Current Ripple Suppression of PMSM Drives Under Reduced DC-Link Capacitance Considering Digital Delay

An ac-fed PMSM drive system with reduced dc-link capacitance easily suffers from fluctuations of dc-link voltage, which may aggravate modulation error and severe current ripple at low frequency. The occurrence and impact of the dc-link voltage fluctuations are discussed first. Then, a current ripple suppression method is proposed by the adoption of the improved modulation strategy, where the digital delay of dc-link voltage is compensated by the enhanced voltage observer (EVO). The EVO predicts the voltage two-switching-period ahead to eliminate the digital delay in the measured dc-link voltage. The accuracy and design of EVO are analyzed. The modulation index is updated based on the predicted average voltage of the EVO, which prevents the motor currents from voltage fluctuations and suppresses undesired current ripples. Finally, the proposed method is validated by simulation and experimental results. The proposed method could suppress the current ripples obviously under reduced dc-link capacitance, which consequently improves the power density of PMSM drives.