Principle of Torque-Axis Alignment in New Asymmetric PM Synchronous Reluctance Machines: Toward Less-Rare-Earth PM Machines

This article reveals the principle of a new torque-axis alignment technique as the basis for a new class of asymmetric permanent magnet synchronous reluctance machines (PMSynRMs). These machines are characterized by having distinct permanent magnet (PM) and SynRM poles. The objective is to precisely align peak torque from each pole type by adjusting the relative shift angle, minimizing the rare-Earth PM usage. A new analytical model is proposed, segregating torque generated by each pole type in a rotating dq reference frame. The impact of PM pole configuration—surface PM (SPM) and interior PM (IPM)—is examined, and the effects of cross-coupling and saturation are investigated. Two different torque separation models are used to describe key torque characteristics of the machines. The analysis indicates that the asymmetric IPMSynRM and SPMSynRM offer the same torque rating at a significantly lower PM volume usage compared with the conventional PM-assisted synchronous reluctance machine (PMaSynRM). In addition, it is observed that asymmetric IPMSynRM exhibits superior torque performance compared with asymmetric SPMSynRM, attributed to additional reluctance torque generated by IPM poles. Finally, a prototype is manufactured and tested to evaluate the presented principle in the asymmetric topologies.