Research On Control Technology Of DC Microgrid Hybrid Energy Storage System

In recent years,new energy power generation has become one of the research hotspots as an alternative to traditional power generation.Distributed power sources consisting of wind power and photovoltaics are usually connected to a microgrid and then connected to the large grid.The DC microgrid has a better development prospect due to many advantages,such as fewer converters,easier to control and interface with source and loads.The energy storage is an important part of the DC microgrid and plays an important role in suppressing power fluctuations.Compared with the energy storage system of the single medium,the hybrid energy storage composed of super capacitor and battery has been widely used,which can quickly suppress power fluctuations and extend the service life of the battery.The traditional control strategy of the hybrid energy storage system is to use the filtering method to divide the difference between the distributed power and the load power into high and low frequency parts.The high frequency power and the low frequency power are respectively used as the target power of the super capacitor and the battery.In a DC microgrid,most closed-loop controlled load converters can be considered as constant power loads,and the negative impedance characteristics they exhibit may amplify the instability of the system and even cause the entire system to fail.Therefore,it is very necessary to ensure the stability of the system during operation.Therefore,this paper proposes a control strategy for a hybrid energy storage system consisting of the supercapacitor and the battery,and considers the effect of constant power load on system stability.On the basis of the traditional control method,the value of the filter time constant is changed in real time according to the change of the constant power load power to change the energy ratio of the super capacitor and the battery,and the stability of the system is optimized.The Takagi-Sugeno(T-S)fuzzy model is introduced to establish the large-signal model of the DC microgrid,and the Lyapunov function is obtained.According to the Lyapunov stability theorem,the stability domain of the system under different filtering time constants is obtained.Then analyze the influence of the change of the filter time constant on the stability,and select the filter time constant value that satisfies the stability requirement.In order to verify the proposed control strategy,this paper builds a DC microgrid model simulation with hybrid energy storage system in Matlab/Simulink software.A DC microgrid experimental platform with hybrid energy storage system and constant power load is built.And the experimental results verify the effectiveness of the hybrid energy storage system control strategy.The control strategy proposed in this paper can make full use of the high power density of the supercapacitor and the high energy density of the battery,while enabling the system to maintain stability.