Research On Control Strategy Of Four-switch Buck-boost Converter With Pseudo Continuous Conduction Mode

With the widely application of new energy generation and distributed power system,the higher power density and efficiency are needed.Among the current converter topologies,four-switch buck-boost（FSBB）converter has the advantages of symmetrical structure,the same polarity between input and output,voltage rising and falling both directions,low voltage stress of switch,few passive components and flexible control,which is widely used in various fields.It is difficult to realize zero voltage switching of all switches under most control strategies of FSBB converter.It also causes large switching loss and electromagnetic interference,which is harmful to the high frequency and miniaturization.The negative inductor current can realize all switches ZVS,but it causing part of the power to return to the input and increasing its peak and effective value because the waveform of inductor current decreases under light load.By working in pseudo continuous conduction mode（PCCM）,the negative current and the power reflow can be limited,which improves the converter efficiency.In this paper,the working principle of FSBB converter controlled by PCCM is studied,the ZVS constraint conditions of the four switches are analyzed,and the influence of circuit parameter changes on their ZVS range is compared.In order to achieve all switches ZVS under different conditions,three limiting boundaries need to be met.This paper also studies the relationship between the peak,effective value and the duration of the circuit state.The peak and effective value of the inductor current on the three limiting boundaries is the smallest.The minimum peak and effective value waveforms under different conditions are proposed.Based on the above theoretical analysis,this paper proposes the minimum I_rmsmatching control strategy and its implementation scheme.Finally,an experimental prototype with the input voltage of 36～72V,output voltage of 48V and the power of 250W was built to verify above theoretical analysis.The experimental results show that the minimum I_rmsmatching control strategy can achieve the ZVS of all the switches of the FSBB converter under different conditions.At the same time,it follows the minimum peak and effective value control point of inductor current well with high efficiency.