On the Modeling of Bearing Voltage and Current in PWM Converter-fed Electric Machines Using Electromagnetic Finite Element Analysis

Bearing voltages and resulting currents in electric machines driven by PWM converters with fast switching and high $dv/dt$ can cause premature bearing failures. With the transition from conventional Si devices to wide bandgap (WBG) devices and increase in switching frequency, bearing voltages and currents become more significant and need to be addressed from the early design stage. This paper proposes to use coupled field-circuit electromagnetic finite element analysis (FEA) to model bearing voltage and current in electric machines, which takes into account the influence of distributed winding conductors and frequency-dependent winding RL parameters. The three known bearing current types are explained and modeled in a unified way by using the proposed approach with simple calculation examples. Potential bearing current issues in axial-flux machines, and possibilities of computation time reduction, are also discussed.