Improved Cogging Calculation Methods for Surface Mounted Permanent Magnet Synchronous Motors

As part of the design process of surface mounted permanent magnet synchronous motors (PMSM), a combination of analytical calculation and finite element analysis (FEA) is proposed for the cogging torque calculation. The analytical methods are recommended for the initial design iterations in view of their high computational speed. In general, however, finite element analysis is more accurate and is therefore recommended for the final design iterations. In order to obtain continuity when switching from analytical calculations to FEA, two modifications are made to the equations upon which the analytical methods are based in order to improve accuracy. This is demonstrated by comparing the results from the unmodified and modified analytical method with those using the finite element method through their application using the nominal parameters of a Control Techniques Dynamics CTD 142UMC300 motor. Air-gap flux density calculations are compared as well as cogging torque calculations.