Cogging torque minimisation of novel switched flux permanent magnet memory machine by structural variation

A novel switched flux permanent magnet memory machine (SF-PMMM), featuring high torque density, expedient thermal dissipation, and exceptional mechanical robustness, is proposed, where the adoption of inherently low coercivity magnet material-aluminium-cobalt-nickel (AlNiCo) enables the flexible online controllability of air-gap flux by simply imposing a transient current pulse, thereby it is potentially applicable for automotive, aerospace and servo applications. However, due to the doubly saliency of stator and rotor cores, the resultant large torque ripple is highly undesirable for high-precision drive system. In this paper, two techniques based on structural variations, without resorting to complicated skewing, are developed to mitigate the cogging torque. Additionally, an analytical explanation is theoretically addressed to provide a comprehensive insight into the cogging torque suppression in design stage of this machine. The validity of the proposed techniques are comprehensively analysed and quantitatively compared by employing time-stepping finite-element-method (TS-FEM). With the consideration of the particular online magnetization of magnets, a new optimal combinative technique is presented for the cogging torque minimisation of the machine without compromising torque capability and complicating manufacturability, and the on-load torque characteristic and the back-electromotive-force (EMF) are also evaluated to confirm the superiority of the combinative technique.