| V2G technology is a key technology that enables NEVs to participate in the peak and frequency regulation of the grid,and to absorb new energy in large quantities by using NEVs as large-scale distributed energy storage units to interact with the grid.With the rapid development of the country’s new energy industry,the total number of new energy vehicles has been increasing year-on-year.In the face of complex work scenarios and higher power quality requirements,higher demands have been made on V2G vehicle-borne converters,which are key devices for V2G technologies.However,the topology selection and controller design of conventional V2G on-board converters cannot meet the requirements of high power density,high power transmission efficiency,high power quality,and robustness.In this thesis,the Tung column-free PFC bidirectional converter and the CLLC bidirectional resonant converter are selected due to their high power density,high power quality,high power transfer efficiency,etc.and their ability to realize the power interaction well under complex conditions.In,a fractional control strategy for V2G onboard converters is proposed to improve the dynamic response and robustness of the system.The main findings of this thesis are the following.(1)This thesis expounds the background and significance of V2G on-board converter,fractional calculus and fractional control,introduces the topology and structure design of V2G on-board converter and the development status of fractional calculus and fractional control strategy,and summarizes the importance of combining V2G on-board converter with fractional calculus theory and fractional control.(2)In this thesis,the traditional integer order V2G on-board converter cannot accurately describe the actual system in the analysis and modeling,and the mathematical model obtained is not general.Firstly,integrating operator S-αis introduced based on the theory of fractional-order calculus to construct the fractional-order equivalent topology of Totem pole bridless PFC converter and CLLC bidirectional resonant converter.The working modes of the fractional-order system are emphatically analyzed,and the fractional-order equation of state and the energy transfer relations for each mode circuit are listed.(3)Combining the theory of fractional-order calculus with the state space average method and the extended description function method,a fractional-order modeling method suitable for PFC and CLLC bidirectional converters is proposed.The fractional small signal model of the system is derived and the fractional transfer function of the control input to the output is established.Considering the strong coupling between PFC and CLLC,a joint mathematical model of the system is developed.The influence of fractional orderαandβon the amplitude-frequency characteristic curve and stability of the system is analyzed based on MATLAB/Simulink simulation platform.(4)Aiming at the problem that the classical PI control strategy is not effective in the variable working conditions of V2G on-board converter,a double closed-loop fractional PI~λcontrol strategy is proposed for V2G on-board converter.By analyzing the topology structure of V2G on-board converter and establishing the fractional small signal model of V2G on-board converter,this method adopts the voltage-current double closed-loop control structure,and adopts the improved Oustaloup algorithm to approximate fit the fractional integral operator,so as to establish the fractional PI~λcontroller.The optimal control parameters of the system are designed by the fractional transfer function of the system,which is applied to the control of the bus voltage,current,and output voltage and current of the V2G vehicle-mounted converter.Finally,based on the MATLAB/Simulink simulation platform to compare the performance of the fractional-order PI~λcontrol strategy and the classical PI control strategy,it can be concluded that the fractional-order PI~λcontrol strategy has better performance.(5)Finally,the fractional-order PI~λcontrol strategy is tested based on the V2G on-board converter prototype.The experimental results are in good agreement with the theoretical analysis,which proves that the proposed fractional control strategy for V2G on-board converter has good dynamic response,steady-state performance,robustness,and can achieve better bidirectional energy transmission. |
