CRM Boost PFC Circuit Conduction EMI Analysis And Suppression Method Research

Active power factor correction techniques have been widely applied in both high-power and low-power ac-dc converters.For hundreds-watt level applications,boost power factor corrector(PFC)operating in continuous current mode(CCM)is widely adopted.The dv/dt on the transistor/MOSFET is the major conducted electromagnetic interference noise source of the converter.For lower power level applications,more and more boost PFCs are designed to operate in critical mode(CRM)or discontinuous current mode(DCM).The characteristics of the conducted EMI spectra of the converters are dependent on the operation and control methods.The characteristics of the conducted EMI spectra of the CRM Boost PFC has been discussed in this paper.Firstly,the peak inductor current,switching frequency of expression,and the corresponding curves in a single switching period are analyzed in this paper.At the same time,the parameters of the boost inductor,switch,output capacitance are analyzed and designed,the components of the application model are selected.A detailed model is derived in this paper to verify the reliability of the theory.Secondly,the noise of the CRM Boost PFC has been given in this paper.In such converters,the dv/dt on the bridge diodes is more severecompared to the CCM Boost PFC,thus becoming the dominating conducted EMI noise source.The conducted EMI propagation of common mode and differential mode are analyzed,so as the mixed-mode noise.Then,suppression of the mixed mode noise by the differential mode capacitor,which has been discussed in the simulation software.Simultaneously,in order to investigate the EMI behavior of the drive circuit of MOSFET,a model of drive voltage signal has been given in this paper.The appropriate structure of the EMI filter is discussed,then the transformer shielding design is proposed.Finally,based on the theoretical and simulation analysis,a prototype of CRM Boost PFC with low power of 100W is built up,then test the output voltage at 220V AC input voltage.The EMI noise of the prototype is tested by R&S EMI receiver ESU26.Testing the EMI spectrum of AC input 0V and 220V and analyzing the EMI noise caused by driving voltage overshoot.Voltage overshoot can be suppressed by adding a capacitor between the control terminals of the DC power supply.Simultaneously verifying the ability of the designed EMI filter to suppress the EMI emission of the prototype.