Suppression of Rotor-Grounding Bearing Currents Based on Matching Stator and Rotor Grounding Impedances

Pulse-width modulation (PWM) inverter drive systems are widely applied in industry for their great speed-control characteristics and performance. However, the common-mode voltage of the inverter induces motor bearing voltage and bearing current, which result in premature bearing failure. In this paper, the influence of stator and rotor grounding impedances on the bearing voltage of the motor is investigated. A comprehensive bearing-current equivalent model circuit is proposed. Based on circuit analysis, the relationship between bearing voltage ratio (BVR) and grounding impedances is derived, showing that bearing voltage varies with the stator grounding impedance on a V-shaped surface. The minimum BVR appears at some specific combinations of the stator and rotor grounding impedance. Based on this, a method of suppression of rotor-grounding bearing currents based on matching the stator and rotor grounding impedances is proposed. The analytical results are verified by experimental results and show that the bearing voltage can be mitigated by matching the grounding impedances in a proper range