An Innovative Semi-FEA Based, Variable Magnet-Step-Skew to Minimize Cogging Torque and Torque Pulsations in Permanent Magnet Synchronous Motors

This article proposes a new magnet step-skew approach for surface mounted permanent magnet (PM) motors in order to reduce the cogging torque and torque pulsations as well as to increase the output torque quality. The proposed approach based on semi finite element analysis (FEA) relies on varying both the length of the magnet segments and the angle between the rotor segments. The proposed method targets to optimize the magnet length and the skew angle so as to achieve minimum torque pulsations as opposed to the conventional magnet step-skew approach in which the magnet length and the skew angle are kept the same. Semi-2D-FEA based simulations with an optimization algorithm are completed to attain the optimum magnet geometries as well as the skew angles. 3D-FEAs are also performed for optimized design to check the reliability of the proposed approach. A prototype motor is developed using the proposed design approach, tested and verified. A detailed comparison between the proposed novel approach and the test data are also provided. It is confirmed that the new approach provides very practical results and performs well compared to conventional step-skew approach.