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Frontiers in Energy

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ISSN (Print) 2095-1701 - ISSN (Online) 2095-1698
Published by Springer-Verlag

[2216 journals]

A review of recent experimental investigations and theoretical analyses for pulsating heat pipes
- Abstract: Abstract Pulsating heat pipe (PHP), or oscillating heat pipe (OHP), a novel type of highly efficient heat transfer component, has been widely applied in many fields, such as in space-borne two-phase thermal control systems, in the cooling of electronic devices and in energy-saving technology, etc. In the present paper, the characteristics and working principles of the PHPs are introduced and the current researches in the field are described from the viewpoint of experimental tests, theoretical analyses as well as practical applications. Besides, it is found that the state-of-the-art experimental investigations on the PHPs are mainly focused on the flow visualization and the applications of nanofluids and other functional fluids, aiming at enhancing the heat transfer performance of the PHPs. In addition, it is also pointed out that the present theoretical analyses of the PHP are restricted by further development of two-phase flow theories, and are concentrated in the non-linear analyses. Numerical simulations are expected to be another research focus, in particular of the combination of the nanofluids and functional fluids.
  PubDate: 2013-05-16
Dynamic characteristics and improved MPPT control of PV generator
- Abstract: Abstract This paper presents a mathematical model of photovoltaic (PV) module and gives a strategy to calculate online the maximum power point (MPP). The variation of series and shunt resistor are taken into account in the model and are dynamically identified using the Newton-Raphson algorithm. The effectiveness of the proposed model is verified by laboratory experiments obtained by implementing the model on the dSPACE DS1104 board.
  PubDate: 2013-05-16
Optimal placement of PMUs for the smart grid implementation in Indian power grid—A case study
- Abstract: Abstract Efficient utilization of energy resources is essential for a developing country like India. The concept of smart grid (SG) can provide a highly reliable power system with optimized utilization of available resources. The present Indian power grid requires revolutionary changes to meet the growing demands and to make the grid smarter and reliable. One of the important requirements for SG is the instantaneous monitoring of the voltage, current and power flows at all buses in the grid. The traditional monitoring system cannot satisfy this requirement since they are based on nonlinear power flow equations. Synchro-phasor-measurement devices like phasor measurement units (PMUs) can measure the phasor values of voltages at installed buses. Consequently, the currents passing through all branches connected to that bus can be computed. Since the voltage phasor values at the neighboring buses of a bus containing the PMU can be estimated using Ohm’s law, it is redundant to install PMUs at all the buses in a power grid for its complete observability. This paper proposes the optimal geographical locations for the PMUs in southern region Indian power grid for the implementation of SG, using Integer Linear Programming. The proposed optimal geographical locations for PMU placement can be a stepping stone for the implementation of SG in India.
  PubDate: 2013-05-11
Robust control based on the Lyapunov theory of a grid-connected doubly fed induction generator
- Abstract: Abstract This paper discusses the robust control of a grid-connected doubly-fed induction generator (DFIG) controlled by vector control using a nonlinear feedback linearization strategy in order to ameliorate the performances of the control and to govern the developed stator active and reactive power in a linear and decoupled manner, in which an optimal operation of the DFIG in subsynchronous operation is given, as well as the control stator power flow with the possibility of keeping stator power factor at a unity. The use of the state-all-flux induction machine model gives place to a simpler control model. So, to achieve this objective, the Lyapunov approach is used associated with a sliding mode control to guarantee the global asymptotical stability and the robustness of the parametric variations.
  PubDate: 2013-05-11
Comparison of optimal capacitor placement methods in radial distribution system with load growth and ZIP load model
- Abstract: Abstract In this paper, a combined power loss sensitivity (PLS) index-based approach is proposed to determine the optimal location of the capacitors in the radial distribution system (RDS) based on the real and reactive combined loss sensitivity index, as capacitor placement not only reduces real power loss with voltage profile improvement but also reduces reactive power loss due to the reactive power compensation in the network. The results have been obtained with the existing methods of power loss index (PLI) and index vector (IV) method for comparison. Besides, the optimal placement has been obtained with the proposed method as well as existing methods and the total kVar support has been obtained. In addition, the results of net cost savings for the 10-, 34-, and 69-bus systems are obtained for comparison. Moreover, the results have been obtained for a large system of 85 buses to validate the results with combined sensitivity based approach. Furthermore, the load growth factor has been considered in the study which is essential for the planning and expansion of the existing systems, whereas the impact of the realistic load model as ZIP load model has been considered for the study of all the systems.
  PubDate: 2013-05-11
Integrated transmission and generation planning model in a deregulated environment
- Abstract: Abstract After the deregulation of the Power Sector in the U.S., planning for generation and transmission capacities is decentralized. There is, however, still need for the long term integrated planning of generation and transmission capacities at the macro level, since these two sectors must operate in a coordinated manner. This paper presents a model for integrating generation and transmission expansion planning to identify an indicative expansion plan for the total sector at the macro level. The argument for an integrated model is supported using evidence from integrated planning efforts in real life systems. The application of the proposed model is illustrated using an example that requires expansion of generation and transmission capacities over three regions in a deregulated power system. The example considers that addition of generating capacity should come from renewable sources. The test results show the potential cost saving from integrated planning.
  PubDate: 2013-05-05
Experimental evaluation of a 35 kVA downdraft gasifier
- Abstract: Abstract Energy conversion systems based on biomass are particularly interesting because biomass utilization effectively closes the carbon cycle besides achieving self-sustainability. Biomass is particularly useful for highly populated and agriculture dependent economic nations like China and India. A compact and cost effective downdraft gasification system was developed. The present paper describes an experimental investigation on a biomass based gasifier engine system with a capacity of 35 kVA for power generation application. The problem of cooling and cleaning the hot and dirty gas from the gasifier has been satisfactorily solved by the effective cooling and filtration system. The gasifier developed is observed to be operation friendly. The quality of gas was evaluated in terms of its composition, conversion efficiency and total particulate matter. The maximum output of the power plant was obtained at the combustion zone temperature of 850°C. The experimental investigations showed that the percentage reduction in total particulate matter is 89.32%. The conversion efficiency of the biomass gasifier is found to be dependent on the operation conditions and fuel properties of the gasifier. The optimum value of equivalence ratio was observed to be 0.3134 for achieving the maximum gas conversion efficiency of the present gasifier configuration.
  PubDate: 2013-05-03
Combined heat and power economic dispatch problem using firefly algorithm
- Abstract: Abstract Cogeneration units, which produce both heat and electric power, are found in many process industries. These industries also consume heat directly in addition to electricity. The cogeneration units operate only within a feasible zone. Each point within the feasible zone consists of a specific value of heat and electric power. These units are used along with other units, which produce either heat or power exclusively. Hence, the economic dispatch problem for these plants to optimize the fuel cost is quite complex and several classical and meta-heuristic algorithms have been proposed earlier. This paper applies the firefly algorithm, which is inspired by the behavior of fireflies which attract each other based on their luminosity. The results obtained have been compared with those obtained by other methods earlier and showed a marked improvement over the earlier methods.
  PubDate: 2013-05-03
Transient emission simulation and optimization of turbocharged diesel engine
- Abstract: Abstract In order to alleviate the pressure of experimental research of turbocharged diesel engine under transient operations, a whole process simulation platform for turbocharged diesel engine under transient operations was established based on the multi-software coupling technologies of Matlab/Simulink, GT-Power, STAR-CD and artificial neural network. Aimed at the contradiction of NO x and soot emission control with exhaust gas recirculation (EGR) of turbocharged diesel engine under transient operations, on this simulation platform, a transient EGR valve control strategy was proposed, which adjusted the EGR valve in adjacent level based on the feedback of its opening according soot control limit under transient operations. Simulation and experimental results prove that the transient emission optimization effect of this control strategy is obvious. On the one hand, compared with the previous control strategy, which closed the EGR valve during the whole transient operations, soot emission is slightly increased by 9.5%, but it is still 9% lower than the control limit. On the other hand, compared with the previous control strategy, NO x transient emission is reduced by 44%.
  PubDate: 2013-04-29
Simulation of grid connection and maximum power point tracking control of brushless doubly-fed generator in wind power system
- Abstract: Abstract In this paper, based on the analysis of the mathematical model in a common synchronous reference frame of the brushless doubly-fed generator (BDFG), the grid connection strategy and maximum energy extraction control were both analyzed. Besides, the transient simulation of no-load model and generation model of the BDFG have been developed on the MATLAB/Simulink platform. The test results during cutting-in grid confirmed the good dynamic performance of grid synchronization and effective power control approach for the BDFG-based variable speed wind turbines.
  PubDate: 2013-04-29
Numerical simulation of combustion characteristics at different coal concentrations in bituminous coal ignition in a tiny-oil ignition burner
- Abstract: Abstract With the objective of producing a full-scale tiny-oil ignition burner, identical to the burner used in an 800 MWe utility boiler, numerical simulations were performed using Fluent 6.3.26 to study the progress of ignition for four coal concentration settings covering sub-operation conditions prevailing during the experiments performed with the burner. The numerical simulations conformed to the experimental results, demonstrating the suitability of the model used in the calculations. Simulations for a coal concentration of 0.40 kg/kg corresponding to a single burner operating at its rated output were also conducted, which indicated that gas temperatures along the burner centerline were high. As gas flowed to the burner nozzle, the high-temperature region expanded, ensuring a successful pulverized-coal ignition. With increasing coal concentration (0.08–0.40 kg/kg), the gas temperature along the burner centerline and at the first and second combustion chamber exits decreased at the equivalent radial points. At the center of the second combustion chamber exit, the O2 concentrations were almost depleted for the five coal concentrations, while the CO concentrations peaked.
  PubDate: 2013-04-29
A modified zone model for estimating equivalent room thermal capacity
- Abstract: Abstract The zone model has been widely applied in control analysis of heating, ventilation and air conditioning (HVAC) systems to achieve a high building efficiency. This paper proposed a modified zone model which is much simpler in the HVAC system simulation and has the similar accuracy to the complicated simulation model. The proposed model took into consideration the effect of envelop heat reservoir on the room indoor temperature by introducing the thermal admittance of the inner surfaces of the building enclosure. The thermal admittance for the building enclosure was developed based on the building thermal network analytical theory and transfer function method. The efficacy of the proposed model was demonstrated by comparing it with the complicated model — heat balance method (HTB2 program). The predicted results from the proposed model well agreed with those from the complicated simulation. The proposed model can then make the HVAC system dynamic simulation much faster and more acceptable for control design due to its simplicity and efficiency.
  PubDate: 2013-04-24
Constriction factor based particle swarm optimization for analyzing tuned reactive power dispatch
- Abstract: Abstract The reactive power dispatch (RPD) problem is a very critical optimization problem of power system which minimizes the real power loss of the transmission system. While solving the said problem, generator bus voltages and transformer tap settings are kept within a stable operating limit. In connection with the RPD problem, solving reactive power is compensated by incorporating shunt capacitors. The particle swarm optimization (PSO) technique is a swarm intelligence based fast working optimization method which is chosen in this paper as an optimization tool. Additionally, the constriction factor is included with the conventional PSO technique to accelerate the convergence property of the applied optimization tool. In this paper, the RPD problem is solved in the case of the two higher bus systems, i.e., the IEEE 57-bus system and the IEEE 118-bus system. Furthermore, the result of the present paper is compared with a few optimization technique based results to substantiate the effectiveness of the proposed study.
  PubDate: 2013-04-24
Experimental investigation and feasibility analysis of a thermophotovoltaic cogeneration system in high-temperature production processes
- Abstract: Abstract The experimental I–V characteristics of a Si cell module in a thermophotovoltaic (TPV) system were investigated using SiC or Yb2O3 radiator. The results demonstrate that the short-circuit current increases while the open-circuit voltage, along with the fill factor, decreases with the cell temperature when the radiator temperature increases from 1273 to 1573 K, leading to a suppressed increase of the output power of the system. The maximum output power density of the cell module is 0.05 W/cm2 when the temperature of the SiC radiator is 1573 K, while the electrical efficiency of the system is only 0.22%. The efficiency is 1.3% with a Yb2O3 radiator at the same temperature, however, the maximum output power density drops to 0.03 W/cm2. The values of the open-circuit voltage and the maximum output power obtained from the theoretical model conform to the experimental ones. But the theoretical short-circuit current is higher because of the existence of the contact resistance inside the cell module. In addition, the performance and cost of TPV cogeneration systems with the SiC or Yb2O3 radiator using industrial high-temperature waste heat were analyzed. The system electrical efficiency could reach 3.1% with a Yb2O3 radiator at 1573 K. The system cost and investment recovery period are 6732 EUR/kWel and 14 years, respectively.
  PubDate: 2013-04-21
Toward a nonlinear control of an AC-DC-PWM converter dedicated to induction heating
- Abstract: Abstract In this paper, a nonlinear control strategy applied to an AC-DC-pulse width modulation (PWM) converter is developed and simulated. First a nonlinear system modeling is derived with state variables of the input current and the output voltage by using power balance of the input and output. The system is linearized and decoupled, and then a state feedback law is obtained. For robust control of parameter perturbation, integrators are added to the exact feedback control law. The simulation is provided to verify the validity of the control algorithm.
  PubDate: 2013-04-21
Correlations for estimating solar radiation using sunshine hours and temperature measurement in Osogbo, Osun State, Nigeria
- Abstract: Abstract In this study, the global solar radiation on horizontal surface in Osogbo, Osun state, Nigeria was analyzed using 11-year data (1997–2007). Correlations using linear and quadratic expressions were developed to relate the global solar radiation on horizontal surface based on relative sunshine hours and temperature measurements for evaluating the monthly average daily global solar radiation. The calculated monthly clearness index values indicate that the prevailing weather condition in Osogbo is heavily overcast. All the developed quadratic correlations gave better correlation coefficients (0.834, 0.872 and 0.823 respectively) than the linear models. However, the Hargreaves and Samani related based quadratic model gave the best among the three developed quadratic expressions and is therefore suggested for estimating the monthly global radiation in this site and its surroundings.
  PubDate: 2013-04-18
Indoor thermal comfort research on the hybrid system of radiant cooling and dedicated outdoor air system
- Abstract: Abstract The radiant cooling system generally operates with the dedicated outdoor air system (DOAS). Air supply modes and the corresponding setting parameters of the hybrid system may substantially influence the indoor thermal comfort. With target indexes of air diffusion performance index (ADPI) and predicted mean vote (PMV), the Taguchi method was used to choose the optimal air supply mode and to analyze the significance of different factors on the thermal comfort. The results are expected for conducting the future design and regulation of the hybrid system. Computation fluid dynamics (CFD) simulation as well as verified experiments was performed during the research. Based on the ADPI studies, it is found that the air supply mode of ceiling delivery with ceiling exhaust is an optimized option to apply in DOAS of the hybrid system. Variance analysis results show that influence fact of air supply temperature is the most dominant one to impact the indoor thermal comfort index of PMV.
  PubDate: 2013-04-12
A solution to the unit commitment problem—a review
- Abstract: Abstract Unit commitment (UC) is an optimization problem used to determine the operation schedule of the generating units at every hour interval with varying loads under different constraints and environments. Many algorithms have been invented in the past five decades for optimization of the UC problem, but still researchers are working in this field to find new hybrid algorithms to make the problem more realistic. The importance of UC is increasing with the constantly varying demands. Therefore, there is an urgent need in the power sector to keep track of the latest methodologies to further optimize the working criterions of the generating units. This paper focuses on providing a clear review of the latest techniques employed in optimizing UC problems for both stochastic and deterministic loads, which has been acquired from many peer reviewed published papers. It has been divided into many sections which include various constraints based on profit, security, emission and time. It emphasizes not only on deregulated and regulated environments but also on renewable energy and distributed generating systems. In terms of contributions, the detailed analysis of all the UC algorithms has been discussed for the benefit of new researchers interested in working in this field.
  PubDate: 2013-04-02
Performance prediction of switched reluctance generator with time average and small signal models
- Abstract: Abstract This paper presents the complete mathematical model and predicts the performance of switched reluctance generator with time average and small signal models. The complete mathematical model is developed in three stages. First, a switching model is developed based on quasi-linear inductance profile. Next, based on the switching behaviour, a time average model is obtained to measure the difference between the excitation and generation time in each switching cycle. Finally, to track control voltage and current wave shapes, a small signal model is designed. The effectiveness of the complete multilevel model combining electrical machine, power converter, load and control with programming language is demonstrated through simulations. A PI controller is used for controlling the voltage of the generator. The results presented show that the controller exhibits accurate tracking control of load voltage under different operating conditions. This demonstrates that the proposed model is able to perform an accurate control of the generated output voltage even in transient situations. The simulation is performed to choose the control parameters and study the performance of switched reluctance generator prior to its actual implementation. Initial experimental results are presented using NI-Data acquisition card to control the output power according to load requirements.
  PubDate: 2013-03-01
Structural dynamic analysis of the orbiting scroll wrap in the scroll compressor
- Abstract: Abstract A deep analysis of orbiting scroll wraps was conducted in this paper by using ANSYS and SolidWorks. Through the modal analysis, the involute of the circle profile orbiting scroll wrap demonstrated a large span in natural frequencies, which led to more superiority in avoiding structural resonances. Based on the dynamic harmonic analysis, loads of frequency changes were gained and the stress and strain distribution of the orbiting scroll wrap in the most dangerous working conditions were obtained, which determined the segments with maximum stress and strain-displacement properties. Two paths defined to elucidate further the structural characteristics of the exhaust chamber provided evidence for the initial correction of orbiting wraps. The results of the present study offer a theoretical basis for the design and manufacture of scroll wraps, and providing a new way to evaluate different scroll wraps.
  PubDate: 2013-03-01