Equivalent Parallel Capacitance Cancellation for Improving the Characteristics of CM Filters Using Negative Impedance Converter

In this paper, we propose an approach to cancel the equivalent parallel capacitance (EPC) of CM choke with negative capacitance, generated by negative impedance converter (NIC). With the CM choke equivalent circuit, the EPC of CM choke windings are first accurately calculated by testing its impedance using impedance analyzer. The operating principle of NIC is then analyzed and the negative capacitance is realized. Finally, the EPC cancellation is realized through the negative capacitance in parallel with one of the CM choke windings. The cancellation is verified by network analyzer and EMI measurement. Experimental results show that the proposed technique can effectively reduce the effects of EPC and significantly improve CM filter's high frequency attenuation performance.