Uniform Distribution Spread-spectrum Modulation Strategy for MMC to Reduce Conducted EMI and Switching Loss

Modular multilevel converters (MMCs) have been widely used owing to their superior performance. However, the rapid switching of power electronics devices causes serious electromagnetic interference (EMI). There are a large number of obvious EMI peaks in the frequency spectrum of the carrier phase-shifted constant-switching-frequency pulse-width modulation (CSFPWM). Spreading the EMI across a wider frequency range can help to reduce the EMI peaks. In this study, we designed a uniform distribution (UD) spread-spectrum modulation technology using the principle of uniform switching frequency distribution and minimum switching loss for MMC. Its feasibility is verified by theoretical derivation and simulation. Then, the effectiveness of UDPWM in reducing the EMI is verified in experiments with a prototype MMC testbed in the lab. Compared with traditional CSFPWM, UDPWM can reduce conducted EMI by 10–20 dB. Also, compared with random PWM (RPWM), UDPWM can improve efficiency and reduce total harmonic distortion (THD) of output voltage and current in MMC.