Practical EMI-filter-design procedure for high-power high-frequency SMPS according to MIL-STD 461

The paper presents a very practical EMI-filter design procedure for high-power high-frequency switch-mode power supplies (SMPS), conforming to the military standard MIL-STD 461. The design procedure is based on the knowledge of base-line common-mode (CM), and differential-mode (DM) EMI. Conducted-emission tests are carried out first according to MIL-STD 461. The measuring current probe only is used to separate the total conducted EMI into CM, and DM components, without the need for a special noise separator. The current attenuation of the filter is then simulated by a MATLAB program, using simplified high-frequency equivalent-circuit models for CM- and DM-filter components. Based on the proposed design procedure, a prototype EMI filter has been implemented for a unity-power-factor boost convertor, operating at a switching frequency of 20 kHz and an output power of 4 kW. Practical aspects in the implementation, such as filter-layout considerations and component selection, are discussed. The performance tests were carried out experimentally on the implemented filter according to MIL-STD 461, to verify the validity of the design procedure.