AC motor transients and EMI emission analysis in the ASD by parasitic resonance effects identification

Investigation of common mode (CM) electromagnetic interference (EMI) currents in an AC motor fed by the pulse width modulated (PWM) voltage converter requires a model of the motor that take into account parasitic capacitances existing in the motor windings. Presented CM transfer impedance analysis method shows that the motor voltage transient is strongly related to the resonance effects observed on the windings CM impedance. The wide frequency CM impedance characteristics analysis allows to identify and determine resonance effects which are the primary reasons for voltage ringing phenomena. The paper presents a circuit modelling method of the AC motor windings parasitic capacitances, which allows to take into account the change of the winding to ground capacitance for different frequency ranges in the conducted frequency range. The proposed circuit model and its parameter identification method make possible more accurate CM currents modelling in the AC motor windings fed by the converter.