Impedances Identification of DC/DC Converters for Network EMC Analysis

The design of optimal electromagnetic compatibility filters for converters used in electrical networks requires the precise knowledge of input and output terminal impedances. For this reason, the knowledge of the network impedance, including all connected converters, is determined. This paper proposes a study of both the common mode (CM) and the differential mode (DM) impedances of modern embedded networks including cables and several converters. Using a dc network for illustration, we determine the impedance taking into account all operating states of a converter (online or offline operations). Without any restrictions, a theoretical model is developed to express the CM and DM impedances using a switching function and a Fourier series decomposition. An experimental validation has been carried out in a frequency range from a few Hertz up to 80 MHz. Our model has then been used in a simple network, so as to compute the network impedance. Measurements have confirmed the proposed model accuracy.