Rotor saliency improved structural design for cost reduction in single-phase line-start permanent magnet motor

This paper presents a study on motor material cost reduction by emphasizing rotor structural advantage in machine performance promotion of a single-phase line-start permanent magnet motor (LSPMM). The cost reduction of LSPMM is focused on saving high-price PM material in the LSPMM design. In the paper, a double-layer interior-PM (IPM) rotor structure is finally adopted to create higher rotor saliency ratio for improving reluctance torque generation to compensate decreased magnet torque due to PM usage reduction. That is, the hybrid torque with higher balance ratio of reluctance toque to magnet torque helps to lower the dependency o PM materials usage. With given torque and efficiency constrains, a series of double-layer rotor structures are built and optimized with gradually reduced amount of PM material. The torque and efficiency performances of LSPMM are predicted by using equivalent circuit method coupled with finite element analysis (FEA). The computed motor torque and efficiency performances are confirmed by comparing with test results.