A CSI-Fed PMSM Drive System With Single-Stage Operation for Extended Constant-Torque Range

Aiming at extending the constant-torque region, a high-performance single-stage control strategy is proposed for the current-source inverter (CSI) fed permanent-magnet synchronous motor (PMSM) drive system in this article. Different from traditional CSI-fed motor drives, both the dc-link current and the motor speed are regulated by the CSI for single-stage operation. A novel cascaded closed-loop control structure is proposed, where the speed controller and the dc-link current controller are designed as the outer and inner loops, respectively. The input dc voltage can be boosted for higher terminal voltages of PMSM, and the constant-torque operation range is extended and the efficiency is improved for the CSI-fed drive due to the avoidance of flux-weakening operation. Moreover, the cascaded closed-loop current controller is developed, which can suppress the LC resonance excited by low-order current harmonics in the single-stage operation. To achieve the smooth transition between the two-stage operation in the low-speed region and the single-stage operation in the high-speed region, a hysteresis comparator-based switching strategy is proposed. Experiments have been conducted to verify the effectiveness of the boost feature of CSI and the proposed control scheme.