Spectrum Analysis for EMI Produced by Voltage-Source PWM Inverters

This paper discusses a distributed constant circuit model of power cables for representing high-frequency oscillatory currents, and evaluates electromagnetic interference (EMI) generated by a PWM inverter-fed induction motor drive system. While the lumped constant circuit model which has already been proposed by the authors has only one resonant frequency, the distributed model proposed here can simulate plural resonant phenomena existing in a high frequency range over the first resonant frequency. Frequency characteristics of both common-mode and normal-mode currents are analyzed by using a circuit simulator with the distributed model. As a result, it is shown experimentally and theoretically that the resonant phenomena in the high frequency range are originated from behavior of the power cables as the distributed constant circuit, and that the common-mode transformer (CMT) and the normal-mode filters (NMF's) can damp the resonances.