A Review of Shaft Voltages and Bearing Currents in EV and HEV Motors

In most mechanical and electrical systems, reliability is paramount. Consumers, users and operators trust that their product will perform properly over its expected lifetime. Electric Vehicles (EVs) and Hybrid-Electric Vehicles (HEVs) are no exception to this statement. One of the most important components to consider when determining the reliability of EVs and HEVs is the electric motor. Within electric motors, many things can cause reduced reliability. This paper will focus on the most important component: the bearings. In this review paper, a general summary of bearing failure methods is provided along with an in-depth analysis of all facets relating to the shaft voltage and bearing current phenomenon with specific discussion relating to EV and HEV motors. Subsequently, this paper will provide a review of several mitigation techniques to render the bearing current failure mode obsolete.