;Taffner, F.;Norrga, S.;Antonopoulos, A.;Harnefors, L.;Nee, H.;
      Pages: 3518 - 3527
      Abstract: In modular multilevel converters, there is a tradeoff between the switching frequency and the voltage ripple in the submodule capacitors. The reason for this is that it becomes increasingly difficult to balance the capacitor voltages when the switching frequency is reduced. This paper presents a new submodule circuit, which improves the balancing of the capacitor voltages at low switching frequencies. The proposed submodule circuit consists of two capacitors and eight switches, forming a three-level submodule. Ideally, the voltage and current ratings of the switches can be chosen such that the combined power rating of the semiconductors is the same as for the equivalent solution with conventional half-bridge submodules. The proposed submodule circuit provides the possibility of connecting the two capacitors in parallel when the intermediate voltage level is used. This will reduce the capacitor voltage ripple, especially at low switching frequencies, and thus, allow for a reduction of the size, weight, and cost of the submodule capacitors. The proposed submodule circuit is validated by both simulations and experimental results. It is found that the parallel connection of the submodule capacitors will, in fact, significantly improve the balancing of the capacitor voltages.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Modeling Bidirectional Contactless Grid Interfaces With a Soft DC-Link
    • Authors: Weearsinghe; S.;Thrimawithana, D.J.;Madawala, U.K.;
      Pages: 3528 - 3541
      Abstract: Inductively coupled, bidirectional grid interfaces are gaining popularity as an attractive solution for vehicle-to-grid (V2G) and grid-to-vehicle (G2V) systems. However, such systems conventionally employ a large, electrolytic dc-link capacitor as well as a large input inductor, leading to expensive, bulky, and less reliable systems. Although, matrix converter (MC) based bidirectional inductive power transfer (BD-IPT) grid interfaces have been proposed as an alternative, implementation of safe and reliable MCs in BD-IPT applications is still a challenge, owing to the absence of natural freewheeling paths and higher complexity. As a solution, this paper proposes a new, inductively coupled, bidirectional grid interface, without a dc-link capacitor and an input inductor, consisting of two back-to-back connected converters. In contrast to existing bidirectional grid converters, the proposed system employs a simpler switching strategy with a lower switching frequency. A mathematical model, which predicts the behavior of the introduced system, is also presented. The feasibility of the proposed technique and the accuracy of the mathematical model are demonstrated through both simulations and experimental results of a 1.1-kW prototype system.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Analysis and Suppression of Circulating Harmonic Currents in a Modular
           Multilevel Converter Considering the Impact of Dead Time
    • Authors: Chen; B.;Chen, Y.;Tian, C.;Yuan, J.;Yao, X.;
      Pages: 3542 - 3552
      Abstract: This paper focuses on analysis and suppression of circulating harmonic currents in a modular multilevel converter (MMC) considering the impact of dead time in medium-voltage applications. A continuous equivalent model of the MMC containing two ideal transformer models is presented. Using this model, the impact of a harmonic voltage upon the dc side is analyzed and the production mechanism of circulating harmonic currents is elucidated. At the same time, the impact of dead time and insulated gate bipolar transistor (IGBT) voltage drop (DTVD) is studied, which indicates that capacitor voltages, output harmonics, and circulating harmonic currents are influenced. Based on this analysis, an open-loop control strategy to suppressing circulating harmonic currents caused by the output current and DTVD is presented. Finally, all these conclusions are verified using a simulation platform with 14 modules per arm fed by a 14-kV dc voltage source and a downscaled experimental platform with four modules per arm fed by a 560-V dc voltage source.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Losses in Medium-Voltage Megawatt-Rated Direct AC/AC Power Electronics
    • Authors: Moghe; R.;Kandula, R.P.;Iyer, A.;Divan, D.;
      Pages: 3553 - 3562
      Abstract: Direct ac/ac topologies for ac-to-ac power conversion benefit from the absence of dc-link capacitors, and therefore, are highly reliable and have low cost as compared to the traditional voltage-source inverter (VSI)-based topologies. This paper deals with one of the more important tradeoffs considered in designing highly efficient converters: Losses. It is shown in this paper that the direct ac/ac converters have an inherently higher efficiency than their VSI-based back-to-back counterparts due to a dramatic reduction in switching losses (nearly 60%). Further, this paper compares the performance of three different device types (SiC MOSFETs, hybrid Si IGBT/SiC diode, and Si IGBTs) using wide-range device characterization that help to create detailed loss models. It is conjectured that traditional datasheets lack the level of detail needed for computing losses in direct ac/ac converters, and the availability of a multivalue voltage, current, and temperature-based loss profile is advocated. Using the obtained loss models, a comparison is drawn between the considered devices through simulations when operated in a 13-kV/1-MW direct ac/ac power flow controller, the controllable network transformer (CNT). The same loss-models are also used to compute losses in an experimental prototype of a 720-V, 10-kVA CNT and the results are compared with direct efficiency measurements. A similar computation is carried out for another experimental prototype at a 6.7-kV, 400-kVA, three-level, paralleled CNT. These experimental tests are used to confirm the validity of the analytical results presented in this paper.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Analysis and Mitigation of Inverter Output Impedance Impacts for
           Distributed Energy Resource Interface
    • Authors: Tao; Y.;Liu, Q.;Deng, Y.;Liu, X.;He, X.;
      Pages: 3563 - 3576
      Abstract: In order to provide reliable electric power, the interfacing voltage source inverters in distributed generation often rely on autonomous droop control method integrated with virtual impedance and inner voltage and current control loops. In general, the droop-controlled inverters can be modeled as a controllable voltage source in series with output impedance. However, stability, dynamic performance, and load adaptability in islanding mode are sensitive to the inverter output impedance. In this paper, the detailed impacts of the inverter output impedance are investigated in different operation modes. Furthermore, an inverter current feedforward control scheme is proposed to mitigate the effects. With the implementation of the proposed control scheme, system reliability and load adaptability in islanding mode are enhanced without additional control complexity and extra sensors. Moreover, a voltage magnitude control loop is added to improve the control accuracy of reactive power flow in grid-connected mode. Finally, the proposed strategy is validated with simulation and experiments based on a 15-kVA prototype.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A New Reactive Current Reference Algorithm for the STATCOM System Based on
           Cascaded Multilevel Inverters
    • Authors: Haw; L.K.;Dahidah, M.S.A.;Almurib, H.A.F.;
      Pages: 3577 - 3588
      Abstract: This paper presents a simple controller integrating a new reactive current reference algorithm for enhancing the transient performance of static synchronous compensator (STATCOM). A multilevel cascaded inverter with separated dc capacitors which is driven by carrier-based pulse width modulation is used to implement the STATCOM. The voltage across each dc-link capacitor is regulated by the rotated switching swapping scheme. In this paper, the STATCOM is controlled to provide both reactive power (VAR) compensation and grid power factor correction at the point of common coupling with a dynamically varying reactive load system. The proposed algorithm enhances the transient performance of the closed-loop system with only proportional controller and minimizes the STATCOM reactive current ripples. STATCOM based on a five-level cascaded inverter is presented in this paper and the performance of the proposed controller is investigated through various simulation studies using MATLAB/Simulink software for both steady state and transient conditions. A laboratory prototype is also developed to verify the simulation results where a good match between simulation and experimental results is achieved.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Effects of Interaction of Power Converters Coupled via Power Grid: A
           Design-Oriented Study
    • Authors: Wan; C.;Huang, M.;Tse, C.K.;Ruan, X.;
      Pages: 3589 - 3600
      Abstract: Voltage-source converters are commonly employed as rectifiers for providing a regulated dc voltage from an ac power source. In a typical microdistribution system, the power grid is nonideal and often presents itself as a voltage source with significant impedance. Thus, power converters connected to the grid interact with each other via the nonideal grid. In this paper, we study how stability can be compromised in a system of interacting grid-connected converters, which are used typically as rectifiers. Specifically, the stable operating regions in the selected parameter space may shrink when grid-connected converters interact under certain conditions. We consider the effect of both source (grid) impedance and transmission line impedance between converters, and derive bifurcation boundaries in the parameter space. A small-signal model in the dq-frame is adopted to analyze the interacting system using an impedance-based approach. It is shown that the system of interacting converters can become unstable. Moreover, results are presented in design-oriented forms so as to facilitate the identification of variation trends of stable operation boundaries. Experimental results verify the instability phenomenon.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Electric Springs for Reducing Power Imbalance in Three-Phase Power Systems
    • Authors: Yan; S.;Tan, S.;Lee, C.;Chaudhuri, B.;Hui, S.Y.R.;
      Pages: 3601 - 3609
      Abstract: Electric springs have been used previously in stabilizing mains voltage fluctuation in power grid fed by intermittent renewable energy sources. This paper describes a new three-phase electric spring circuit and its new operation in reducing power imbalance in the three-phase power system of a building. Based on government energy use data for tall buildings, the electric loads are classified as critical and noncritical loads so that building energy model can be developed. The proposed electric spring is connected in series with the noncritical loads to form a new generation of smart loads. A control scheme for such smart loads to reduce power imbalance within the building's electric power system has been evaluated initially with an experimental prototype and then in a system simulation study. The results have confirmed the effectiveness of the new three-phase electric springs in reducing power imbalance and voltage fluctuation, making the building loads adaptive to internal load changes and external mains voltage changes.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A High-Efficiency MOSFET Transformerless Inverter for Nonisolated
           Microinverter Applications
    • Authors: Chen; B.;Gu, B.;Zhang, L.;Zahid, Z.U.;Lai, J.J.;Liao, Z.;Hao, R.;
      Pages: 3610 - 3622
      Abstract: State-of-the-art low-power-level metal–oxide–semiconductor field-effect transistor (MOSFET)-based transformerless photovoltaic (PV) inverters can achieve high efficiency by using latest super junction MOSFETs. However, these MOSFET-based inverter topologies suffer from one or more of these drawbacks: MOSFET failure risk from body diode reverse recovery, increased conduction losses due to more devices, or low magnetics utilization. By splitting the conventional MOSFET-based phase leg with an optimized inductor, this paper proposes a novel MOSFET-based phase leg configuration to minimize these drawbacks. Based on the proposed phase leg configuration, a high efficiency single-phase MOSFET transformerless inverter is presented for the PV microinverter applications. The pulsewidth modulation (PWM) modulation and circuit operation principle are then described. The common-mode and differential-mode voltage model is then presented and analyzed for circuit design. Experimental results of a 250 W hardware prototype are shown to demonstrate the merits of the proposed transformerless inverter on nonisolated two-stage PV microinverter application.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Evaluation of the Performance of BTFCLs for Enhancing LVRT Capability of
    • Authors: Guo; W.;Xiao, L.;Dai, S.;Xu, X.;Li, Y.;Wang, Y.;
      Pages: 3623 - 3637
      Abstract: Performance of three kinds of bridge-type fault current limiters (BTFCLs) for enhancing low-voltage-ride-through (LVRT) capability of DFIG is evaluated in this paper. The common BTFCL can effectively enhance the LVRT capability of DFIG. However, the fault-current-limiting inductor (FCLI) is periodically inserted into the stator circuit under normal operation for compensating power losses of the FCLI. The periodically insertion of the FCLI induces stator voltage spikes, which causes significant stator flux and electromagnetic torque oscillations. One feasible way to solve this problem is to use an additional current-regulating circuit (CRC). However, the additional CRC increases hardware cost, reduces reliability of the whole system, and induces more power losses. To solve this problem, a BTFCL with bypass resistor (BTFCL-BR) is presented. The BR absorbs the majority of the current harmonics during normal operation and eliminates the stator voltage spikes. The flux and electromagnetic torque oscillations can thus be significantly reduced. The performance of three kinds of BTFCLs is evaluated by simulation and experimental studies on a typical 1.5 MW wind turbine driven DFIG system and a 2 kW DFIG prototype. By simulation and experimental evaluations, it seems that the BTFCL-BR approach is the most promising solutions among the three kinds of BTFCLs.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Novel Integration of a PV-Wind Energy System With Enhanced Efficiency
    • Authors: Wandhare; R.G.;Agarwal, V.;
      Pages: 3638 - 3649
      Abstract: A novel integration scheme of solar photovoltaic (PV) with a large capacity doubly excited induction generator-based wind energy system is described. The proposed scheme uses both the grid- and rotor-side power converters of doubly fed induction generator to inject PV power into the grid. Thus, it renders a cost-effective solution to PV-grid integration by obviating the need for a dedicated converter for PV power processing. The system is able to feed significantly large PV power into the grid compared to an equivalent rating inverter used in the conventional PV-grid system. The proposed scheme prevents circulating power during subsynchronous operation during the availability of solar radiation. All these features enhance system efficiency. System stability is also augmented due to turbine inertia, facilitating high PV penetration into the power grid. The intermittent but complementary nature of solar PV and wind energy sources considerably improves the converters’ utilization. Besides, the proposed scheme does not hamper maximum power point tracking of PV and wind sources except during very rarely occurring environmental glitches, which the PV power control algorithm is suitably geared to handle. A comprehensive system model is presented and used for designing the control strategy. The proposed scheme is supported by analysis, simulations, and experiments on a laboratory prototype.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Independent Operation of DFIG-Based WECS Using Resonant Feedback
           Compensators Under Unbalanced Grid Voltage Conditions
    • Authors: Nian; H.;Cheng, P.;Zhu, Z.Q.;
      Pages: 3650 - 3661
      Abstract: This paper presents an independent operation of the rotor-side converter (RSC) and grid-side converter (GSC) for a doubly fed induction generator (DFIG)-based wind energy conversion system under unbalanced grid voltage conditions. In this paper, the RSC is controlled to achieve four different control targets, including balanced stator current, sinusoidal rotor current, smooth stator active and reactive powers, and constant DFIG electromagnetic torque. The GSC is commanded to keep the dc voltage at a constant value. Additional feedback compensators using resonant regulators for the RSC are employed, and the decompositions of the positive and negative sequence components and calculations of the rotor negative current references can be avoided. Another similar compensator is used in the GSC to suppress the dc voltage fluctuates and remove the GSC reactive power oscillations without the stator or rotor power information. The proposed method can make the RSC and GSC available to an independent operation with a simple implementation for higher reliability. The experimental results demonstrate the effectiveness of the proposed control strategy for both the RSC and GSC under unbalanced grid voltage conditions.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Single-Phase Rectifier Having Two Independent Voltage Outputs With
           Reduced Fundamental Frequency Voltage Ripples
    • Authors: Ming; W.;Zhong, Q.;
      Pages: 3662 - 3673
      Abstract: Half-bridge rectifiers are able to provide two voltage outputs, which offers three voltage levels, but the two voltage outputs depend on each other and also on system parameters. Moreover, the two voltage outputs contain large ripples because the currents following through the split capacitors contain significant fundamental-frequency components. In this paper, after analyzing the drawbacks of half-bridge rectifiers in detail, an independently controlled neutral leg is added to conventional half-bridge rectifiers to address these drawbacks. Furthermore, the associated decoupling control strategies are proposed. The rectification leg from the conventional half-bridge rectifier is controlled to maintain the dc-bus voltage and to draw a clean sinusoidal current that is in phase with the supply voltage. The neutral leg is controlled with a PI-repetitive controller to regulate one voltage output and also to provide the current path for any dc and/or fundamental-frequency components. As a result, the two voltage outputs are regulated independently and are robust against system parameters. The output voltage ripples are also reduced, and hence, the required capacitance to achieve the same level of voltage ripples is reduced. Experimental results are provided to validate the performance of the proposed single-phase rectifiers having two independent voltage outputs.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Multilevel Medium-Frequency Link Inverter for Utility Scale Photovoltaic
    • Authors: Essakiappan; S.;Krishnamoorthy, H.S.;Enjeti, P.;Balog, R.S.;Ahmed, S.;
      Pages: 3674 - 3684
      Abstract: A multilevel topology with medium-frequency ac link for medium-voltage grid integration of utility photovoltaic (PV) plants is discussed in this paper. A megawatt-scale PV plant is divided into many zones, each comprising of two series-connected arrays. Each zone employs a medium-frequency transformer with three secondaries, which interface with the three phases of the medium voltage grid. An insulated-gate bipolar transistor full-bridge inverter feeds the MF transformer. The voltages at the transformer secondaries are then converted to three-phase line frequency ac by three full-bridge ac–ac converters. Second line frequency harmonic power does not appear in the dc bus, thereby reducing the dc capacitor size. Cascading several such cells, a high-quality multilevel medium-voltage output is generated. A new control method is proposed for the cascaded multilevel converter during partial shading while minimizing the switch ratings. The proposed topology eliminates the need for line frequency transformer isolation and reduces the dc bus capacitor size, while improving the power factor and energy yield. This paper presents the analysis, design example, and operation of a 10-MW utility PV system with experimental results on a scaled-down laboratory prototype.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Steady-State Analysis and Design of Class-DE Inverter at Any Duty Ratio
    • Authors: Sekiya; H.;Wei, X.;Nagashima, T.;Kazimierczuk, M.K.;
      Pages: 3685 - 3694
      Abstract: This paper presents a steady-state analysis and design equations for the class-DE inverters at any duty ratio and high loaded quality factor, taking into account nonlinear MOSFET drain–source and gate–drain parasitic capacitances with any grading coefficients of the diode junctions. Additionally, maximum operating frequency, power output capability, and power-conversion efficiency of the class-DE inverter are also obtained. It is shown that the maximum operating frequency is the highest when the switch-on duty ratio is 0.25. From the obtained results, it can be stated that the switch-on duty ratio of the class-DE inverter should be specified in the range of $displaystyle 0.25 le D < 0.5$ .
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A New Interleaved Three-Phase Single-Stage PFC AC–DC Converter With
           Flying Capacitor
    • Authors: Narimani; M.;Moschopoulos, G.;
      Pages: 3695 - 3702
      Abstract: A new interleaved three-phase PFC ac–dc single-stage multilevel is proposed in this paper. The proposed converter can operate with reduced input current ripple and peak switch currents due to its interleaved structure, a continuous output inductor current due to its three-level structure, and improved light-load efficiency as some of its switches can be turned ON softly. In the paper, the operation of the converter is explained, the steady-state characteristics of the new converter are determined, and its design is discussed. The feasibility of the new converter is confirmed with experimental results obtained from a prototype converter, and its efficiency is compared to that of another multilevel converter of similar type.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Embedded Control of n-Level DC–DC–AC
    • Authors: Reddy, B.D.;N.K; A.;Selvan, M.P.;Moorthi, S.;
      Pages: 3703 - 3711
      Abstract: A generalized multilevel inverter (MLI) with front-end dc–dc conversion stage followed by a synchronized H-bridge is presented. By using this configuration along with the proposed embedded control, any desired number of levels (n) in the output voltage can be produced. The dc–dc conversion stage employs an asynchronous buck converter. The duty cycle of dc–dc converter is varied in the form of m-level piecewise constant (PWC) unidirectional sine wave to produce a similar output voltage across the dc-link capacitor. The unidirectional PWC voltage is made into n-level ac voltage, where $n = (2m - 1)$ , by the synchronized H-bridge. Hence, it is named as dc–dc–ac MLI. An 8-bit Xilinx SPARTAN 3AN field programmable gate array (FPGA)-based digital controller is utilized for the simultaneous generation of high-frequency switching pulses for dc–dc converter and synchronized fundamental frequency switching pulses for H-bridge. The desired number of levels in ac output voltage and its frequency are the essential inputs to the pulse generation algorithm implemented in FPGA. The proposed MLI is simulated in MATLAB/Simulink environment; its functioning is verified with resistive (R) and resistive–inductive (R–L) loads. The hardware prototype of MLI is built in the laboratory and its performance is validated with R, R–L loads, and few home appliances.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Fully Integrated and Battery-Free Interface for Low-Voltage
           Electromagnetic Energy Harvesters
    • Authors: Ulusan; H.;Gharehbaghi, K.;Zorlu, O.;Muhtaroglu, A.;Kulah, H.;
      Pages: 3712 - 3719
      Abstract: This paper presents a fully integrated and battery-free 90 nm interface circuit for ac/dc conversion and step up of low-voltage ac signals generated by electromagnetic (EM) energy harvesters. The circuit is composed of two stages: The rectifier in the first stage utilizes an improved ac/dc doubler structure with active diodes internally powered by a passive ac/dc doubler and custom-designed comparators to minimize the voltage drops. With this, the efficiency is enhanced to 67% while providing 0.61 V to 40 μA load. The second stage is a dc/dc converter utilizing a low-voltage charge pump with an on-chip ring oscillator for further voltage step up. The rectifier stage is functional down to 125 mV input peak voltage, and the full interface circuit can maintain more than 1 V dc at 1 MΩ load for input peak voltages higher than 0.4 V. The circuit delivers 2.48 V to a 4.4 MΩ load, when interfaced to an in-house EM harvester, operating under 10 Hz, 0.5 g vibration.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A High-Efficiency Fast-Transient-Response Buck Converter with
           Analog-Voltage-Dynamic-Estimation Techniques
    • Authors: Hwang; Y.;Liu, A.;Chang, Y.;Chen, J.;
      Pages: 3720 - 3730
      Abstract: A fast-transient-response buck converter utilizing analog-voltage-dynamic-estimation (AVDE) techniques is proposed in this paper. The responses of the proposed buck converter are very fast when load changes between heavy load and light load. The switching frequency of the proposed buck converter is 1 MHz for nominal 3.3 V input and 1.0–2.5 V output range application. Experimental results prove that the proposed scheme improves the transient response to within 2 μs and that its maximum power efficiency can be up to 95%. The maximum load current is 300 mA. The proposed AVDE buck converter has been fabricated with a commercial 0.35 μm CMOS 2P4M process, the total chip area is about $1.5; {rm mm} times 1.5 ;{rm mm}$ , including PADs.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Cell-to-Cell Battery Equalizer With Zero-Current Switching and
           Zero-Voltage Gap Based on Quasi-Resonant LC Converter and
           Boost Converter
    • Authors: Shang; Y.;Zhang, C.;Cui, N.;Guerrero, J.M.;
      Pages: 3731 - 3747
      Abstract: In conventional equalizers, the facts of bulky size and high cost are widespread. Particularly, the zero-switching loss and zero-voltage gap (ZVG) between cells are difficult to implement due to the high-frequency hard switching and the voltage drop across power devices. To overcome these difficulties, a direct cell-to-cell battery equalizer based on quasi-resonant LC converter (QRLCC) and boost dc–dc converter (BDDC) is proposed. The QRLCC is employed to gain zero-current switching, leading to a reduction of power losses. The BDDC is employed to enhance the equalization voltage gap for large balancing current and ZVG between cells. Moreover, through controlling the duty cycle of the BDDC, the topology can online adaptively regulate the equalization current according to the voltage difference, which not only effectively prevents overequalization but also abridges the overall balancing time. Instead of a dedicated equalizer for each cell, only one balancing converter is employed and shared by all cells, reducing the size and implementation cost. Simulation and experimental results show the proposed scheme exhibits outstanding balancing performance, and the energy conversion efficiency is higher than 98%. The validity of the proposed equalizer is further verified by a quantitative and systematic comparison with the existing active balancing methods.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • ON/OFF Control of a Modular DC–DC Converter Based on Active-Clamp
           LLC Modules
    • Authors: Nguyen; H.;Zane, R.;Maksimovic, D.;
      Pages: 3748 - 3760
      Abstract: This paper studies ON/OFF control of a dc–dc system that contains multiple active-clamp LLC resonant modules operating in parallel. The architecture and the ON/OFF control method yield high overall efficiency and fast transient responses. Two converter models are introduced: 1) a high-frequency model to determine a gate timing sequence that enables fast ON/OFF control, and 2) an averaged model to assist in the system control loop design. The models and the ON/OFF control method are verified by experiments on a prototype consisting of two 1-MHz, 24–3.3-V, 5-W active-clamp LLC modules. The performance of PI and PID system controllers is compared, and capacitor size is analyzed by simulations on systems containing up to 20 modules.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Switching Control Strategy for Single- and Dual-Inductor Current-Fed
           Push–Pull Converters
    • Authors: Nayanasiri; D.R.;Foo, G.H.B.;Vilathgamuwa, D.M.;Maskell, D.L.;
      Pages: 3761 - 3771
      Abstract: A switching control strategy is proposed for single- and dual-inductor current-fed push–pull converters. The proposed switching control strategy can be used with both current-fed push–pull converters with an active voltage doubler rectifier, or active rectifier, in the secondary-side of the isolation transformer. The proposed switching control strategy makes turn-on and turn-off processes of the primary-side power switches zero-voltage switching and zero-current switching, respectively. The soft-switching operation of the single- and dual-inductor push–pull converters, with both types of active rectifier, is explained. Simulation and experimental results are provided to validate soft-switching operation of the current-fed push–pull converters with the proposed switching control strategy.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Single-Stage Solar-Powered LED Display Driver Using Power Channel Time
           Multiplexing Technique
    • Authors: Zhang; Y.;Ma, D.;
      Pages: 3772 - 3780
      Abstract: A unified single-stage solar harvester/LED display driver with power channel time multiplexing technique is proposed to achieve simultaneous maximum power point tracking (MPPT) and LED current regulation using two control variables. The operation state is automatically selected between power redundant and power hungry states to implement adaptive power steering. The D-hopping technique is proposed to ensure fast LED current recovery during PWM dimming and uninterruptible MPPT and LED powering. This design is fabricated with 0.25-μm CMOS process. The LED current is regulated between 20 and 50 mA with 500-kHz switching frequency. An 85-ns PWM dimming recovery time is achieved. No observable fluctuations are found during the PWM dimming and solar energy available/unavailable transitions.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Reversible Position Sensorless Controlled Switched-Reluctance Motor
           Drive With Adaptive and Intuitive Commutation Tunings
    • Authors: Hu; K.;Chen, Y.;Liaw, C.;
      Pages: 3781 - 3793
      Abstract: This paper presents a reversible position sensorless switched reluctance motor (SRM) drive with adaptive and intuitive commutation instant tunings. The narrow voltage pulses are injected into an unenergized phase winding via the PWM channel. The resulted amplitude modulated winding currents are sensed and signal processed to yield the observed Hall signal. No external injection circuit and the motor parameters are required. The estimated rotor speed is obtained from the observed Hall signal. The motor is first started in stepping motor mode, and then it is changed to the sensorless SRM mode as the speed is raised to a suited value. The smooth and fast starting as well as reversible operations are yielded. To improve the torque generating capability, an adaptive commutation tuning control scheme with the identified winding inductance is developed to set the commutation shift angle according to the observed speed, the winding current command, and observed inductance. Moreover, the static intuitive commutation tuning is further conducted in static period to pursuit maximum torque-per-ampere characteristics. Experimental evaluation shows that the developed position sensorless SRM drive possesses very smooth reversible operation and driving performance within a wide speed range, even higher than rated speed.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Direct Power Control of a Three-Phase Inverter for Grid Input Current
           Shaping of a Single-Phase Diode Rectifier With a Small DC-Link Capacitor
    • Authors: Son; Y.;Ha, J.;
      Pages: 3794 - 3803
      Abstract: This paper describes motor drive system fed by a single-phase diode rectifier without power factor correction (PFC) circuit or the input filter. The system considered in this paper consists of a single-phase diode rectifier, a three-phase inverter, and a small dc-link capacitor. Since dc-link capacitance of the proposed system is few microfarads, the shape of the grid input current is directly affected by electrical output power of the inverter. Using this aspect, two goals of the drive system, controlling torque of the motor and suppressing the grid input current harmonics, can be simultaneously achieved by controlling the output power of the inverter. The proposed method includes the motor current reference generation and the direct output power regulation by modifying the output voltage reference. With the proposed method, the harmonic components of the grid input current can be reduced under the limits of the regulation IEC61000-3-2, lower than those in the conventional method. Also, the cost and size of the inverter system can be significantly reduced by removing electrolytic dc-link capacitor and input filter from the system. The performance of the proposed shaping method was validated by the experimental results using the motor drive system with a 5μF film capacitor at dc link.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A 12-Sector Space Vector Switching Scheme for Performance Improvement of
           Matrix-Converter-Based DTC of IM Drive
    • Authors: Sebtahmadi; S.S.;Pirasteh, H.;Aghay Kaboli, S.H.;Radan, A.;Mekhilef, S.;
      Pages: 3804 - 3817
      Abstract: This paper presents a direct torque control (DTC) switching scheme based on the direct matrix converter (DMC) using a 12-side polygonal space vector for variable speed control of an induction motor (IM). The conventional DTC scheme-based matrix converter (MC) is limited by 60° sectors of both flux and voltage vectors, which introduce a high torque ripple. The proposed method utilizes twelve 30° sectors of both flux and voltage vectors to increase the degrees of freedom for selection of proper vectors and reduce the torque ripple. The proposed switching scheme for the MC-based DTC of an IM drive select the appropriate switching vectors for control of torque with small variations of the stator flux within the hysteresis band. This improves the degrees of freedom in selecting the vector algorithm and the torque ripple as well. Furthermore, during the large torque demand, the probabilities of transgressing reference vector limits, which are enclosed by 12-side polygonal space vector, are reduced. Extensive simulation and experimental results are presented to verify the effectiveness of the 12-sector space vector switching scheme for the DTC of an IM fed by the DMC.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Generalized Two-Vector-Based Model-Predictive Torque Control of Induction
           Motor Drives
    • Authors: Zhang; Y.;Yang, H.;
      Pages: 3818 - 3829
      Abstract: Conventional single-vector-based model-predictive torque control (MPTC) has been widely studied owing to its intuitive concept and quick response. To improve the steady-state performance, recently, the concept of duty cycle control was introduced in MPTC by inserting a null vector along with an active vector during one control period. However, this still fails to reduce the torque error to a minimal value due to the imposed restriction on vector combination and the cascaded processing of vector selection and vector duration. This paper proposes a generalized two-vectors-based MPTC (GTV-MPTC) by relaxing the vector combination to two arbitrary voltage vectors. By evaluating the vector combination and their durations simultaneously in the predefined cost function, global minimization of torque error can be obtained in theory. However, the computational burden is also significantly increased. By choosing a proper method to determine the vector durations, the redundant vector combinations can be eliminated, which makes the proposed GTV-MPTC suitable for real-time implementation. Both simulation and experimental results were carried out to verify the effectiveness of the proposed method. The presented results show that, compared to prior MPTC with or without duty cycle control, the proposed GTV-MPTC achieves much better performance with lower sampling frequency over a wide speed range. Furthermore, the average switching frequency is even lower than that of conventional MPTC in the medium speed range.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Power Flow Analysis and Critical Design Issues of Retrofit Light-Emitting
           Diode (LED) Light Bulb
    • Authors: Li; S.;Chen, H.;Tan, S.;Hui, S.Y.R.;Waffenschmidt, E.;
      Pages: 3830 - 3840
      Abstract: For retrofit applications, some high-brightness light-emitting diode (LED) products have the same form factor restrictions as existing incandescent light bulbs. Such form factor constraints may restrict the design and optimal performance of the LED technology. In this paper, some critical design issues for commercial LED bulbs designed for replacing E27 incandescent lamps are quantitatively analyzed. The analysis involves power audits on such densely packed LED systems so that the amounts of power consumption in: 1) the LED wafer; 2) the phosphor coating; and 3) the lamp translucent cover are quantified. The outcomes of such audits enable R&D engineers to identify the critical areas that need further improvements in a compact LED bulb design. The strong dependence of the luminous output of the compact LED bulb on ambient temperature is also highlighted.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Static and Dynamic Photoelectrothermal Modeling of LED Lamps Including
           Low-Frequency Current Ripple Effects
    • Authors: Almeida; P.S.;Bender, V.C.;Braga, H.A.C.;Dalla Costa, M.A.;Marchesan, T.B.;Alonso, J.M.;
      Pages: 3841 - 3851
      Abstract: In this paper, a static and dynamic photoelectrothermal model including the impact of low-frequency current ripple on light-emitting diodes (LEDs) performance is proposed. The objective of this study is to evaluate the dynamical interaction among thermal, photometrical, and electrical properties of the LEDs when they are supplied by a dc constant current with a superposed low frequency sinusoidal ripple, which is the common case in offline LED drivers. Therefore, this paper presents both a model and experimental data for analyzing the LED photometrical behavior in terms of luminous flux, efficacy, flicker, and chromaticity. Three laboratory prototypes with different heat sinks and LED models have been tested. Experimental results are presented to evaluate the LED photometrical behavior under the aforementioned operating conditions and to validate the proposed modeling methodology.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Proportional-Integral (PI) Compensator Design of Duty-Cycle-Controlled
           Buck LED Driver
    • Authors: Kim; M.;
      Pages: 3852 - 3859
      Abstract: A discrete time-domain modeling and design for the duty-cycle-controlled buck light-emitting diode (LED) driver is presented in this paper. The discrete time-domain equation representing the buck LED driver is derived and linearized about the equilibrium state. Also the switching control law, the proportional-integral (PI) compensator is used here as an example of the error amplifier, is linearized about the equilibrium state. The linearized buck LED driver and the control law are then combined to arrive at a linearized duty-cycle-controlled buck LED driver. The root-locus method is employed to analyze the dynamic performance of the closed-loop system. Based on the modeling result, a practical design equation for the PI compensator is derived. Experimental results are presented to verify the validity of the proposed PI compensator design.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Capacitor-Isolated Multistring LED Driver With Daisy-Chained Transformers
    • Authors: Zhang; R.;Chung, H.S.;
      Pages: 3860 - 3875
      Abstract: By extending a prior-art transformer-isolated structure for driving multiple LED strings, a scalable and modular capacitor-isolated architecture is presented in this paper. The proposed idea is based on first utilizing a daisy-chained transformer structure to share equally the current delivered from a half-bridge switching circuit and supply the shared currents to multiple string networks and then using a capacitor network in each string network to derive the string current and separate the grounds of the input source and the strings. The capacitor networks give further advantage of balancing the string currents, as compared to the prior-art transformer-isolated structure. Dimming function is achieved by adjusting both the switching frequency and duty cycle of the switching devices in the switching circuit. A 21-W prototype with seven strings has been built and evaluated. The lamp can be dimmed to 10% of full output, and the LED string current can be regulated at less than ±1% error, even under significant variations in the string voltages and some LED failures.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Thermal Analysis of LED Lamps for Optimal Driver Integration
    • Authors: Perpina; X.;Werkhoven, R.J.;Vellvehi, M.;Jakovenko, J.;Jorda, X.;Kunen, J.M.G.;Bancken, P.;Bolt, P.J.;
      Pages: 3876 - 3891
      Abstract: This paper studies the thermal influence of a light-emitting diode (LED) driver on a retrofit LED lamp, also reporting on a procedure for its thermal characterization and multiscale modeling. In this analysis, temperature is measured by infrared thermography and monitoring specific locations with thermocouples. Experimental results point out that temperature increases considerably in all lamp parts when the driver is installed in the lamp (up to 15% for LED board). The multiscale simulation approach is set with thermal parameters (thermal conductivity, emissivity, and LED board thermal resistance) measured from several parts of the lamp, reaching an agreement between experiment and simulation smaller than 10%. With this model, the driver temperature is investigated under operational conditions accounting for two alternative thermal designs. First, the driver is completely surrounded with a filling material (air completely removed, Case A), and, second, only the thermal contact between the board and the lamp is improved (air is kept, Case B). In both cases, the heat removal from the driver to the ambient by conduction is enhanced, observing that temperature decreases in its most heated components up to 10 °C in Case A, and up to 7 °C in Case B.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Dead-Time Compensation Method for Parabolic Current Control With
           Improved Current Tracking and Enhanced Stability Range
    • Authors: Zhang; L.;Gu, B.;Dominic, J.;Chen, B.;Zheng, C.;Lai, J.;
      Pages: 3892 - 3902
      Abstract: Hysteresis current control is an attractive nonlinear current-control method for voltage source inverters when a fast system response is required. A well-known disadvantage of hysteresis current control is that the system has to operate over a wide switching frequency range. This causes an increase in the switching losses of the system and increases the difficulty in designing the output filter. The recently proposed parabolic current control solves this problem by employing a pair of parabolic carriers as the control band. Through the use of parabolic current control, constant switching frequency can be achieved. In the implementation of parabolic current control, dead time is employed to prevent shoot through of the inverter leg. The employment of dead time impacts the current-tracking precision and the stability range of the parabolic current-control method. Another side effect of using dead time is that the switching frequency deviates from the desired value. In this paper, the effects of dead time on parabolic current control are analyzed, and a compensation method is proposed for voltage source inverters that use parabolic current control. Using the output current direction of the voltage source inverter, a new pair of improved parabolic carriers is derived. As a result, the current error can be well controlled and the effects of dead time can be eliminated. The improvement in the current tracking of the system comes with an added benefit where the duty cycle range is extended. The effectiveness of the proposed dead-time compensation method is experimentally verified by the use of a full-bridge voltage source inverter.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Extended Application of D- ${bf
    Digital Control to a Single-Phase
           Bidirectional Inverter With an LCL Filter
    • Authors: Wu; T.;Lin, L.;Yao, N.;Chen, Y.;Chang, Y.;
      Pages: 3903 - 3911
      Abstract: Division-summation (D-Σ) digital control has been successfully applied to the single-phase bidirectional inverter with an LC filter, which can cover wide inductance variation and achieve precise inverter current tracking. However, high frequency ripple current injection to the grid cannot be avoided, and an LCL filter is therefore required. Since there typically exist grid voltage harmonics, the injected grid current will contain harmonic components due to the effect of the LCL-filter capacitor. This paper presents an extended application of the D-Σ digital control associated with a filter-capacitor-current compensation to reduce the injected grid-current harmonics. The control laws of the inverter with the D-Σ digital control and compensation approach are derived in detail, and the reduction of grid-current harmonics is analyzed. With the proposed approaches, the phase margin between the output impedance of the inverter and grid impedance can be higher than 80° from low to high frequencies, and the inverter can achieve high harmonic voltage rejection ratio up to 39th harmonic, which is relatively suitable for weak grid connection. Experimental results measured from a 5-kW single-phase bidirectional inverter have verified the feasible application of the D-Σ digital control and proposed compensation.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Frequency Adaptive Selective Harmonic Control for Grid-Connected Inverters
    • Authors: Yang; Y.;Zhou, K.;Wang, H.;Blaabjerg, F.;Wang, D.;Zhang, B.;
      Pages: 3912 - 3924
      Abstract: In this paper, a frequency adaptive selective harmonic control (FA-SHC) scheme is proposed. The FA-SHC method is developed from a hybrid SHC scheme based on the internal model principle, which can be designed for grid-connected inverters to optimally mitigate feed-in current harmonics. The hybrid SHC scheme consists of multiple parallel recursive ( $nkpm m$ )-order ( $k$ = 0, 1, 2, $ldots$ , and $mle n/2$ ) harmonic control modules with independent control gains, which can be optimally weighted in accordance with the harmonic distribution. The hybrid SHC, thus, offers an optimal tradeoff among cost, complexity, and also performance in terms of high accuracy, fast response, easy implementation, and compatible design. The analysis and synthesis of the hybrid SHC are addressed. More important, in order to deal with the harmonics in the presence of grid frequency variations, the hybrid SHC is transformed into the FA-SHC, being the proposed fractional-order controller, when it is implemented with a fixed sampling rate. The FA-SHC is implemented by substituting the fractional-order elements with the Lagrange-polynomial-based interpolation filters. The proposed FA-SHC scheme provides fast on-line computation and frequency adaptability to compensate harmonics in grid-connected applications, where the grid frequency is usually varying within a certain range (e.g., 50 $pm$ 0.5 Hz). Experimental tests have demonstrated the effectiveness of the proposed FA-SHC scheme in terms of accurate frequency adaptability and also fast transient response.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Automatic Resonant Frequency Tracking in Parallel LLC Boost DC–DC
    • Authors: Kundu; U.;Chakraborty, S.;Sensarma, P.;
      Pages: 3925 - 3933
      Abstract: This paper proposes an automatic resonant frequency tracking scheme for resonant converters. A plant modeling approach is presented based on realistic ramp variation of resonant frequency due to slowly varying environmental conditions. The drift in resonant frequency is detected by observing the phase relationship of an electrical variable pair. A rigorous analysis is carried out to select the most suitable variable pair for phase comparison. The effects of circuit nonidealities on the proposed phase detection technique have been detailed. The proposed control technique has been implemented using low cost analog circuitry and is applied to a parallel LLC tank-based resonant boost dc–dc converter. Experimental results are presented on a 160-W prototype to validate the analytical predictions.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • An Estimator-Based Distributed Voltage-Predictive Control Strategy for AC
           Islanded Microgrids
    • Authors: Wang; Y.;Chen, Z.;Wang, X.;Tian, Y.;Tan, Y.;Yang, C.;
      Pages: 3934 - 3951
      Abstract: This paper presents an estimator-based voltage-predictive control strategy for ac islanded microgrids, which is able to perform voltage control without any communication facilities. The proposed control strategy is composed of a network voltage estimator and a voltage-predictive controller for each distributed generator, where the voltage estimator serves as an essential tool to obtain network voltages response without using communication links, while the voltage-predictive controller is able to implement offset-free voltage control for a specified bus. The dynamic performance of the proposed voltage control strategy is analyzed through small-signal analysis method, from which the design guideline for the controller parameters is formulated. Furthermore, the robustness of the proposed voltage control strategy is investigated under a series of parameters uncertainties, including the line parameters perturbation, load parameters variation, different disturbance locations, LC filters perturbation, output impedances perturbation, and DG unit fault. The simulation and experimental results show that the proposed control approach is able to perform offset-free voltage control without any communication links and has a good capability to reject uncertain perturbations of islanded microgrids.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Analysis and Tracking of Optimal Load in Wireless Power Transfer Systems
    • Authors: Fu; M.;Yin, H.;Zhu, X.;Ma, C.;
      Pages: 3952 - 3963
      Abstract: All the wireless power transfer (WPT) systems share a similar configuration including a power source, a coupling system, a rectifying circuit, a power regulating, and charging management circuit and a load. For such a system, both a circuit- and a system-level analyses are important to derive requirements for a high overall system efficiency. Besides, unavoidable uncertainties in a real WPT system require a feedback mechanism to improve the robustness of the performance. Based on the above basic considerations, this paper first provides a detailed analysis on the efficiency of a WPT system at both circuit and system levels. Under a specific mutual inductance between the emitting and receiving coils, an optimal load resistance is shown to exist for a maximum overall system efficiency. Then, a perturbation-and-observation-based tracking system is developed through additional hardware such as a cascaded boost-buck dc–dc converter, an efficiency sensing system, and a controller. Finally, a 13.56-MHz WPT system is demonstrated experimentally to validate the efficiency analysis and the tracking of the optimal load resistances. At a power level of 40 W, the overall efficiency from the power source to the final load is maintained about 70% under various load resistances and relative positions of coils.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • An Immune-Algorithm-Based Dead-Time Elimination PWM Control Strategy in a
           Single-Phase Inverter
    • Authors: Yuan; J.;Zhao, Z.;Chen, B.;Li, C.;Wang, J.;Tian, C.;Chen, Y.;
      Pages: 3964 - 3975
      Abstract: In this paper, an immune algorithm (IA)-based dead-time elimination PWM control strategy is proposed. For existing dead-time elimination applications, one of the major problems is the dead-time control around the zero-current-crossing points. To deal with this problem, this paper proposes a different PWM control method which first restricts the control sequence to a specified level around the zero-crossing zone. Also, the proposed method can improve the current waveform quality by using the IA approach and three-level control strategy. Compared with conventional dead-time elimination methods, this technique has the features of simple hardware requirement and adaptive control. Moreover, this control strategy effectively eliminates the effect of dead-time, while at the same time significantly reducing the total harmonic distortion of output current and improving the amplitude of output RMS value in different modulation indexes and loads conditions. To verify the analysis, an experimental platform based on DSP and field-programmable gate array is built. The simulation and experimental results are given to demonstrate the effectiveness and feasibility of this new method.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • An Extended Lyapunov-Function-Based Control Strategy for Single-Phase UPS
    • Authors: Komurcugil; H.;Altin, N.;Ozdemir, S.;Sefa, I.;
      Pages: 3976 - 3983
      Abstract: In this study, an extended Lyapunov-function-based control strategy that assures global asymptotic stability is proposed for single-phase UPS inverters. The Lyapunov function is formed from the energy stored in the inductor and capacitor due to the fact that the system states converge to the equilibrium point if the total energy is continuously dissipated. It is shown analytically that the classical Lyapunov-function-based control leads to a globally asymptotically stable system at the expense of steady-state errors in the output voltage, which exist due to the lack of outer voltage loop in the control input. Therefore, an extended Lyapunov-function-based control strategy is proposed, which eliminates the steady-state error without destroying the global stability of the closed-loop system. The steady state and dynamic performance of the proposed control strategy has been tested by simulations and experiments under resistive and diode bridge rectifier loads. The results obtained from a 1-kW inverter demonstrate that the developed control strategy not only offers global stability, but also leads to good quality sinusoidal voltage with a reasonably low THD, almost zero steady-state error in the output voltage, and fast dynamic response under linear and nonlinear loads.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Minimization of the DC Component in Transformerless Three-Phase
           Grid-Connected Photovoltaic Inverters
    • Authors: Yan; Q.;Wu, X.;Yuan, X.;Geng, Y.;Zhang, Q.;
      Pages: 3984 - 3997
      Abstract: The dc component is a special issue in transformerless grid-connected photovoltaic (PV) inverter systems and may cause problems regarding system operation and safety. IEEE standard 1547-2003 has defined the limit for dc component in the grid-side ac currents, e.g., below 0.5% of the rated current. The dc component can cause line-frequency power ripple, dc-link voltage ripple, and a further second-order harmonic in the ac current. This paper has proposed an effective solution to minimize the dc component in three-phase ac currents and developed a software-based approach to mimic the blocking capacitors used for the dc component minimization, the so-called virtual capacitor. The “virtual capacitor” is achieved by adding an integral of the dc component in the current feedback path. A method for accurate extraction of the dc component based on double time integral, as a key to achieve the control, has been devised and approved effective even under grid-frequency variation and harmonic conditions. A proportional-integral-resonant controller is further designed to regulate the dc and line-frequency component in the current loop to provide precise control of the dc current. The proposed method has been validated on a 10-kVA experimental prototype, where the dc current has been effectively attenuated to be within 0.5% of the rated current. The total harmonic distortion and the second-order harmonic have also been reduced as well as the dc-link voltage ripple.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • A Maximum Efficiency Point Tracking Control Scheme for Wireless Power
           Transfer Systems Using Magnetic Resonant Coupling
    • Authors: Li; H.;Li, J.;Wang, K.;Chen, W.;Yang, X.;
      Pages: 3998 - 4008
      Abstract: With a good balance between power transfer distance and efficiency, wireless power transfer (WPT) using magnetic resonant coupling is preferred in many applications. Generally, WPT systems are desired to provide constant output voltage with the highest possible efficiency as power supplies. However, the highest efficiency is not achieved by the reported closed-loop WPT systems that maintain constant output voltage against coupling and load variations. In this paper, an efficiency evaluation method is put forward to evaluate the closed-loop control schemes. Furthermore, a maximum efficiency point tracking control scheme is proposed to maximize the system efficiency while regulating the output voltage. This control scheme is unique and prominent in that it fixes the operating frequency at the receiving-side resonant frequency and converts both the input voltage and the load resistance at the same time. Thus, the maximum efficiency point on the constant output voltage trajectory can be tracked dynamically. Therefore the system's output voltage can be maintained constant and its efficiency is always the highest. The experimental results show that the maximum efficiency point is tracked and a very high overall efficiency is achieved over wide ranges of coupling coefficient and load resistance.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Analysis of Critical Inductance and Capacitor Voltage Ripple for a
           Bidirectional Z -Source Inverter
    • Authors: Dong; S.;Zhang, Q.;Cheng, S.;
      Pages: 4009 - 4015
      Abstract: An analysis of the critical inductance and capacitor voltage ripple of bidirectional Z-source was presented in this paper. Varying inductances were found to lead to different operational modes of the inverter. The critical inductance was derived. While the Z-source capacitor voltage ripple is traditionally considered to be independent of the inductance with large inductance, it was found that dependence exists when small inductors are used. The capacitor voltage ripple was also derived. These theoretical findings have been verified using both simulations and experimental results.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Dead-Time Compensation Method Based on Current Ripple Estimation
    • Authors: Mannen; T.;Fujita, H.;
      Pages: 4016 - 4024
      Abstract: This paper discusses the voltage error caused by the dead time in voltage-source PWM converters. The theoretical analysis in this paper derives the nonlinear voltage error paying attention to the parasitic output capacitance in each switching device. The analytical result reveals that the turn-off current or the switching current ripple strongly affects the voltage error. In addition, it is clarified that the conventional compensation methods based on linear and three-level approximation are suitable under small and large current ripple conditions, respectively. A simple calculation method of current ripples in three-phase PWM converters is also developed to estimate the turn-off currents. Turn-off transition compensation method which is a new compensation method based on the analysis is developed and compared with three different conventional methods in experiments using a 200-V, 5-kW three-phase grid-connection converter. The proposed method exhibits a good compensation performance having a lower voltage THD than the conventional methods in all over the operating range.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • Maximum Energy Efficiency Tracking for Wireless Power Transfer Systems
    • Authors: Zhong; W.X.;Hui, S.Y.R.;
      Pages: 4025 - 4034
      Abstract: A method for automatic “maximum energy efficiency tracking” operation for wireless power transfer (WPT) systems is presented in this paper. Using the switched-mode converter in the receiver module to emulate the optimal load value, the proposed method follows the maximum energy efficiency operating points of a WPT system by searching for the minimum input power operating point for a given output power. Because the searching process is carried out on the transmitter side, the proposal does not require any wireless communication feedback from the receiver side. The control scheme has been successfully demonstrated in a two-coil system under both weak and strong magnetic coupling conditions. Experimental results are included to confirm its feasibility.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
  • ${bf{rm+I}^2}$+ +Controlled+Buck+Converters+in+CCM&rft.title=IEEE+Transactions+on+Power+Electronics&rft.issn=0885-8993&;">Prediction of Subharmonic Oscillation in        notation="LaTeX">${bf{rm I}^2}$ Controlled
           Buck Converters in CCM
    • Authors: Fang; C.;
      Pages: 4035 - 4036
      Abstract: A recent paper proposed $rm{I}^2$ average-current control with constant switching period (CSP) or constant on-time (COT) operation in continuous conduction mode (CCM). The small-signal analysis was presented, but only for the COT case. No instability or its condition was reported. In this note, unified subharmonic oscillation conditions are derived for both CSP and COT buck converters. The effects of feedback gain, turn-off delay, and stabilizing ramp slope are considered. The results can be extended to other converters or control schemes.
      PubDate: July 2015
      Issue No: Vol. 30, No. 7 (2015)
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