A Novel Virtual Capacitance Enhancement-Based Active EMI Filter for CM Noise Attenuation

During practical applications, the capacitance limitation creates obstacles and demands a big value of common mode (CM) choke for low-frequency noise attenuation. Traditional active electromagnetic interference (EMI) filter also demands big capacitance or the performance of filter is sensitive to the tolerance of used capacitor. To cope with those problems, this article proposes a virtual capacitance enhancement-based active EMI filter (VCE-AEF). By injecting controlled compensation current flowing through small capacitor, active part of VCE-AEF shows characteristics as negative capacitor. Combined with small positive capacitor, total impedance is decreased which means equivalent capacitance is virtually boosted. The performance of VCE-AEF remains stable and is less related with the capacitance of the used positive capacitor. Experimental results show that the noise attenuation achieved by the proposed VCE-AEF with 2.2 nF capacitors is close to the performance with 220 nF Y capacitors during low-frequency range.