Research On Conducted EMI Of Boost PFC Converter

Boost power factor correction(PFC) converter has been widely used because of its advantage of low input current harmonic and high power factor. In recent years, the measurement, spectra prediction and mitigation of the conducted electromagnetic interference(EMI) of boost PFC converter have been intensively researched. The characteristics of the conducted EMI spectra of the boost PFC converter are dependant on the control methods, operation modes and input/load conditions. This thesis is dedicated to analyze the characteristics of the common-mode(CM) and differential-mode(DM) noises of the boost PFC converter, discuss the design method of the EMI filter, and reveals the characteristics of the conducted EMI spectra of the average-current-controlled and critical conduction mode(CRM) boost PFC converters under operation modes.This thesis includes three parts.The first part(chapter 2) firstly the drain-to-source voltage of the power switch of the boost PFC converter is regarded as voltage source of generating conducted EMI. The conducted EMI propagation paths of the converter are analyzed and the mixed-mode noise is explained. Then, the suppression of the mixed-mode noise by the differential-mode capacitors, which is located before or after the rectifier bridge, is analyzed. The equivalent circuits of the CM and DM noises are derived, and then the transfer voltage gain of the CM and DM noises are given. The insertion voltage gain of the CM and DM filter are analyzed based on the equivalent circuits of the CM and DM noises. The appropriate structure of the EMI filter for the boost PFC converter is discussed, and the parameter design is proposed.The second part(chapter 3) firstly analyzes the operation modes of the average-currentcontrolled boost PFC converter, i.e., all-continuous conducton mode(CCM), part-CCM/discontinuous current mode(DCM) and all-DCM modes, and the input voltage and load conditions for these modes are derived. Then, the drain-to-source voltage of the power switch of the converter is regarded as the voltage source of generating CM and DM noises, and based on the principle of the EMI receiver, short-time Fourier transformation(STFT) is applied to analyze the Peak(PK), Quasi-Peak(QP) and Average(AV) values of the harmonic amplitudes of the voltage source under different operation modes. The working conditions for the worst conducted EMI harmonics are derived, and the EMI filter design for the average-current-controlled boost PFC converter is discussed.The third part(chapter 4) firstly introduces the principle of the critical conduction mode(CRM) boost PFC converter, and the STFT is applied to analyze the time-frequency characteristics of the harmonics of the conducted EMI and the CM and DM noises. Based on the principle of the EMI receiver, the PK, QP and AV values of the conducted EMI of the converter are analyzed, and the relationship between the harmonic amplitudes and the conducted EMI spectra are revealed. The characteristics of the CM and DM noises spectra of the converter are revealled, and the input voltage and load conditions for the worst conducted EMI spectra of the CRM boost PFC converter are derived. The EMI filter of the converter can be designed based on the worst spectra to ensure that the conducted EMI of the converter satisfying the standard under all working conditions.