Time Domain Analysis of RF Impedances in Fast Switching Power Electronic Systems

In the field of EMC, RF properties of a system under test are usually analyzed in the frequency domain. When measuring RF impedances in common power electronic systems the result depends on the duty cycle of the device due to averaging effects as the sweep time exceeds the switching cycle duration by far. For this reason, this contribution introduces a switching cycle synchronized RF impedance analysis method. The method breaks down the slow measurement into several quick sub-measurements and allows for a characterization of RF impedances as a function of time as well as frequency. The analysis method is validated in an experimental setup on the basis of reference measurements and analytical calculations. Furthermore, first RF impedance measurement results of a simple buck converter obtained with the proposed method are discussed.