Suppression of DC-Link Current Ripple for Modular Multilevel Converters Under Phase-Disposition PWM

Abstract

The modular multilevel converter (MMC) is attractive for medium- or high-power applications because of its high modularity, availability, and high power quality. In this article, the dc-link current ripple of the three-phase MMC derived from the phase-disposition pulsewidth modulation and circulating current control is analyzed. A variable carrier phase-shifted angle control strategy under the two-group carriers-based modulation is proposed to suppress the dc-link current ripple of the three-phase MMC. Through the regulation of the carrier phase-shifted angles under the two-group carriers-based modulation in each carrier period, the high-frequency current injected into the dc link from the three phases of the MMC can be counteracted, which suppresses the dc-link current ripple of the MMC with simple algorithm, and therefore improves the dc-link power quality. Simulations and experimental studies of the MMC are conducted, and the results confirm the effectiveness of the proposed control strategy for the MMC.