Common-Mode EMI Comparison of NSPWM, DPWM1, and SVPWM Modulation Approaches

Abstract

This paper provides a closed-form voltage harmonic analysis of Near-State Pulse Width Modulation (NSPWM) for a three-phase two-level voltage source inverter (VSI). NSPWM is a modulation technique that reduces common-mode voltage (CMV) magnitude up to 2/3 compared with conventional PWM. With the closed-form analysis, NSPWM’s impacts to CMV, common-mode current (CMI) and filter weight are compared with Space Vector PWM (SVPWM) and Discontinuous PWM (DPWM1[1]) in both the time and frequency domains. The comparison shows that NSPWM has lower CMV and CMI than SVPWM and DPWM1 over a wide frequency range. Experiments show that NSPWM reduces common-mode harmonics by up to 17 dB (7X), which leads to a 17% filter weight reduction. A system with 2-stage AC common-mode filter is tested with NSPWM and results meet DO-160G limit.