Multi-Segment Magnetic Flux Path Analysis of Wound-Field Flux-Switching Machines with Different Winding and Stator-Rotor Combinations

Wound field flux switching machine (WFFSM) showcases attractive features such as a robust rotor structure, variable field operation capability, and no risk of demagnetization. The WFFSM also provides an integrated stator structure that accommodates both field and armature windings, while the rotor does not require windings or magnets. However, having both windings on the stator creates long and inefficient magnetic flux paths at specific rotor positions that do not directly contribute to electromagnetic torque generation. Therefore, it is imperative for WFFSMs to thoroughly investigate the magnetic flux paths associated with the stator bridge structure. This paper employs a multi-segment magnetic equivalent circuit to identify these longer magnetic flux paths, validated through finite element analysis. In addition, their impact on inductance and torque production of WFFSMs with different winding configurations as well as stator-rotor pole combinations. Torque segregation and energy conversion loop analysis are conducted to visualize and quantify the impact of the longer magnetic flux paths on electromagnetic performances. The study reveals that the inductance harmonics originating from the integrated stator structure generate a negative reluctance torque, decreasing the net output torque. The results demonstrate that the WFFSM employing a circumferential field and armature winding configuration, which does not suffer from the longer magnetic flux path, achieves the highest output torque. It exhibits an output torque 57% higher than the WFFSMs suffering from the longer magnetic flux path, with identical volume.