Analytical Modeling and Pole–Slot Combination Selection Analysis of a Direct-Drive Drilling Permanent Magnet Synchronous Motor

Abstract

The pole–slot combination is an important factor affecting the cogging and electromagnetic characteristics of a permanent magnet synchronous motor. Taking a 95 kW direct-drive drilling permanent magnet synchronous motor (DPMSM) as an example, this paper presents an analytical model of the motor’s magnetic field based on the ideas of segmental discretization and magnetic vector potential, and considers a case in which the stator slot type is a closed slot. The Laplace or Poisson equations of each solution domain are solved using the separation of variables method, and the undetermined coefficients in the general solution are obtained by combining the boundary or interface conditions, thus completing the construction of the analytical model of the motor. The accuracy of this analytical model is verified with the finite element method (FEM). Based on the analytical model, the effects of the different pole–slot combinations on the electromagnetic performance, such as the air-gap flux density, back-EMF, cogging torque, output torque, etc., are investigated, and a reasonable choice of pole–slot combinations is made. The test results of the prototype are basically consistent with the predictions of the analytical model. The analytical model serves as an accurate and efficient calculation tool for the design of DPMSMs.