Design and Evaluation of the Vienna Rectifier for a 5MW Wind Turbine System
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Electric power engineering (MPEPO), MSc
Publicerad
2013
Författare
Nikouei, Mojgan
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
This thesis is a part of a larger project that deals with the design of an offshore DC wind turbine system. The aim of this thesis is to design and evaluate the Vienna rectifier for a 5 MW wind turbine system (WTS) with a permanent magnet synchronous generator (PMSG). In order to estimate the efficiency and the maximum power of the rectifier’s generator that can be extracted, the power losses have to be calculated and suitable power electronic switches should be chosen. Finally, the results are to be compared with the performance of the diode rectifier and the conventional IGBT converter. Generally, the Vienna rectifier is applied to many applications with high switching frequency such as a power supply for an electronic system, especially for telecommunication devices. However, in this project, an effort is made to use it in a wind turbine system application, which has a low switching frequency. The idea behind is to enhance the pure diode rectifier and in this way extract more output power. Therefore, to investigate the performance of the Vienna rectifier and design it according to the project’s requirements, several steps have been done. In the first part, the rectifier operation is studied. The Vienna rectifier is a three phase, three levels and three-switch rectifier; it is a kind of PWM (Pulse Width Modulation) with a partly controlled output voltage. iv There is a midpoint N, between two equal dc voltages at the output DC bus voltage, which is considered as a reference point with zero voltages. Therefore, three different voltages, + !! ! , 0, - !! ! are available as output. Based on the phase current direction and the state of the switches, the phase potentials voltages could be determined. An important point in controlling of the Vienna rectifier is the phase displacement angle φ!. According to available literature, it has the limitation between (- ! !, + ! !). However, it is shown here that this is not completely true in this application. In the next part, the designs of the converter and the power as well as the loss calculation have been done. The circuit of the Vienna rectifier is simulated in the Simplorer software and all of the waveforms are exported to Matlab in order to do the calculations. The simulation results show that the Vienna rectifier has low losses partly due to a very low switching frequency. The IGBTs are turned on only twice during one line period. When the IGBT is in the ON state position during a half period, the output power that can be extracted is 5 MW with a 43° phase shift angle. This power is extracted when the output dc-link voltage has the value, 9100 V. As the Vienna rectifier can work in a wide voltage range, other dc voltages are examined. Simulations are performed for, 4300 V, 8400 V, 9100 V and as expected, the Vienna rectifier has the similar operation with diode rectifier at 4300 V. The pure diode rectifier that works with the same generator can only provides 2.5 MW if no extra capacitors are used. Due to usage of only three IGBTs in designing the Vienna rectifier, the voltage stress during blocking of power electronic switches would be reduced, as well as manufacturing cost, in comparison with the conventional IGBT converter.
Beskrivning
Ämne/nyckelord
Elkraftteknik , Electric power engineering