Abstract: A global analytic model for the electromagnetic field of surfacemounted permanent magnet motor is established by using Fourier series method and the noload and load electromagnetic characteristics of the motor are analyzed. In 2D polar coordinate system, the solution domain of the motor is divided into five subdomains: permanent magnet, air gap, armature slot, stator slot opening and auxiliary slot. The Laplace equation or Poisson equation for each subdomain is solved with variable separation method, and the harmonic coefficients in the general solution are determined according to boundary conditions, with the analytic expressions of each subdomain obtained. The electromagnetic parameters including the magnetic density in air gap, noload back EMF, cogging torque and electromagnetic torque are calculated, and the correctness of analytic method is verified by finite element analysis. On this basis, the influences of polar arc coefficient, auxiliary slot size and slot opening width on cogging torque and electromagnetic torque are studied. In addition, an analytic model for unequal slot openings matching is proposed to reduce cogging torque peak and electromagnetic torque ripple. The method can reflect the relationship between the designed motor performance and its size and parameters and can be used in the initial design and optimization of the motor.

Key words: permanent magnet motor, analytic method, finite element method, cogging torque, electromagnetic torque, unequal slot openings