Optimization of Common-Mode Current Elimination in Four-Wire Inverter-Fed Motor through a Transfer Function Approach

Abstract

An optimized filter topology for four-wire electric-drive systems is proposed with small size, low loss, and large common-mode (CM) current elimination. The reason of the less CM current in a four-wire electric-drive system is well explained through analysis of the transfer function between inverter output voltage and cable input or neutral voltage. In a four-wire system, the impedance of electric machine also plays a significant role in further reducing CM current, however, it can be also related to the increase of CM current in some low frequencies. Based on this, an optimized topology placed on the neutral line of the four-wire electric-drive system is designed for the compensation of this weakness. The specific design procedure for the optimized topology is proposed through analysing relevant transfer functions while considering the practical situation of application. According to the experimental validation, the filter topology can reduce the CM current in the lower frequency range while maintaining a small value of CM current in higher frequencies. This is reached by causing a little bit power loss. The method of analysis through transfer function approach was validated in this work and can benefit further studies.