An Optimized Control For An Isolated Bi-directional Full-bridge DC/DC Converter

In order to reduce the volume of the system, save cost and improve efficiency, the bi-directional DC/DC converter has gained more and more widely used in the battery charging and discharging system, electric vehicle system, uninterrupted power supply system, solar power systems, aviation power systems, renewable energy systems and other occasions.The Dual Active Bridge(DAB) has been given considerable interest in recent years for its ZVS of all devices,bi-directionnal power flow,near- minimum voltage and current stresses of all devices, high power density,high efficiency and small size.International and domestic academics have done a lot of research on the DAB topology and control strategy.However, the research on the optimized closed- loop control is still short of analyzing.The research object of this paper is the dual active bridge converter, when the converter system parameter is uncertain, the key problems are the output under closed- loop control still is robustness and well-performanced in dynamic response. Based on simplified converter model, the average small signal model of the system and its polytopic model is derived, then this paper puts forward a hybrid optimized strategy with parameter optimization and carries out the design of closed-loop controller, and builds a simulation model to prove the validity of the control strategy and superiority, finally completes the implementation of the control system. The main steps are as follows:Firstly,this paper deduced the output voltage, output power, output voltage ripple and other important circuit parameters in the steady-state operation, then analyzes the key problems of the converter design about soft-switching region and the influence of the dead-band on the phase-shifting angle.Through the simplified circuit model, established the average small signal model of the converter, in view of the converter parameter uncertainty problem, deduced the polytopic model of the converter.Then based on the study and research of the theory of Linear Matrix Inequality(LMI),with an LMI formulation of the Linear Q uadratic Regulator(LQR) problem, the optimized closed- loop parameters which satisfying the given constraints is obtained.In order to enhance the dynamic response performance of the system, introduces the output current in control-loop, a hybrid optimized closed-loop control strategy is proposed.According to the system input and output index, designs the circuit parameters of the control system.Sloving the optimal parameters expression by the LMI toolbox to get the paramerters and completes the design of the close-loop controller of the system. Set up the closed- loop control system simulation model of the converter in Matlab. Simulation results show the characteristics of steady-state and dynamic response as mentioned above,and it also proves the superiority of the system dynamic response when deals with the input voltage and load step disturbance at the same time.Finally this paper completes the hardware circuit design of the system based on the FPGA as the main control chip.Using Q uartus II 9.1 platform, the system software modular design is given with the help of schematic design method. The steady state experiment verifies the correctness of the hardware circuit and the feasibility of the software design.