This paper proposes an "Active Common-noise Canceler (ACC)" that is capable of eliiminating the commonmode voltage produced by a PWM inverter. An emitter follower using complementary transistors and a commonmode transformer are incorporated into the ACC, the design method of which is also presented in detail. A prototype ACC designed and constructed in t h i s paper verifies the viability and effectiveness in a 3.7 k W induction motor drive using an IGBT inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted ECMI. In addition, the ACC can prevent an electric shock on a non-grounded motor frame and can suppress a motor shaft voltage.

Abstmct---This paper proposes an "Active Common-noise Canceler (ACC)" that is capable of eliiminating the commonmode voltage produced by a PWM inverter. An emitter follower using complementary transistors and a commonmode transformer are incorporated into the ACC, the design method of which is also presented in detail. A prototype ACC designed and constructed in t h i s paper verifies the viability and effectiveness in a 3.7 k W induction motor drive using an IGBT inverter. Some experimental results show that the ACC makes significant contributions to reducing a ground current and a conducted ECMI. In addition, the ACC can prevent an electric shock on a non-grounded motor frame and can suppress a motor shaft voltage.

Abstract-This paper presents theoretical and experimental relationships between radiated electromagnetic noises and commonmode 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.Index Terms-Common-mode transformer, electromagnetic interference (EMI), normal-mode filter.

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