Research On Energy Management Strategy Of Photovoltaic DC Micro Grid Based On Hybrid Energy Storage System

The output power of new energy distributed generation represented by photovoltaic power generation has fluctuations,which poses a threat to the safe and stable operation of the power grid.The use of energy storage devices in the micro grid can effectively stabilize power fluctuations.In this paper,the energy management strategy of photovoltaic DC micro grid with hybrid energy storage is studied.By analyzing the requirements of micro grid stable operation for hybrid energy storage system,as well as the charging/discharging feactures of energy storage components,a state based on supercapacitor state of charge(SOC)is proposed.The zoning limit management strategy enables the hybrid energy storage system to avoid overcharging and overdischarging of supercapacitors in the micro grid bus voltage stability control and DC micro grid and large grid coordinated control,and maintain the stable operation of the micro grid.Extend battery life.The key research contents and research results are listed as below:(1)For the traditional hybrid energy storage system limit management strategy,the protection of supercapacitor overcharge or over discharge is not considered,and the system may not work properly.This paper proposes a limit management strategy based on supercapacitor SOC partitioning.The time constant of the low-pass filter is dynamically adjusted according to the output characteristics of the supercapacitor in different SOC intervals,so as to avoid overcharging of the supercapacitor when the hybrid energy storage system performs power allocation.The phenomenon of over-discharge keeps the micro-grid stable.(2)Based on the supercapacitor SOC partition limit management strategy,the DC microgrid bus voltage stability control strategy is studied.When the system power fluctuates,the low-pass filtering algorithm is first used to distribute the power to the energy storage system,and then the dual-loop DC/DC converter is controlled by the double closed-loop control mode,so that the hybrid energy storage system maintains the DC bus voltage stability and the system.While the internal power is balanced,the possibility of overcharging and overdischarging of the super capacitor is avoided.The feasibility of the supercapacitor SOC limit management strategy in the application of DC micro-electric bus voltage stability control strategy is verified by building a simulation model.(3)The limit management strategy of supercapacitor state of charge in photovoltaic DC microgrid system is studied,and the hybrid energy storage coordinated control method of photovoltaic DC microgrid in grid-connected and off-grid mode is analyzed.The simulation model is built in Matlab/Simulink,and the seven working modes of grid-connected and off-grid operation are simulated and verified.The experimental results show that under the condition of ensuring power balance,the battery and supercapacitor can be controlled to charge and discharge.Stable operation in off-grid mode and grid-connected mode.(4)The hardware and software design of the photovoltaic DC microgrid system with mixed energy storage was carried out,and an experimental platform was built.The experiment is carried out in the off-network working mode.The results show that compared with the traditional limit management strategy,the limit management strategy of the supercapacitor state of charge can avoid overcharging and overdischarging of supercapacitors and stabilize the microgrid.Run to extend battery life.