Motor modeling for EMC simulation by 3-D electromagnetic field analysis

A building technique of high-frequency motor models by 3-D electromagnetic field analysis has been developed to establish the simulation technology for EMC estimation in the design stage of motor drive systems. Stray capacitance of each part of a motor was calculated by static electric field analysis, while inductance and resistance of its stator windings were calculated by magnetic field analysis. A motor equivalent circuit was then built with these circuit constants to compute frequency characteristics of motor impedance. In order to take eddy current in laminated iron core into account precisely, we analyzed a 3-D model of half thickness of one laminated steel sheet, and a simplified 3-D model of coil end of a motor. We also took the difference between magnetic field distribution of common mode and that of differential mode into account by setting different coil current and boundary conditions in the analyses. The frequency dependence of calculated inductance and resistance was introduced into circuit simulations. As a result, we have obtained frequency characteristics of motor impedance, whose basic features are similar to those of measured data. Possible causes of the discrepancy have also been discussed.