Analysis of Cogging Torque of Permanent Magnet Motors Under Mixed-Eccentricity and Manufacturing Tolerances

The rotor eccentricity and manufacturing tolerances caused by unavoidable uncertainties in the process of manufacturing deteriorate the cogging torque of permanent magnet (PM) motors. To guide the design and optimization of PM motors, this paper proposes an analytical model to reveal the effects of mixed-eccentricity (ME) and manufacturing tolerances on the harmonic components of cogging torque. A coefficient is introduced to intuitively characterize the impact of ME on the distribution of the air-gap length. Then a modified analytical model is developed to theoretically identify the additional harmonic components (AHCs) of cogging torque associated with the eccentricity and tolerances. And the main AHCs of cogging torque are quantitatively determined through the finite element method. Finally, suggestions to improve the robustness considering uncertainties by selecting pole/slot combination and pole-arc ratio are proposed.