Frequency domain EMI-simulation and resonance analysis of a DCDC-converter

This paper proposes a frequency domain model to predict conducted electromagnetic interferences (EMI) caused by a converter. In the model, the nonlinear and time-variant semiconductor switches of the converter are replaced by voltage sources characterized by measurements during operation of the converter. A vector network analyzer (VNA) measurement method is presented to characterize the disturbance path from the voltage sources to the line impedance stabilization network (LISN). The approach shows that the main resonances of the disturbance voltage at the LISN are caused by the coupling path, which is linear and time-invariant. Based on this knowledge, a frequency domain simulation of the coupling path is performed. The simulation reproduces the measured coupling path very well. Based on the analysis of the electromagnetic potential at selected resonance frequencies, an electrical circuit is designed that accurately describes EMC root-causes of the converter.