A Comprehensive Review of Bearing Current Phenomena in Electric Vehicle Drive Systems

The increasing adoption of electric vehicles (EVs) has brought renewed attention to the reliability and durability of drivetrain components, particularly electric motor bearings. Bearing currents induced by high-frequency voltage potentials from inverter-fed motors have become a significant source of premature bearing failure in electric powertrains. Rolling bearings represent essential elements in electric machines, having a direct influence on their efficiency, operational stability, and lifespan. The rapid expansion of pulse width modulation (PWM) inverter-based drive systems has introduced new electrical stress factors within motors, among which bearing currents have become a critical concern. These parasitic currents can pass through the bearing contacts, causing surface deterioration such as pitting and fluting. Over time, this degradation accelerates wear, diminishes the operational lifetime of the motor, and may ultimately lead to unexpected system failure Current research on bearing current-related degradation primarily focuses on three main aspects: the physical mechanisms responsible for current generation, the key influencing parameters governing these phenomena, and the development of equivalent circuit models to describe current paths through the motor system. This paper presents a comprehensive analysis of the electrical currents passing through bearings used in electric vehicles. The mechanisms of current generation, including common-mode voltage, capacitive coupling, and electromagnetic induction, are examined in depth. Furthermore, the effects of various operating conditions such as motor speed, load, inverter switching frequency, and temperature on the amplitude and frequency of bearing currents are evaluated. The resulting electrical and thermal stresses that accelerate bearing degradation are discussed based on both experimental results and simulation models. Current mitigation strategies, including the use of insulated bearings, grounding techniques, and advanced inverter control methods, are assessed in terms of their effectiveness and limitations. Finally, the paper outlines future research directions aimed at developing integrated design and diagnostic approaches to predict, monitor, and minimize bearing current effects, thereby enhancing the reliability and lifespan of electric vehicle drivetrains.