A Novel Series Magnetic Circuit Variable Flux Memory Machine With Self-Flux Leakage Paths

Variable flux memory machine (VFMM) applying low coercivity force (LCF) permanent magnets (PMs) is suitable for electric vehicles (EVs) since its air-gap flux can be adjusted easily. In this article, a novel series magnetic circuit VFMM with self-flux leakage paths (SMC-VFMM-SLP) is proposed, in which the design concept of self-flux leakage is introduced to enhance air-gap flux regulation (FR) range and keep high torque density simultaneously. The self-flux leakage paths can control the self-flux leakages based on the magnetization states (MSs) of the employed LCF PMs. The machine can thus keep a high torque density under the positive MS and achieve excellent flux-weakening ability under the negative MS when it is loaded. First, the topology and the FR range expansion principle of SMC-VFMM-SLP are interpreted in detail, in which the magnetic circuits under different MSs are qualitatively analyzed. The electromagnetic performance of SMC-VFMM-SLP under the positive and negative MSs is subsequently investigated by the finite element method, including no-load characteristics, torque abilities, and efficiency maps. Finally, an SMC-VFMM-SLP prototype is manufactured and measured, which confirms the feasibility of the proposed self-flux leakage paths design for the air-gap FR range improvement.