Investigation on capacitive parasitization in PWM inverter-motor drive system

The effects of parasitic capacitances in induction motor system are minor when it is fed from the AC line, but they are obvious when it is powered directly from the PWM inverter. Consequently, many parasitic problems occur, such as EMI and RFI, motor-to-earth leakage current, bearing current, incoming line current distortion, etc. On the basis of the uniform transmission line principle, another equivalent circuit of the PWM inverter-motor drive system is presented, based on which many capacitive parasitic problems mentioned above are analyzed and simulated by means of PSPICE. Other problems such as uneven distribution of the electrical stresses along the winding, the relations between capacitive parasitization and the switching frequency are also analyzed and simulated. All the results are consistent with existing results.