Measurement and reduction of EMI radiated by a PWM inverter-fed AC motor drive system

This paper presents theoretical and experimental relationships in between radiated electromagnetic noises and common-mode and normal-mode currents, paying attention to an induction motor drive system fed by a voltage-source PWM inverter. A method of reducing both the currents is proposed, based on an equivalent model taking parasitic stray capacitors inside an induction motor into account. Electromagnetic interference (EMI) radiated by a 3.7 kW induction motor drive system is actually measured, complying with the VDE 0871 Class A [3m]. Experimental results verify that the combination of the already proposed common-mode transformer and the normal-mode filters being proposed in this paper is a practically viable and effective way to reduce the EMI resulting from both the common-mode and normal-mode currents.