Median Filters for Switching Noise Mitigation in Oversampled Power Electronics Control Systems

This article addresses switching noise propagation and its suppression in multi-rate control systems, where the inductor current is oversampled, digitally filtered and the control execution is decimated to single(double)-sampled pulse-width modulation (PWM). The operating points where the sampling instants occur near the switching ones are critical for switching noise sensitivity. It is shown that, when the number of the corrupted samples is high with respect to the number of samples used for filtering, typically considered moving average filters (MAFs) bring a detrimental impact. As an alternative, median filter (MED) is proposed. To decouple the ranking within MED from the switching ripple, repetitive ripple removal is added beforehand. Multi-rate PWM control with the proposed feedback filtering outperforms state-of-the-art double-sampled PWM by eliminating the well-known switching noise sensitivity for small and large duty cycles. In addition, noise-sensitive operating point regions that appear with MAF are successfully suppressed.