Reduction of Computational Efforts to Obtain Parasitic Capacitances Using FEM in Three-Phase Permanent Magnet Motors

The rise in demand for electric and hybrid vehicles, the issue of bearing currents in electric motors has become increasingly relevant. These vehicles use inverters with high frequency switch that generates the common mode voltage and current, the main factor responsible for bearing issues. In the machine structure, there are some parasitic capacitances that exist inherently. They provide a low impedance path for the generated current, which flows through the machine bearing. Investigating this problem in practical scenarios during the design stage is costly and requires great effort to measure these currents. For this reason, a strategy of analysis aided by electromagnetic simulation software can achieve desired results in terms of complexity and performance. This work proposes a methodology using Ansys Maxwell software to simulate two-dimensional (2D) and three-dimensional (3D) model of a three-phase permanent magnet motor with eight poles. The 2D model was used to obtain the parasitic capacitances in the motor plane, and the 3D model was used to acquire the coil head or end-winding effect capacitances. The proposed methodology is capable of predicting favorable results in terms of measuring capacitive bearing currents using a voltage pulse as an input source. The great contribution of this work is the computational reduction of the calculation of parasitic capacitances and the implementation of the machine's common mode circuit to predict the bearing and common mode currents.