Topology and PWM method dependency of high frequency leakage current characteristics of voltage source inverter driven AC motor drives

Abstract

In PWM inverter based AC motor drives, high frequency common-mode voltage (CMV) causes high frequency common-mode current (CMC, motor leakage current). With its magnitude reaching ampere levels, the CMC can induce bearing failures, drive nuisance trips, EMC issues etc. The CMC is dependent on the inverter topology (two or three-level), PWM method (pulse pattern), and the filters if active/passive mitigation methods used. This paper investigates the CMV/CMC properties of the two and three-level VSIs [with and without common-mode inductor (CMI)] for various PWM methods. It shows the peak CMC is highly dependent on the PWM method and pulse sequence (in addition to dv/dt). The PWM methods pulse pattern and sequence analyses are supported by detailed experiments to illustrate that the reduced CMV PWM methods with proper pulse sequences yield low peak CMC and the inclusion of a CMI filter provides further suppression. Furthermore, the high frequency CMV/CMC spectra for various PWM methods are provided comparatively. It is shown that when the common-mode resonant frequency coincides with the dominant CMV frequency, the CMC can be amplified. As a result a comprehensive leakage current evaluation is provided in the paper. The information is useful for design and implementation of motor drive PWM algorithms and high frequency EMC filters in terms of CMV/CMC performance considering CMV/CMC reduction.