A Hybrid EMI Filter Incorporating Active Y-Capacitor for Common-Mode Noise Mitigation

With the increase in switching speed and power density, the electromagnetic interference (EMI) issues of power converters become more and more serious. Although passive EMI filters (PEFs) have been widely used in engineering fields due to their effectiveness, their bulky components, such as chokes and X-capacitors, hinder the enhancement of power density of power converters. Existing hybrid EMI filters (HEFs) is to combine active EMI filters (AEFs) and PEFs for reducing the wide frequency-band EMI noise in power converters. However, due to the gain-bandwidth product of AEF and the parasitic parameters in PEFs, the existing HEFs also face a big challenge to reduce high-frequency EMI noise and also have bulky volume. Therefore, in this article, an HEF incorporating active Y-capacitor (AY-HEF) is proposed for effectively mitigating common-mode (CM) noise in the wide frequency band. The proposed AY-HEF can effectively extend the upper cutoff frequency of AEF and achieve 15 dB attenuation at 30 MHz. Taking a synchronous buck converter as an example, the experimental results validate the effectiveness of the proposed AY-HEF, there is 10-30 dB CM noise reduction across the frequency range from 150 kHz to 30 MHz, and the volume of HEF is reduced by 76% comparing PEF. Therefore, this article provides a new and compact HEF topology for power converters, which is needed to achieve high power density.