Frequency Characteristics of Insertion Loss and Loop Gain of VSCC Feedback Active EMI Filters

With recent increases in the switching frequency in power electronics devices, research on electromagnetic interference (EMI) filters has become crucial in the effort to increase power density. Active electromagnetic interference filters (AEFs) have important application prospects due to their small sizes and high integration capacity. Mastering the frequency characteristics of the AEF insertion loss and loop gain establishes the foundation for optimized device design. In this study, the filtering performance and stability of voltage-sensing current cancellation (VSCC) feedback AEFs were theoretically examined from the perspective of the overall system. The fundamental operation of VSCC feedback AEFs was analyzed, and accurate models for each part of the system over a wide frequency range (1 kHz to 30 MHz) were established. Using these models, loop gain and insertion loss models were derived, and their frequency characteristics were analyzed. Expressions for each segment of insertion loss and characteristic frequency were calculated. The basic circuit was shown to be unstable in both the high- and low-frequency regions. Expressions of the cutoff frequency and stability margin, as well as loop gain compensation methods, were determined. Simulation and experimental results demonstrate the accuracy of the simplified insertion loss model and stability analysis. The findings of this study provide a framework for optimized VSCC AEF designs.