A Research On Inhibition Technology Of Common-Mode EMI In Switch Mode Power System

As the development of power electronics, the switching mode power supply(SMPS) becomes smaller and its working frequency is higher. Therefore, theelectromagnetic interference (EMI) in it is more serious when the components work.Therefore, the electromagnetic compatibility (EMC) in SMPS is drawing moreattention than before. Recently, soft switch is widely implied for its reduction ofswitching losses and promotion of efficiency. The main objective of this paper is toanalysis the EMI in SMPS, research the influence of soft switch, and offer a filteringmethod to exhibit common mode EMI.First, the definition of EMC was introduced, and then the characteristics of EMIin SMPS, and the research status of EMI in SMPS. Starting with three elements ofEMI, the interference sources and coupling paths were discussed. After the highfrequency models of inductor, capacitor and high frequency transformer were founded,the definition and function of line impedance stability network (LISN) wereintroduced. In second part, the definitions of soft switch were introduced, and theworking principle of full bridge zero voltage switch (FBZVS) was analysis. Then theCM coupling path in FBZVS was discussed when the parasitic capacitors of IGBTwere considered. Then, the control and main circuit of FBZVS was designed usingchip UC3875. In the last, to inhibit the CM EMI, this paper proposed a novel EMIfilter combining passive and active filters, in which matching network was introducedin passive filter to reduce the effects of impedance mismatch and feed forward controlwas used in active filter to compensate the CM noise.FBZVS was simulated in Saber, and the conducted interference when full bridgecircuit was working at ZVS condition and hard switch condition were compared. TheCM noise of FBZVS was smaller than that of hard switch at high frequency, but inlow frequency is more or less than hard switch, and differential mode (DM) noise ismuch smaller. The hybrid EMI filer simulated results show that the inhibition to CMnoise is good. Compared with traditional passive EMI filter, it has much advantage insize and weight.