Research On Full-Bridge Push-Pull Bidirectional DC-DC Converter Based On Hybrid Control Strategy

In the face of global climate change,our country is actively implementing countermeasures.’Carbon Peak’ and ’Carbon Neutrality’ were also included in the government work report for the first time in 2021,which aroused widespread public concern.Using clean new energy to replace fossil energy,transforming the energy structure,and reducing carbon emissions from the source are the ways to reduce carbon emissions.In the new energy storage system,the bidirectional DC-DC converter can realize the energy transfer between the energy storage element and the external power system,avoiding energy waste,and has good practical application significance.In this paper,a lithium battery charging and discharging system is used as an application scenario,a full-bridge push-pull bidirectional DC-DC converter prototype is developed and its hybrid control strategy is studied,and the feasibility of the prototype and the control strategy design is verified through simulation and experiment.The main content of the paper is as follows:Firstly,the topological structure of common bidirectional DC-DC converters is compared and analyzed.In view of the application requirements of low voltage and high current,the fullbridge push-pull bidirectional DC-DC converter is selected as the research object.By analyzing the working timing diagrams of charging mode and discharging mode,the full-bridge push-pull bidirectional DC-DC converter is modeled,and the transfer function of input voltage and output voltage is derived.In order to reduce the loss of converter switching devices,synchronous rectification technology is adopted.Secondly,the working principles of the proportional integral controller,quasi-proportional resonance,and proportional feedforward controller are studied in detail,and a simulation model is built based on MATLAB/Simulink.In order to improve the dynamic response speed of the system,it is proposed to use a PI and quasi-PR hybrid controller in the charging mode,and a PI and PFF hybrid controller in the discharging mode.The simulation results show that adding a quasi-proportional resonant controller based on the PI controller can improve the voltage waveform on the high voltage side of the transformer,and improve the system transmission efficiency and system stability.Compared with the PI voltage and current double closed-loop controller,the dynamic response time of the PI and quasi-PR hybrid controller is shortened from 12.15 ms to 2.9ms,and the dynamic response time of the PI and PFF hybrid controller is shortened from 8.5ms to 5.1ms.Finally,the prototype software and hardware are designed,including the parameter calculation and selection of power components,the design of the drive circuit and sampling circuit of the control loop,as well as the program flow and code writing.Based on the above analysis,an experimental prototype with a charging mode rated power of 2.1k W and a discharge mode rated power of 1.65 k W was made,and the prototype was tested to verify the feasibility of the prototype design.Experimental results show that the prototype designed in this paper can achieve a constant output voltage of 14 V in charging mode and a constant output of 380 V in discharge mode.At the same time,in order to avoid excessive discharge of the lithium battery,the prototype has a two-way switching function of power flow,which can automatically select the working mode according to the voltage of the lithium battery to achieve two-way energy flow.