Star Point Overvoltage Resonance Effects in Traction Motor Windings Caused by Close-in-Time Inverter Phase Switchings

Abstract

Machine-internal stator winding overvoltages are based on resonance effects caused by interaction of the stepwise voltage changes due to the inverter switching actions and the winding properties, and the parasitic capacitances between stator windings and machine housing. These overvoltages are typically of highest amplitude at the star point of the stator windings inside the machine, and can result in severe insulation damage and failure of the machine. In this paper we propose a simple equivalent circuit model to describe the effect, and provide equations to calculate the maximum insulation stress analytically. We verify the model with measurements on a 1.5MW traction motor, and discuss a circuit simulation of a full drive system which implements the proposed model. The main advantage of the proposed model is its simplicity combined with good accuracy.