Mitigation of DC-Link Current Ripple for Dual Three-Phase Flux-Adjustable Hybrid PMAC Drives Using Collaborative Switching Strategy

In this article, the control scheme and switching strategies are studied for a dual three-phase hybrid permanent-magnet alternating current (PMAC) motor drive. Both high-coercive-force permanent magnets NdFeB and low-coercive-force permanent magnets AlNiCo are mounted on the rotor in order to provide high torque density and adjustable flux for electrical machine. The asymmetric dual three-phase windings can share the large currents for magnetization or demagnetization of AlNiCo, while offering low torque ripple and high fault-tolerant capability in the drive. The operation principle of the dual three-phase hybrid PMAC drive is presented in detail. In particular, a collaborative switching strategy is proposed for the drive based on five-segment space vector modulation. By optimizing the switching sequences of the two three-phase inverters collaboratively, the proposed switching strategy can mitigate the dc-link current ripple effectively under both normal loading condition and flux-tuning processes. Both theoretical analysis and experimental results are given to verify that the proposed switching strategy offers better performance in suppressing the dc-link current ripple compared to previous strategies. It facilitates overcoming the challenges of large current stresses in dc-link capacitors of flux-adjustable PMAC drives.