AC Motor Windings Circuit Model for Common Mode EMI Currents Analysis

Investigation of common mode (CM) currents flowing in an AC motor as a result of a frequency converter´s output excessive voltage stresses, requires a model of the motor that take into account parasitic capacitances existing in the motor windings. 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 converter.