Detent Torque Analysis of Multi-stator-module Permanent Magnet Arc Machine Based on a Hybrid Analytical Model Considering Asymmetric Stator and Rotor Eccentricity

This article proposes a hybrid analytical model for detent torque analysis of multi-stator-module permanent magnet (PM) arc machine (MSM-PMAM) considering the asymmetric stator and rotor eccentricity. The detent torque equation-based model is used to derive a general design principle of MSM-PMAM with reduced detent torque, while the harmonic magnetic field-based model is used to reveal the generation mechanism of detent torque. The cogging torque and end torque are derived, and a general design method for MSM-PMAM to reduce the detent torque is proposed, which is verified through finite element analysis (FEA). Then, a unified model for both stator-PM and rotor-PM machine is established to reveal the generation mechanism of detent torque considering harmonic magnetic fields for circular machines. The detent torque characteristics of MSM-PMAM are derived by introducing a “equivalent slot” concept and the influence caused by asymmetric stator modules and rotor eccentricity is also analyzed. A three-stator-module PMAM is designed and the detent torque is analyzed based on an improved Schwarz-Christoffel mapping method. The experimental and FEA results validate the correctness of the proposed method and analysis.