Research On Control And Conducted Emi Suppression Method Of Four-switch Buck-boost Converter

Four-switch buck-boost converter(FSBB)is a DC/DC converter that supports bidirectional voltage step-down and step-up.It has been widely applied in many industrial fields,such as fast chargers for portable equipment,photovoltaic power generation,DC microgrids,consumer electronics,electric vehicles,unmanned aerial vehicles,and so on.The user’s demand for greener,more portable,and high-performance power supplies encourages engineers to pursue higher efficiency,smaller size,and better performance.And it also brings more challenges to the control technology and electromagnetic compatibility design of power supplies.This thesis focuses on the FSBB working in continuous conduction mode(CCM).It makes the following achievements in high-performance control technology and conducted electromagnetic interference(EMI)suppression technology:1.Four four-mode modulation methods are compared,which provides a basis for selecting the modulation strategy of FSBB.For the inductor current of each method,the analytical expressions of average value,RMS value,and ripple value are deduced.The advantages of each method are summarized and compared.A prototype with a 200 V 400W output is produced,and the losses of key components are estimated.Simulation and experiments verify the correctness of the formula derivation.The results show that the efficiency can be improved by 0.2% by the modulation strategy with a lower inductor current ripple.2.A model predictive control(MPC)with the tuning-free cost function is proposed,which provides a new scheme for the multi-mode operation and the smooth mode transitions while reducing the burden of parameter tuning.The method adopts two switching states in each control cycle.It constructs a tuning-free cost function based on the limit of inductor current ripple and duty cycles.As a result,it realizes online decision and smooth transition of FSBB’s operating mode.Analysis shows that the proposed method is insensitive to changes in inductance and resistance parameters.The experiment shows that the settling time of the output voltage is shortened by 21% compared to traditional methods.The light-load efficiency is increased by 3.4%,and the full-load efficiency is increased by 0.4%.3.A selective common mode(CM)noise mitigation(SNM)method is proposed,which utilizes phase-shift modulation to suppress the CM noise of a selected harmonic order.In this thesis,the mathematical model of conducted EMI is deduced,and the noise source and noise characteristics are analyzed.The article points out the mathematical relationship between the CM noise,the duty cycle,and the phase shift angle.Based on the above analysis,this study designs the look-up table(LUT)based phase-shift modulation and provides an offline generating scheme for the LUT.The recommended operating range and implementation details of SNM are also discussed.The experimental results show that SNM can provide 14 dB noise suppression capability at the key frequency point that determines the design of EMI filter.And the volume of CM filter is reduced by 30%.4.An active EMI filter(AEF)based on predictive pulsed compensation(PPC)is proposed and designed,which adopts low-cost and easy-to-implement hardware to reduce the volume of the CM filter.It compensates the CM noise from the power switches by injecting a rectangular wave with adjustable amplitude into the system.This article analyzes the different requirements of FSBB for the rectangular wave in the boost mode and the buck mode.A complete hardware solution is also provided.The experimental results show that the AEF can provide about 10 dB to20 dB noise suppression capability in the frequency range below 3MHz.It reduces the volume of CM filter by 47%.