Multitone Measurements for the Characterization of EMI Filters at High Power Levels

This paper outlines the development of an Electromagnetic Interference (EMI) filter measurement system that allows the analysis of Non-Linear Time Invariant (NLTI) and (Non-)Linear Time Variant (NLTV) behavior. CISPR 17 is one of the common standards for the characterization of EMI filters. CISPR 17 provides the guidelines to measure the performance of filters with small signals and a 50/50 Ω source/load configuration as well as an approximate worst case scenario. The performance of EMI filters is evaluated with the Insertion Loss (IL) curves. Such measurement is not representative of in-situ performance of the filter, as it does not evaluate filters under in-situ conditions which may display NLTV effects. During this study, high power levels are used when evaluating an EMI filter to approximate in situ behavior. The filter components may change characteristics over time due to wear, temperature, and non-linear effects like saturation. These changes manifest in a change in filter performance, observable through the IL curves, which can be considered NLTV behavior. Non-linear behavior due to the high voltage applied was observed, in addition to LTV behavior after increasing the filter’s temperature.