Current Issue : October - December Volume : 2013 Issue Number : 4 Articles : 6 Articles
Distributed generation (DG) is deeply changing the existing distribution networks which become very sophisticated and complex\r\nincorporating both active and passive equipment. The simplification of their management can be obtained assuming a structure\r\nwith small networks, namely, microgrids, reproducing, in a smaller scale, the structure of large networks including production,\r\ntransmission, and distribution of the electrical energy. Power converters in distributed generation systems carry on some different\r\nancillary functions as, for example, grid synchronization, islanding detection, fault ride through, and so on. In view of an optimal\r\nutilization of the generated electrical power, fault tolerant operation is to be considered as a suitable ancillary function for the\r\nnext future. This paper presents a complete modeling of fault tolerant inverters able to simulate the main fault type occurrence\r\nand a control algorithm for fault tolerant converters suitable for microgrids. After the model description, formulated in terms of\r\nhealthy device and leg binary variables, and the illustration of the fault tolerant control strategy, the paper shows how the control\r\npreserves power quality when the converter works in the linear range. The effectiveness of the proposed approach and control is\r\nshown through computer simulations and experimental results....
Different energy sources and converters need to be integrated with each other for extended usage of alternative energy, in order to\r\nmeet sustained load demands during various weather conditions. The objective of this paper is to associate photovoltaic generators,\r\nfuel cells, and electrolysers. Here, to sustain the power demand and solve the energy storage problem, electrical energy can be\r\nstored in the form of hydrogen. By using an electrolyser, hydrogen can be generated and stored for future use. The hydrogen\r\nproduced by the electrolyser using PV power is used in the FC system and acts as an energy buffer.Thus, the effects of reduction and\r\neven the absence of the available power from the PV system can be easily tackled. Modeling and simulations are performed using\r\nMATLAB/Simulink and SimPowerSystems packages and results are presented to verify the effectiveness of the proposed system....
New hybridmodel for efficiency optimization of inductionmotor drives (IMD) is presented in this paper. It combines two strategies\r\nfor efficiency optimization: loss model control and search control. Search control technique is used in a steady state of drive and\r\nloss model during transient processes. As a result, power and energy losses are reduced, especially when load torque is significant\r\nless related to its rated value. Also, this hybrid method gives fast convergence to operating point of minimal power losses and shows\r\nnegligible sensitivity to motor parameter changes regarding other published optimization strategies. This model is implemented in\r\nvector control induction motor drive. Simulations and experimental tests are performed. Results are presented in this paper....
The impact of the rotor slot number selection on the induction motors is investigated. Firstly, analytical equations will reveal the\r\nspatial harmonic index of the air gap magnetic flux density, connected to the geometrical features and the saturation of the induction\r\nmotor. Then, six motors with different rotor slot numbers are simulated and studied with FEM. The stator is identical in all motors.\r\nThe motors are examined under time-harmonic analysis at starting and at 1440 rpm. Their electromagnetic characteristics, such\r\nas electromagnetic torque, stator current, and magnetic flux density, are extracted and compared to each other. The analysis will\r\nreveal that the proper rotor slot number selection has a strong impact on the induction motor performance....
Results from the magnetization of an 80 kVA power transformer, using a directly coupled nonfiltered three-phase voltage-source\r\ninverter (VSI), are presented. The major benefits of this topology are reduction in switching filter size as well as filter losses.\r\nDrawbacks include higher stress on the transformer windings and higher transformer magnetization losses. In this paper, the\r\ntotal magnetization losses are presented for different voltage levels. The transformer has been magnetized with the rated frequency\r\nof 50Hz at various voltage levels. The saturation characteristics as well as the magnetizing resistance are derived as functions of the\r\nvoltage.These are used as inputs for the simulations.Themagnetization losses have been experimentallymeasured and simulated for\r\nthree different DC levels. Results fromthe simulations show good agreement with the experimental results. As expected, the pulsed\r\nvoltage waveforms generate larger magnetization losses than the corresponding 50Hz case. The losses are strongly dependent on\r\nthe DC level....
?e development of the smart grids leads to new challenges on the power electronics equipment and power transformers. ?e\r\nuse of power electronic transformer presents several advantages, but new problems related with the application of high frequency\r\nvoltage and current components come across. ?us, an accurate knowledge of the transformer behavior in a wide frequency range\r\nis mandatory. A novel modeling procedure to relate the transformer physical behavior and its frequency response by means of\r\nelectrical parameters is presented. Its usability is demonstrated by an example where a power transformer is used as ??lter and\r\nvoltage reducer in an AC-DC-AC converter....
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