Control Strategy For Hybrid Energy Storage System To Maintain Bus Voltage Stability In Microgrid

Hybrid Energy Storage System(HESS),which is composed of lithium ion batteries and supercapacitors,takes into account the advantages of high power density and high Energy density,and can effectively maintain the stability of bus voltage when the power of the microgrid fluctuates.With the development of a new generation of power systems,the control accuracy of HESS control strategy in microgrid is also required to be higher.In this paper,a hybrid energy storage system Control strategy based on Model Predictive Control(MPC)is researched and designed,so that the hybrid energy storage system can quickly adjust the bus voltage,improve the Control accuracy and maintain the bus voltage stability of the microgrid system when the power of the DC microgrid fluctuates.First,the basic structure of the HESS-containing DC microgrid is described,the working principle of the lithium ion battery and the supercapacitor in the system is analyzed,the equivalent model is established,and the charge-discharge characteristics of the two types of energy storage components are studied.The extension structure of HESS is selected according to its charge and discharge characteristics and the control objective in this paper.Second,the double closed loop PI control strategy commonly used in HESS is studied.According to the principle of bidirectional DC-DC converter,the mathematical model is built,and based on the mathematical model,the design of double closed-loop PI control strategy is completed,and the control performance is simulated.The simulation results show that the control accuracy of double closed-loop PI control needs to be further optimized.Thirdly,the control strategy of HESS is optimized.MPC control algorithm is proposed.Compared with PI control,the control accuracy of MPC control algorithm is significantly improved.However,the prediction error of MPC algorithm will affect the control accuracy of the system.Aiming at this problem,a double closed-loop improved MPC optimization control strategy was proposed.The prediction model of outer loop voltage and inner loop current was built respectively to form a double closed-loop structure,and the change rate of controlled quantity was limited in the objective function to improve the control accuracy of MPC algorithm.Fourth,the overall control strategy of HESS is designed based on the improved strategy,and the system model is built in Matlab/Simulink.The simulation results show that the improved control strategy can effectively reduce the maximum overshot of bus voltage recovery,improve the control precision,and thus improve the voltage quality of microgrid operation.Finally,the experimental platform of the hybrid energy storage system was built to conduct the experiment of HESS suppressing the power fluctuation of the DC bus.The experimental results show that,compared with HESS based on double closed-loop PI control method,the overshoot is reduced by 70%,and the control precision is significantly improved.Compared with the HESS control strategy based on MPC control method,the overshoot is further reduced by 37%,and the control precision of the system is further enhanced.Therefore,the proposed control strategy can effectively reduce the maximum overshoot of the bus voltage recovery,improve the control accuracy of the hybrid energy storage system,reduce the influence of power fluctuations on the microgrid,improve the voltage quality of the microgrid,and ensure the efficient and stable operation of the microgrid hybrid energy storage system.