Research On Control Strategy Of 5kW Triple Bidirectional Buck/Boost Converter

Unidirectional or bidirectional DC / DC converters,as the interface equipment between power supply,load,energy storage medium and DC bus,plays an important role in DC microgrid and other systems.If the interface equipment corresponding to different working conditions in the system is designed one by one,it will inevitably increase the system complexity and design cycle.The different equipment operation logic between different manufacturers will increase the difficulty of system debugging and operational risk.Therefore,it is necessary to integrate multiple functions into one device and switch control strategy according to different operating conditions.The thesis takes triple bidirectional Buck / Boost converter as the research object,and the DC / DC switch converter modeling and control theory are used to study the control strategy of the converter used in DC microgrid system under various operating conditions,which has important practical significance.On the basis of expounding the different topological characteristics of bidirectional DC / DC converters,summarizing the control strategies of bidirectional Buck / Boost converters and analyzing its working principles in detail,the mathematical model of the converter is established by using the small signal analysis method,and the rationality of the power devices selected by the existing experimental platform is verified.According to the functional requirements of the converter for load power supply or balancing system power,its working modes are divided into three types: Buck mode,Boost mode and charge-discharge mode.Using the control theory of switch converter,the control strategies under the three modes are studied respectively.In charge and discharge mode,the bus voltage threshold control is used as the outer voltage loop and the PI regulator is used as the inner current loop to realize the power balance of the system.In Buck and Boost mode,the voltage and current double closed-loop control strategy is adopted to realize the constant voltage output of the converter,but the traditional closed-loop control under wide range disturbance has the problem that the output voltage fluctuation is more than 5%,and reducing the output voltage overshoot will lead to the increase of the regulation time.Therefore,based on the traditional feedback control,the model predictive pre-compensation control strategy is adopted to optimize the dynamic response performance of the converter.Aiming at the problem that the design of model prediction algorithm in model predictive pre-compensation control strategy is more complex and there are many parameters to be set,an improved model predictive pre-compensation control strategy is proposed by combining finite set model prediction with continuous set model prediction algorithm.By model prediction online adjusts the voltage setting value of feedback control,improves dynamic response performance of the converter simplifies the design difficulty and reduces the parameters to be set.In order to verify the feasibility of the control strategies adopted in different working modes and the correctness of the proposed control strategies,MATLAB / Simulink simulation and experiment platform are used to study the three modes.The simulation and experimental results show the feasibility of the control strategy and the correctness of the proposed control strategy.