A Design of PWM Inverter Passive Filter Based on CM Transformer

Abstract

The negative effects of the PWM inverter are mainly as follows: the high dv/dt value of the DM(differential mode) and the CM(common mode) voltage will cause an impact on the insulation layer of the motor winding; the current generated by the CM voltage on the motor bearing will corrode the bearing and reduce motor life; electromagnetic interference caused by high frequency CM leakage current will affect the stability of the system. Based on the CM transformer, a new passive filter topology is proposed, this filter uses the coupling function of the CM transformer to suppress the CM voltage and the leakage inductance of the CM transformer as the DM filter inductor, which can effectively suppress the dv/dt values of the DM and CM voltages, it can also effectively reduce the RMS value of the CM voltage. In this paper, the winding method of CM transformer windings is improved, each winding is divided into two parts in series and distributed symmetrically on the iron core, which makes the leakage inductance and coupling coefficient between the windings of the transformer more symmetrical, which enhances the filtering effect. The effectiveness of the filter is verified by simulation and experiment.