Eliminating Common Mode Voltage and Suppressing Conducted EMI Based on Discontinuous PWM for General Two-Unit PMSMs

Abstract

In high-power motor drive systems, the two-unit permanent magnet synchronous motor (PMSM) system driven by parallel inverters controlled by pulse width modulation (PWM) will generate significant common mode voltage (CMV) and conducted electromagnetic interference (EMI), which will have adverse effects on the system. In order to minimize this adverse effect, this paper proposes a modulation strategy based on discontinuous PWM (DPWM) that can completely eliminate the CMV of the two-unit PMSM to ground. This strategy selects only one zero vector within each carrier cycle and makes the switching states of the parallel inverters three “1” states and three “0” states at any time, significantly suppressing conducted EMI. The PWM waveforms within each carrier cycle are symmetrical, which significantly reduces the total harmonic distortion (THD) of the motor phase current compared to asymmetric PWM waveforms. The principle of the proposed strategy is introduced and the resulting switching loss of inverters is analyzed. The impact of deadtime is discussed, and the edges of PWM signals are improved to eliminate the CMV spikes caused by deadtime. The experimental results are provided to verify the effectiveness of the proposed strategy.