Analysis and Design of Synchronous Machines with Reluctance Rotor and PM Stator Combined Excitation

This paper studies motors that are part of a general class of synchronous machines with stator-only excitation including those that may be referred to in recent literature as of the flux switching, variable flux reluctance, or hybrid excitation type. In the studied example machine, the active stator has circumferentially magnetized spoke-type PMs and concentrated toroidal coils for improved slot fill and shortened end turns. A systematic analysis of the mmf produced by the toroidal coils in the stator and open-circuit airgap flux is developed to define feasible polarities of this synchronous motor and to establish that the dominant pole pair number is a consequence of the number of rotor protrusions. Several methods are employed for determining the d- and q-axes inductances and it is shown that the machine displays a non-salient behavior despite its castellated rotor. Analytical calculations and the 2-D FEA results are validated using experimental results obtained from the motor prototype.