Study of a High-Efficiency Series–Parallel-Connected Hybrid-PM Variable-Flux Permanent Magnet Synchronous Machine

Variable-flux permanent magnet synchronous machines (PMSMs) are considered as a promising candidate in electric vehicle industry for their ability to operate in a wide speed range with high efficiency by manipulating the magnetization state dynamically. A novel high-efficiency series–parallel-connected hybrid-PM variable-flux PMSM is proposed in this article. The topology and operating principle are introduced. The performances, including magnetization/demagnetization ability, PM stability, and torque ability, are analyzed and compared with other hybrid-PM variable-flux PMSMs. The results show that the proposed machine retains the advantages and overcomes the limitations of the existing structures. The steady-state efficiency-maximizing magnetization state adjustment strategy is proposed and evaluated. The torque-speed range is expanded and the proportion of high-efficiency region increases obviously by using this strategy. The efficiency-maximizing magnetization state adjustment strategy considering magnetization state adjustment loss is proposed and evaluated with the worldwide harmonized light vehicles test cycle (WLTC). The efficiency during the whole driving circle is significantly improved by adopting the proposed strategy.