A Novel Variable Flux Memory Machine With Separated Series--Parallel PM Structure

Variable flux memory machine (VFMM) with hybrid magnetic circuit (HMC) is regarded as a potent solution for electric vehicles owing to its flexible flux control and fine accidental demagnetization withstand capability. However, existing HMC-VFMMs generally suffer from insufficiently wide flux regulation range and relatively high magnetization current level, hindering overall efficiency enhancement, particularly under high-speed region. This article proposes a novel separated series–parallel VFMM (SSP-VFMM), which features that the used high-coercive-force and low-coercive-force magnets are placed in a dual-layer arrangement to form SSP magnetic circuits, respectively. The second permanent magnet layer employs different magnet materials in the same rotor hole, which alleviates the magnetic saturation so as to achieve an excellent flux regulation range, and maintain a satisfactory accidental demagnetization withstand capability. The topology structures and operating principles of the existing HMC-VFMM and the proposed SSP-VFMM are illustrated and introduced first, and then their performance metrics are analytically assessed by using magnetic circuit models. The electromagnetic characteristics of the two machines are subsequently evaluated and compared, including air-gap magnetic flux densities, torque characteristics, and efficiency maps. Finally, some relevant experiments on HMC- and SSP-VFMM prototypes are undertaken to verify the effectiveness of the proposed new topology.