Synchronously Switched Active EMI Filter

A switch-mode active EMI filter (AEF) synchronized to a boost converter is introduced in this paper, with very low energy storage requirements compared to passive EMI filters and very high efficiency compared to typical AEF circuits with linear amplifiers. The proposed AEF does not use feedback like typical AEF circuits and thus avoids the bandwidth and attenuation limitations imposed by feedback stability. It can also benefit from simple circuitry by directly using the same gate signals as the main boost converter. Moreover, the AEF does not interfere with the closed-loop controller of the dc-dc boost converter that is usually a challenge when designing an passive EMI filter or a feedback-based AEF. We demonstrate the proposed AEF with simulations and hardware prototypes operating at both 150 kHz and 1 MHz, achieving very high fundamental current attenuation with < 0.3% efficiency penalty while filtering the high ac ripple
$R$
= 0.75 of a boost converter. The proposed switch-mode AEF is a very promising approach to (mostly) replace the conventional LC filter and feedback-based AEF for smaller size and high efficiency.