Analysis and Design of Stator Combined Excitation Synchronous Machines With Special Winding Patterns and Toroidal Concentrated Coils

This paper studies motors that are part of a general class of synchronous machines with stator-reluctance rotor combined excitation. These machines, unlike the conventional implementations, including those that may be referred to in recent literature as of the flux-switching, variable flux reluctance, or flux-reversal type, employ a special winding pattern where only one coil side faces the airgap. The active stator has circumferentially magnetized spoke-type PMs and concentrated toroidal coils for improved slot fill and shortened end turns. A systematic approach for the analysis of the permeances, MMF produced in the stator, and open-circuit airgap flux is presented using an “associated half airgap” concept, which allows for reduced computation. A generally applicable method to establish the synchronous nature of such machines is documented. Unique nonlinearities and non-salient behaviors are exposed, and the torque generation in this machine is explained through the coenergy. Experimental characterization is carried out to validate finite element analysis (FEA) results, and the prospect for reliable high-power, high-efficiency operation in this motor topology is shown for a prototype.