Research On Control Technology Of High-Efficiency Four-Switch Buck-Boost Converter

With the rapid development of new energy,aerospace,communication power supply and other industries and fields,high-efficiency front-end DC-DC converters that are suitable for wide-range input voltage changes and can achieve buck-boost functions have received widespread attention.Among the front-end DC-DC converters,Four-Switch Buck-Boost(FSBB)has been focused by more and more researchers due to its superior performance.This article will focus on the control scheme for FSBB converter.Most of the traditional control strategies of FSBB converter are based on the hard-switching scheme.Under the current development trend of high frequency,high efficiency and high power density,the power loss caused by the hard switching of the power switches limit the improvement of efficiency.Although some literatures have proposed soft switching control strategies,most of them are too complex,or need to add complicated auxiliary circuits to realize the Zero Voltage Switching(ZVS)turn-on.This article aimed to the realization of the high efficiency of FSBB,and proposed relevant soft-switching control scheme on the basis of the unified“four-segment inductor current” modulation.This article firstly focused on the key wavefroms under the four-segment inductor current waveform modulation method.Different from other literatures,here the dead time and the parasitic parameters have been considered.Based on the waveforms,an constraint for the selection of switching dead time have been proposed.Besides,the relationship of the phase-shift-ratio,the power level and the ZVS operating range is analyzed based on the porposed dead-time selection constraints.Then,the necessary and sufficient conditions to realize ZVS turn-on are proposed.Subsequently,the relationship between the phase-shift-ratio and the inductor current ripple was analyzed.It is clear that the inductor current ripple can be reduced by controlling the phase shift ratio,so as to reduce the loss and improve the efficiency of the converter.Finally,by considering the proposed necessary and sufficient conditions to realize the ZVS,as well as the influence of the phase-shift-ratio on the inductor current ripple,a control method is proposed in order to reduce the inductor current ripple.This control method can dynamicly seek the optimized operating point,where the converter can still work in the soft-switching status,and with a minimized current ripple.This is verified by both the simulation and experimental results.