Research On Bus Voltage Control Strategies Of DC Microgrid

With the increasing problems of fossil energy shortage and ecological pollution,low-carbon and environmentally friendly distributed power generation technologies are gaining widespread attention,and microgrids consisting of wind power,photovoltaic and other renewable energy generation systems and energy storage systems to supply power directly to consumers have become a new trend in the development of power systems.DC microgrids have become a hot topic of research due to their simple topology and the absence of reactive power,frequency and phase.However,DC microgrids suffer from the same low inertia and weak damping problems as AC microgrids,and sudden changes in power output or load power in DC microgrids can cause DC bus voltage fluctuations and affect the normal operation of the system.This paper therefore addresses this problem by conducting a comprehensive study of bus voltage control in DC microgrids and proposing new control strategies.The main work and conclusions of this paper are as follows:(1)The structure and bus voltage control strategies of a typical DC microgrid system are studied.Firstly,the DC microgrid system is simplified according to the roles of different component units,and an equivalent model of DC microgrid consisting of energy storage unit,constant current source and load unit is obtained.Then the mathematical model and operating principle of the energy storage unit are explored and different DC bus voltage control strategies are derived in detail.Finally,a simulation model is built in MATLAB/Simulink to verify and analyse the dynamic performance of the DC bus voltage under different control strategies.(2)Due to the lack of inertia and damping in the DC microgrid,the DC bus voltage fluctuates greatly after receiving disturbances and the dynamic performance is poor.To address this problem,this paper proposes a parameter adaptive virtual capacitor control strategy by combining the capacitor charging and discharging principles.The strategy is able to respond to changes in the DC bus voltage and modify the controller parameters in real time according to the system state,improving the dynamic performance of the DC bus voltage.The parameters of the adaptive control are also designed based on dynamic performance and small signal stability analysis.Finally,the effectiveness of the parameters adaptive virtual capacitor control is verified by simulation.(3)To address the problem that the bus voltage under virtual capacitor control still has sudden changes,this paper improves the virtual capacitor control strategy by connecting the series lead compensation link,and analyzes the dynamic performance of the bus voltage under different series connection methods by comparing the step response of the small signal model,and determines the optimal control method.The parameters of the lead compensation link are also designed in conjunction with the small signal stability analysis.Finally,the effectiveness of the improved virtual capacitor control strategy and the correctness of the theoretical analysis are verified by simulation.