Sensorless PMSM Drive with Large DC-link Voltage Fluctuation

This paper realizes a high power factor, high reliability, and low cost PMSM drive system with small DC-link capacitor. Compared with conventional bulky electrolytic capacitor for the regulation of DC-link voltage, a small-size film capacitor with capacitance reduction to 1% is used to realize a seneorless PMSM drive with high power factor, high reliability, and high compactness. To overcome high DC-link voltage fluctuations due to the small capacitor, the d-q axis current commands are modified according to the measured dc-link voltage and a power factor derived torque control strategy. A dc-link voltage feed-forward compensation scheme is used to minimize speed ripples due to the large voltage fluctuation effect. Simulation results show that design compromise between power factor, dc-link voltage ripple ratio, and speed ripple ratio can be achieved for practical design considerations. Experimental results of a sensorless PMSM drive in rated condition with a measured power factor of 97% with a reduction of dc-link capacitance to 1% have been obtained.