The effects of end part of winding on parasitic capacitances of induction motor fed by PWM inverter

Parasitic capacitances of motor play a very important role in analysis of bearing current of motor caused by PWM supply. In previous papers, parasitic capacitances generally were acquired from two-dimension symmetry model of motor. The effect of stator winding-end on coupling capacitance was ignored. In this paper, mechanism of common-mode voltage was introduced and equivalent circuit of common-mode of motor was proposed. Relationship between parasitic capacitances and bearing voltage was figured out. 2D and 3D Finite-Element model of motor were established based on geometric dimension of motor respectively which includes with winding-end treatment and not. It´s found that length of extended straight part of stator winding and height of squirrel-cage ring are two main factors which can affect C_sr dramatically. Optimized analysis of C_sr based on the two factors was also carried out and optimized group of parameters had been obtained to make C_sr achive the minimum value.