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

Hybrid electromagnetic interference (EMI) filter is combined with passive filtering components and active cancellation part. This kind of EMI filter shows good noise attenuation ability and the total size is tiny. But during design procedure of hybrid EMI filter (HEF), passive part and active part are independent and the interaction between those two parts are 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 attenuation capability of CM noise. Together with active cancellation part, the whole filtering system could better block the propagation of CM noise. A prototype of proposed NI-HEF is built. Experimental results show that this new NI-HEF could achieve a dramatic noise attenuation with tiny size and weight.