Analysis of Excitation Winding Induced EMF in Non-Overlapped Stator Wound Field Synchronous Machines

Different from the induced electromotive force (EMF) in armature winding, the induced EMF in excitation winding is detrimental to the performance of wound field synchronous machines by causing unstable excitation field and thus extra torque pulsation and losses. Moreover, it also imposes challenges to machine control, particularly for high-speed operation. This article investigates the induced EMF in the excitation winding of 3-phase non-overlapped stator wound field synchronous machines (SWFSMs). It has revealed that the amplitude of the excitation winding induced EMF is largely dependent on the slot-pole combination. Therefore, with suitable slot-pole combinations, the induced EMF issue will be significantly alleviated by eliminating low-order induced EMF harmonics. Although the excitation winding induced EMF can also be reduced by passive techniques, e.g., optimization and shaping of rotor pole arc, the average torque will be greatly degraded as well. Finally, the finite element predictions are validated by measurements on two prototyped non-overlapped SWFSMs.