With the increasing requirement of power density of power electronic converters, it is of great importance to design the electromagnetic interference (EMI) filter to meet electromagnetic compatibility (EMC) standards, meanwhile featuring small size. CL/LC/CLC are the three commonly used topologies. Traditionally, the selection of the topology is determined by the mismatch of noise source impedance and load impedance, ignoring its mismatch with filter components impedance. Therefore, it is still not clear how to accurately select and design the EMI filter. In order to solve this problem, the concept of capacitance allocation coefficient is first introduced in this article to treat the CL/LC/CLC three different topologies with a uniform form, i.e., capacitor-inductor-capacitor (CLC) structure. The unified expression for the insertion loss (IL) of CL/LC/CLC EMI filter is then deduced. From the perspective of achieving maximum IL, an optimal allocation method of the CLC filter capacitance under different noise source impedance is elaborately studied which can quantitatively optimize the topology selection and parameter design to reduce the filter volume. Finally, a corresponding design method of EMI filter is proposed and an EMI filter is designed for a converter based on the proposed method. Simulation and experimental results verify the effectiveness of the proposed method.

The optimal design of electromagnetic interference (EMI) filters relies on accurate characterization of noise source impedance. The conventional insertion loss method involves integrating two distinct passive two-port networks between the linear impedance stabilization network (LISN) and the equipment under test (EUT). The utilization of the insertion loss to formulate a system of binary quadratic equations concerning the real and imaginary components of the impedance of the noise source enables the precise extraction of the magnitude and phase of the noise source impedance in theory. However, inherent inaccuracies in the insertion loss method during extraction can compromise impedance accuracy or even cause extraction failure. This work employs a series inductance method to overcome these limitations. Exact analytical expressions are derived for the magnitude and phase of the noise source impedance. Subsequently, the application scope of the series insertion loss method is analyzed, and the impact of insertion loss measurement error on noise source impedance extraction accuracy is quantified. Requirements for improving extraction accuracy are discussed, and method optimization strategies are proposed. The permissible range of insertion loss error ensuring a solution exists is deduced. Finally, simulation and experimental results validate the proposed approach in a buck converter.

This paper presents a systematic investigation into performance optimization and bandwidth extension strategies for feedforward current-sensing current-compensation (FF-CSCC) active EMI filters (AEF). An equivalent circuit model is developed to characterize the FF-CSCC, enabling derivation of optimal filtering conditions through frequency response analysis and impedance equivalence evaluation against passive filters of identical capacitance. To overcome the inherent bandwidth limitations of conventional designs, a novel compensation methodology coupled with a systematic design framework is proposed for effective frequency band extension. Through sensitivity analysis, key design parameters governing insertion loss characteristics and operational bandwidth limitations are identified. Practical implementation challenges, including parasitic effects in injection capacitors, are addressed through experimental validation on a buck converter. Experimental results demonstrate an average noise attenuation enhancement of 20 dB below 10 MH compared to passive filters, conclusively validating both theoretical efficacy and feasibility of the proposed approach.

The precise in-circuit impedance extraction in a switched-mode power supply (SMPS) is essential for the optimal design of electromagnetic interference (EMI) filters. The design of EMI filter parameters based on in-circuit impedance has already been widely investigated in the literature, but the variation characteristics of the in-circuit impedance for an SMPS is still a research gap and needs further study. In this article, based on the concept of the inductive coupling approach, a novel method for in-circuit impedance modeling is proposed. Subsequently, an accurate in-circuit impedance modeling is derived, which indicates that the in-circuit impedance for the SMPS is related to the external impedance, the modal impedance under different switching modes, and the proportion of each switching mode. Based on the derived model, the variation characteristics of the in-circuit impedance are revealed, which can provide valuable guidance for the design of EMI suppression measures. Finally, the simulation results show good agreement with the calculated results. Experimental verification further indicates that the model accurately characterizes the impedance of the switching power supply across the range of 10 kHz to 30 MHz, with amplitude deviation within 3 dB and phase deviation below 6 degrees. This work provides a quantitative foundation for designing electromagnetic interference suppression strategies, enabling more precise filter optimization over a broad frequency range.