Passive common-mode EMI filter adapted to an adjustable-speed AC motor drive

Electromagnetic interference (EMI) is an unavoidable phenomenon occurred in electrical/electronic systems. A PWM inverter; an essential element in adjustable-speed AC motor drive systems, which are widely used in many industrial and/or avionic applications, is a main source to generate conducted noise emissions, especially the common mode (CM). This causes severe parasitic current problems, especially at high frequencies (HF). These restrict power electronic drive´s evolution. To minimize or eliminate this kind of problems, many techniques have been studied and applied. In this paper, insertion of a passive common-mode EMI filter is proposed. This filter is designed by optimizing its elements values by taking into account real impedances of each part of a considered AC motor drive system. This technique is contrarily to commercial EMI filters generally designed by considering internal impedance of disturbance source and load, equal to 50Ω/50Ω, 0.1Ω/100Ω or 100Ω/0.1Ω. These do not represent the real impedances of the considered system, thus employing the latter EMI filter would make EMI minimization less effective. The proposed EMI filter will be optimized to mainly reduce CM currents owing to its most dominant effects in this kind of system. The efficiency of the proposed optimization method using two-port network approach will be deduced by comparing the minimized CM current spectra, in frequency domain, to an applied normative level such as EN55011, DO-160D.