Research On ZVS Control Strategies For Four-Switch Buck-Boost Converter

With rapid development of power electronic technology in recent years,non-isolated DC-DC converters have been widely used in many fields such as telecommunication distributed power supply system,photovoltaic power system,electric vehicle and so on,where the power density and efficiency are increasingly demanded.Meanwhile,the popularity of soft-switching technic brings the possibility for high density and high efficiency DC-DC converter.Among many non-isolated buck-boost topologies,four-switch buck-boost(FSBB)has become one of the research hotpots in Buck-Boost DC-DC application for it features low voltage and current stress for devices.However,multiple degrees of control freedom increase the complexity and challenges in the control strategies for FSBB converter.First,targeted in conduction loss,this paper proposed a minimum RMS of inductor current zero-voltage-switching(ZVS)fixed frequency control for FSBB converter.Quadrilateral inductor current modulation is adopted to achieve ZVS for whole operation.The four control time intervals of inductor are optimally selected to minimize the RMS value of in ductor current.The proposed closed-loop control system does not require load current sampling,simplifying the control circuits.In order to verily the theoretical analysis,a 300W prototype is built.The load and input voltage transient test are conducted to test the characteristic of the proposed minimum RMS inductor current control strategy without load current sampling.The realized fixed frequency minimum RMS inductor control reduces the conduction loss,but in the wide input and output voltages application,the minimum RMS algorithm needs 3-D look-up table,which is difficult to implemented in the general-purpose micro-controller for its limited memory resource.To solve this problem,this paper proposed a unified single variable ZVS control for FSBB converter.It not only maintains low RMS value of inductor current but also features less computation and doesn't need 3-D look-up table,dramatically mitigating the memory stress for digital controller.Therefore,a high frequency ZVS control for FSBB can be easily implemented in a lower cost MCU.A 300W prototype is built up to verify the proposed control algoritlhm.The results show that the proposed unified single simplified variable ZVS control has narrow frequency ranges and reduced real-time computation without inreasing conduction loss.