Investigation of a Parallel Hybrid Excitation Machine With Auxiliary Winding for Loss Reduction in Flux-Weakening Operation

An axial-parallel hybrid excitation machine (APHEM) with an auxiliary winding is proposed and investigated for loss reduction in the flux-weakening operation. The permanent magnet (PM) flux and wound field flux of the APHEM are different and coupled under the armature action. Based on the axial-parallel structure, an auxiliary winding is introduced into the PM part to make better utilization of the distinct PM flux. Because of the coupling of the two fields, this auxiliary winding not only couples the PM flux but also affects the wound field flux. Two major conclusions can be derived from the theoretical analysis. First, the auxiliary winding couples the PM flux and produces extra torque, benefiting a smaller field current. Second, the auxiliary winding can suppress the phase voltage because of the larger characteristic current of the PM part than the wound field part. This facilitates a smaller d-axis armature current. The reduced currents favor the reduction in copper loss and core loss. Compared with the original APHEM under the minimum-copper-loss control, the proposed method achieves a 34% reduction in the maximum loss and a 60% decline in the maximum torque ripple ratio. Finally, the measured results verify the analysis.