Modeling and Mitigation of Bearing Currents in Electrical Traction Drives

Inverter driven machines are a vital part of electrical traction drives. They are subject to high-frequency parasitic currents, caused by the high-frequency components of the pulse width modulated (PWM) voltage. These currents can flow through the bearings of the machine and cause severe damage. Additionally, the common-mode voltage of the inverter causes a voltage difference between the shaft of the machine and its housing. This work investigates these effects in one combined system model and shows the influence of different parameter variations, such as the voltage slope or changes in coupling capacitance. The model is parametrized with impedance measurements and accurately reflects the impedance of an electrical machine up to 40 MHz. Furthermore, the model is used to evaluate different shaft voltage countermeasures.