Design and optimization of a novel wound field synchronous machine for torque performance enhancement

This paper presents the design and optimization of a novel wound field synchronous machine topology, in which permanent magnets (PMs) are introduced into the rotor slot opening with segment configuration for high quality output torque performance. The rotor shape of the proposed PM-assisted wound field synchronous machine with segment configuration is optimized for maximizing the average output torque and decreasing torque ripple under constant PM volume and motor size. The segment configuration can be benefit to improve the reluctance torque. In addition, it is further clarified that the assisted-PM can help to increase the field torque by enlarging the magnetizing synchronous reactance (X_f), as well as increasing airgap flux density. An optimal method combining Kriging method and genetic algorithm is applied for rotor shape optimization of proposed PM-assisted wound field synchronous machine (PMa-WFSM). Then, the 2-D finite-element analysis results, with the aid of JMAG-Designer, are used to confirm the validity. It is determined that the average output torque is improved by 31.66%, and keeps lower torque ripple without decreasing efficiency, increasing PM volume and motor size compared with those of the basic model. Finally, irreversible demagnetization and mises stress analysis verifies the reliability of the novel topology.