Due to the tradeoff between flux regulation range and on-load demagnetization withstand capability, the overall efficiency improvement of the conventional series-type variable flux memory machine (VFMM) is relatively restricted. Thus, this paper proposes a novel asymmetric-permanent-magnet VFMM (APM-VFMM) with an anti-demagnetization airspace barrier design to address the abovementioned issues. The proposed machine is geometrically derived from a double-layer permanent magnet (DLPM) series-type VFMM, in which the APM design can further extend the flux regulation range. Meanwhile, a satisfactory on-load demagnetization withstand capability can be also achieved with additional airspace barriers at two sides of the low-coercive-force (LCF) PM. Consequently, an effective overall efficiency improvement can be realized. First, the machine topologies, operation principles, and magnetic circuit models of the conventional DLPM-VFMM and proposed machine are comprehensively introduced, respectively. Then, the electromagnetic characteristics of the two machines under different magnetization states (MSs) are investigated, which confirm the merits of the proposed APM-VFMM particularly in terms of more significant efficiency improvement over a wide speed range compared to the conventional structure..
 

Anti-demagnetization airspace barrier; asymmetric permanent magnet; memory machine; series magnetic circuit, variable flux.