Analysis of the Unbalance of DC Link Voltage in 12-step Inverter with 2-Phase Chopper Preregulator

2상 쵸퍼 Preregulator를 갖는 12-step 인버터에서의 DC Link단 전압 불평형 해석

This paper deals with the voltage unbalance of DC link voltage in series connected two 6-step inverters with double chopper preregulator. Each output of the 6-step inverter is connected to each transformer. The secondary windings of one of the transformers is zig-zag connected and the other star connected. The secondary terminals of the two transformers are series connected which makes 12-step output voltage waveform. In this case, the characteristics of the two transformers are rather different each other. The difference results in the voltage unbalance of the two 6-step inverter input capacitor voltages which make the DC link voltage. The degree of the voltage unbalance is analysied with the variations of load power, load power factor and % impedance of the transformer.