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

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