On the Contribution of PWM Methods to the Common Mode (Leakage) Current in Conventional Three-Phase Two-Level Inverters as Applied to AC Motor Drives

This paper experimentally investigates the common mode voltage (CMV) and common mode current (CMC, leakage current) characteristics of various PWM methods for the classical two-level three-phase voltage source inverter (VSI) as applied to induction motors. The classical SVPWM and DPWM methods which have high CMV/CMC, and the recently proposed reduced CMV (RCMV) PWM methods, such as NSPWM and AZSPWM1 are considered. The effect of including the low cost industry solution of the common mode inductor (CMI) for CMC reduction is investigated. Furthermore, the dependency of the CMC on the inverter topology is investigated by the experimental evaluation of a commercial three-level neutral-point-clamped (NPC) VSI. Based on the experimental results, it is shown that it is beneficial to employ high performance RCMV-PWM methods for the purpose of CMV/CMC reduction. It is shown that including a small CMI further enhances the CMC performance of a drive. Such a configuration provides comparable CMC performance to that of a three-level NPC-VSI and it is more favorable as it is more economical and efficient. The experiments involve a 4-kW, 4-pole induction motor driven by a two-level VSI and a three-level NPC-VSI with diode rectifier front-ends supplied from the three-phase 400 V, 50 Hz power line.