N-Conductor Passive Circuit Modeling for Power Converter Current Prediction and EMI aspect

This paper proposes a method to study the impact of passive circuits such as filters, loads, and board layout on conducted electromagnetic emissions. The method is dedicated to power converters with N active conductors and a ground conductor, followed by passive circuits. A sophisticated use of impedance matrices allows high frequency current prediction. The power system is divided into functional circuits called blocks. Each passive block is modeled by an impedance matrix. A fast matrix calculation permits association of those matrices to obtain a compact model represented by an impedance matrix. Knowing the converter output voltages and the resulting impedance matrix, currents are calculated to study the influence of each passive block on high frequency current spectrum, and so the EMI (electromagnetic interference). This will help for filter and board layout design for a given load. After presenting the general use of the method, the validation is performed on a differential Class-D audio amplifier used in cell phone applications. The practical application on a two-active conductor system validates the method up to 110 MHz.