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Analysis of DC Winding Induced Voltage in Wound-Field Flux-Switching Machine with Air-Gap Field Modulation Principle

In this paper, the direct current (DC) winding induced voltage in wound-field flux-switching (WFFS) machines is qualitatively analyzed with air-gap field modulation principle. Operation principle and effective harmonics of DC winding induced voltage are modelled and deduced. It is found that only air-gap field harmonics with specific spatial orders, which numerically equals to odd times of half stator poles, can contribute to DC winding induced voltage. Harmonic order of DC winding induced voltages under open-circuit only, armature reaction only, and on-load condition, are predicted for m-phase WFFS machines with any feasible stator/rotor pole number combinations. Different armature winding configurations, including concentrated winding and distributed winding, are also analyzed and compared using the winding factor. Finite element analysis is employed to verify the prediction results. Finally, a prototype is built and tested for validation.