A Field-Superposition Model for Fast Electromagnetic Performance Prediction of PM Machine With Irregular Magnets and Irons

Accurate and fast prediction of air-gap magnetic field is critical for the design and optimization of spoke-type PM machines especially those with high slot/pole number and irregular-shape magnets. Conventional field-superposition analytical model is a fast computation method for electromagnetic performance prediction of PM machines, however, it can not be directly utilized in the spoke-type PM machines with irregular magnets and interpolar irons. In this paper, an improved field-superposition method based on segmented virtual domains is proposed to achieve high-precision and fast magnetic field prediction of the spoke-type PM machine accounting for irregular magnets and interpolar irons. The number of domains requiring modeling can be reduced effectively to save computation time, and the inter-layer magnetic resistance of the interpolar iron can be taken account for high precision by the improved field-superposition method. Firstly, the schematic structure of one spoke-type PM machine with quasi-trapezoidal magnet and quasi-triangular iron is presented, and the major features of the proposed analytical modeling method is discussed and compared with conventional superposition method. Secondly, by taking advantage of the segmented virtual-domain method along with half-range Fourier series expansion, the open-circuit air-gap field with and without stator slots, the back electromotive force and the torque output of the electric machine are formulated mathematically. Finally, the finite-element method is conducted on the electromagnetic performance calculation to validate the improved field-superposition method. The results show that the analytical model agrees with the numerical results well, and the computation time can be reduced from 92s to 0.631s.