Design considerations and parameter optimization of stator wound field synchronous machines based on magnetic the gear effect

Stator wound field synchronous machines (SWFSMs) are gaining more and more research and application interest recently due to the absence of expensive rare earth magnet materials. These machines are characterized by a doubly salient structure, and both the DC field winding and the three phase armature windings are located in the stator. In this paper, taking the basic structure of stator DC excited vernier reluctance machine, which is one type of SWFSM, the design of SWFSMs are studied in detail semi-analytically, by finite element analysis (FEA), and also validated by experiment. First, the effects of stator/rotor slot combinations on performances, including cogging torque, torque and torque ripple, voltage fluctuation of the DC winding are analyzed and compared. Then, the back-EMF, torque and power factor expressions in terms of the geometrical variables are proposed. Also, a 12-stator-slot, 11-rotor-slot machine as an example, the design parameters, including the split ratio, the air gap length, the proportion of the armature and field coil turns in one stator slot, and the stator/rotor tooth arc combination are optimized. The optimization results show that these design parameters have a various influence on electromagnetic performance, and the designers should select the design parameters comprehensively.