Design of Doubly Complementary Stator-PM Machine With High Magnet Utilization Factor for Low-Cost Applications

Aiming to improve permanent magnet (PM) utilization factor, suppress cogging torque, and reduce back-EMF harmonics in stator-PM machines, a new type of stator-PM doubly complementary machines (DCMs) are proposed in this paper. These machines employ two complementarities in the structure, as one exists in double rotors and the other exists in the units belonging to same phases. The first complementary characteristic supplies a consecutive switching path for PM exciting flux, so that shorted or open magnetic path could be avoided to reduce cogging torque and improve PM utilization. The second one is designed to reduce back electromotive force (EMF) harmonics and improve the torque density. The topology, operation principle, characteristics, and design methodology for DCMs are presented. Simulation and experiments are conducted for a 12/11(stator teeth/rotor teeth) DCM to evaluate its performance and verify this design methodology. It is revealed that this machine could obtain good sinusoidal back-EMF waveform, small torque ripple, and high PM utilization factor due to the doubly complementary characteristic.