Mechanism of shaft end-to-end voltage appearing in an inverter-driven motor

This paper addresses shaft end-to-end and shaft-to-frame voltages that appear in a 400-V 15-kW induction motor driven by a voltage-source PWM inverter. Although both shaft voltages have been known to be associated to common-mode voltages, this paper demonstrates a shaft end-to-end voltage in the absence of common-mode voltages. Extensive experiments are performed with the motor subjected to differential-mode voltages. Results show that differential-mode voltages applied across motor phases also cause a shaft end-to-end voltage. It is concluded that the combination of differential-mode voltages with high dv/dt and high-frequency motor asymmetry causes a shaft end-to-end voltage. A model of one motor phase is presented to explain the generation of the shaft end-to-end voltage.