Optimal damping of EMI filter input impedance

Input filter damping has long been recognized as critical for avoiding unintended interactions with a switching power converter. This paper investigates a related problem-dynamic interactions between a converter input filter and the source - and develops optimal damping designs that minimize the dipping in the input impedance of a filter seen by the source. Three different damper circuits are studied and for each an analytical model that defines the optimal damping resistance is presented. Performances of these damping methods are compared in terms of achievable damping effects, power dissipation, as well as size and volume of damping capacitors and inductors. A case study is also presented to illustrate the effects of filter input impedance dipping on system stability and the mitigation of such stability problems by filter damping.