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 highfrequency 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 MILSTD 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 equivalentcircuit 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 MILSTD 461, to verify the validity of the design procedure.