A New Negative Inductance-Based Hybrid EMI Filter With Enhanced CM Noise Attenuation Ability

A hybrid electromagnetic interference (EMI) filter is combined with passive filtering components and an active cancellation part. This kind of EMI filter shows good noise attenuation ability, and the total size is tiny. However, during the design procedure of the hybrid EMI filter (HEF), the passive part and the active part are independent, and the interaction between those two parts is not well considered. To cope with this problem, this letter proposes a new negative inductance-based HEF (NI-HEF). By constructing a negative inductance-based sensing structure, the sensing transformer could not only sense the common mode (CM) current but also boost the impedance of primary windings, which, in turn, helps to increase the attenuation capability of CM noise. Together with the active cancellation part, the whole filtering system could better block the propagation of CM noise. A prototype of the proposed NI-HEF has been built. Experimental results show that this new NI-HEF could achieve dramatic noise attenuation with a tiny size and weight.