Impedance Based Beat Suppression Strategy for PMSM Drives with Small DC-Link Capacitors

This paper investigates the beat phenomenon in permanent magnet synchronous motor (PMSM) drives with small DC-link capacitors caused by the interactions of the fundamental current and the DC-link inspired harmonics. The harmonics in the beat current are analyzed in an impedance perspective, and a beatless control strategy is proposed by reshaping the impedance of the PMSM drive system at dominated harmonics. Different from the existing beat suppression methods focused on the pulse width modulation (PWM), the proposed impedance-based beatless control strategy can suppress the low-frequency envelop in motor current effectively without aggravating the LC resonance of the system. By generating the damping currents at the dominated harmonics on motor current vector, the small signal model of the system is immune to the variation of the steady state values, which ensures the validity of the beat suppression over a wider operating range. Experimental results show the effectiveness of the proposed method in a prototype of PMSM drive with small DC-link capacitors.