MODELING AND OPTIMIZING A PASSIVE EMI FILTER TO ATTENUATE COMMON-MODE CURRENTS AT HIGH FREQUENCY IN A THREE-PHASE ADJUSTABLE-SPEED AC MOTOR DRIVE

This paper proposes a novel optimization approach of a passive electromagnetic interference (EMI) filter using two-port network technique to reduce or minimize common-mode (CM) conducted noise emissions in a three-phase adjustable-speed AC motor drive. This parasitic current is generally generated by a Pulse Width Modulation (PWM) inverter, an essential part in adjustable-speed AC motor drive systems widely used in many industrial and/or avionic applications, and causes severe EMI problems, in particular at high frequencies (HF); this restricts power electronic drive's evolution. The proposed EMI filter is designed by optimizing its elements values by taking into account real impedances of each part of the considered system. This approach is contrary to commercial EMI filters typically designed by considering internal impedance of disturbance source and load, equal to 50 ohm/50 ohm, 0.1 ohm/100 ohm or 100 ohm/0.1 ohm. These do not represent the real impedances of the system; thus employing the latter EMI filter would make EMI minimization less effective. The efficiency of the proposed optimization method will be confirmed by comparing the minimized CM current spectra, in frequency domain, to an applied normative level such as EN55011 or DO-160D standards.