Modeling of Active EMI Filter Based on VSCC Topology and Method for Suppressing Low-Frequency Noise

Abstract

Abstract

A voltage detection current compensation (VSCC) type analog active electromagnetic interference (EMI) filter is proposed to compensate for the performance shortcomings of passive filters in the low-frequency range. Firstly, an equivalent model for the detection, amplification, and compensation functional links was established, and the complete loop transfer function and insertion loss expressions of the filter were derived. Based on this, combined with the noise suppression requirements in the target frequency range of 150 kHz to 10 MHz, the key parameter designs of the second-order RC sampling network, high-speed operational amplifier (AD8009), and RC compensation injection branch were completed, and the stability analysis in the frequency domain verified that the system had sufficient phase margin within the target frequency range. The simulation results show that the insertion loss of the designed filter can reach more than 10 dB in the 150 kHz to 10 MHz frequency range. To verify the engineering effectiveness, this paper uses an AC-DC converter as the test object and builds a conducted EMI test platform. Comparative experiments were conducted on the original noise, only passive filtering, and passive plus active filtering conditions. The results show that after adding the VSCC-type active EMI filter, the measured average-detected noise fulfills the GB/T 9254.1 Class B requirements, with an extra 15–20 dB low-frequency insertion loss compared with passive-only filtering, verifying the correctness and engineering practicability of the theoretical modeling and parameter design method.