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 electromagnetic interference. This will help to 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.