Improved passive filter configurations for high-frequency conducted EMI in power electronics

Abstract

EMI filter design is critical for power electronics equipment to be in compliance with the EMI/EMC standards. A good filter design realizes effective high frequency attenuation. Such a design is often achieved empirically, with good common sense, and deemed, by and large, as an art rather than a science. It is well known that the filter parasitics are detrimental to its ability to attenuate high frequency noise. In this paper, the critical effects of parasitics, including component self-parasitics and their respective mutual coupling effects, are first identified and their impact to both differential and common mode noise are quantified. Filter design techniques are proposed to mitigate these adverse effects due to self and mutual parasitics. While reduction of certain critical parasitics such as, ESE of filter capacitors and certain mutual couplings can be realized relatively easily in the conventional discrete filter design practice, reduction of the winding capacitance of the common-mode/differential mode inductor can best be implemented in an integrated filter design. Methods of reducing structural parasitics are investigated in this integrated filter design approach and a design technique proposed for canceling the winding capacitance of inductors that results in significant improvement of CM noise attenuation. A unique class of integrated distributed interconnect EMI filter is introduced. Experimental results are provided to substantiate all the claims made in the paper