Research On Control Strategy Of DC Micro Grid Hybrid Energy Storage System Based On Model Predictive Control

The Hybrid Energy Storage System(HESS)consisted of the battery and the super capacitor has the advantages of high power density and high energy density to effectively maintain bus voltage stability when the micro grid bus power fluctuates.Hybrid energy storage system control strategy usually adopts double closed-loop control algorithm based on PI control.In traditional double closed-loop control,Proportional Integral(PI)is based on the measured value of lag adjustment,and there is a problem of slow dynamic response,energy storage converter cannot quickly respond to changes the bus voltage.In this paper,a hybrid energy storage system control strategy based on Model Predictive Control(MPC)is proposed.MPC is based on the advance adjustment of the state model,it can solve the problem of slow response of the inner loop in the traditional double closed loop,thus reducing the recovery time of the bus voltage when the grid power fluctuates,and enhancing the stability of the micro grid operation.The main research contents of this paper are as follows:Explain the basic structure of DC microgrid and compare the common forms of HESS connecting to the DC bus;furthermore,this thesis selects the topology of HESS used in this paper and makes a research on the charging and discharging characteristics of the battery and super capacitor in the system.The problem of slow dynamic response in traditional double closed-loop HESS control strategy is analyzed.Compare the working principle of the traditional PI control and MPC,and analyze the factors that affect the dynamic response speed of the two control methods.Aiming at the problem that the prediction error of MPC affects the stability of the system,the multi-step prediction method is used to improve the traditional MPC.In this paper,a double closed-loop optimal control strategy for HESS is proposed.The improved MPC is used as the inner loop control of the double closed-loop to improve the dynamic response speed of the system.The double closed-loop optimal control strategy of HESS is designed.The simulation model is built in MATLAB/Simulink,and the traditional double closed-loop control and improved control strategy are applied to the hybrid energy storage system to stabilize the power fluctuation of the DC bus of the microgrid.The simulation results show that the improved control strategy can effectively reduce the time when the bus voltage is restored to the rated value when the bus voltage is abrupt,which improves the stability of the microgrid.The experimental platform of the hybrid energy storage system is built to carry out the experiment of the hybrid energy storage system to stabilize the power fluctuation of the DC bus.The results show that compared with the traditional double closed-loop control,the hybrid energy storage system control strategy based on the model predictive control method can improve the dynamic response speed of the hybrid energy storage system,and reduce the recovery time of the voltage when the bus voltage is abrupt by 65%.The effectiveness of the MPC-based hybrid energy storage system control strategy proves that the proposed hybrid energy storage system control strategy has certain theoretical significance and practical application value.