Common mode and differential mode characteristics of AC motor for EMC analysis

In Adjustable Speed Drives (ASD), high frequency parasitic currents cause several unexpected problems, such as premature deterioration of motor winding insulation and ball bearings. In order to understand and to mitigate electromagnetic disturbance it is necessary to use a precise model of the PWM inverter, the energy cable and the AC motor. In this paper, an equivalent circuit of the three phase induction motor for high frequencies is presented. The proposed model details separately the common mode and differential mode characteristics of the AC motor. The high-frequency model has been obtained by means of a frequency domain analysis using an experimental setup and a MATLAB model. In order to verify extracted parameters, in-circuit impedance measurements for the AC motor using an Agilent 4294A Impedance Analyzer are done. The Measured results basically verify the extracted data, while the discrepancy between measured results and simulated results is also analysed.