Definition and Implementation of an EMI Figure of Merit for Switching Pattern in Power Converters

Power transistors are a source of electromagnetic interference (EMI) during switching due to the high levels of voltage/current transient. Reducing the switching duration can reduce the EMI generation but increases the switching power losses. For this reason, a transistor driving method has to ensure an adequate trade-off between EMI and switching losses. Several driving techniques to reduce the EMI generation have been proposed in the literature. Commonly, a spectrum analysis is used to evaluate their EMI reduction, nevertheless in this paper a more synthetic figure of merit (FOM) is proposed. It is deducted from time-frequency co-spread of both rising and falling edges of switching waveforms. The main interest of FOM is that whatever the waveform, according on Heisenberg-Gabor inequality, it is proved that the lower bound of time-frequency co-spread exists and it is reached when a Gaussian pattern is used. The FOM is validated and implemented by simulation with both theoretical and practical waveforms.