Control System Design For Microgridbased On Battery Energy Storage

Since microgrid is easily affected by photovoltaic cells and load fluctuations, energy storage system plays an increasingly important role in microgrid construction. Under this background, this dissertation focus on the control strategy of PV microgrid based on battery energy storage system. The control system is designed based on the strategy above.Photovoltaic array converts solar energy directly into electricity. In this dissertation, the working principle of photovoltaic array is analyzed, and then the mathematical model of photovoltaic cell is built. And then, this dissertation solves the maximum power tracking of photovoltaic array by the use of perturbation and observation method based on the voltage-current and voltage-power characteristic. At last, the simulation is carried out to verify the model and method.The energy storage system is an indispensable part of the microgrid. By controlling the energy storage system, the power emitted by the microgrid can achieve reasonable distribution. The battery is widely applied to the energy storage system because of its advantages of capacity, reliability and maintainability. In the photovoltaic microgrid based on energy storage system, the battery storage system is requred to both absorb energy and release energy. Therefore, bidirectional DC-DC converter is applied to the microgrid with mapping the two-way flows of energy between photovoltaic and battery by analysing the topological structure and working principle. On this basis, the topological structure of microgrid is designed, and a mathmatical model is built by analysising its main circuit, so as to get prepared for designing the control system.Outputing stable voltage and regulating current and power to adapt to the change of load are the control objective of the microgrid. Based on the above control objective, from the point of energy, this dissertation presents a passivity based control on the basis of mathmatical model. This strategy achieves global stability of the system and meets the bounded requirements of the system for the controller. And then, a simulation model for the control strategy is built in Matlab/Simulink to test the control results under different conditions. Simulation results show that the proposed design of the photovoltaic microgrid control system can output stable voltage and track the changes of load and illumination, and ensure the load work normally. Furthermore, the control system designed in this dissertation is better compared with control strategy based on Hamilton theory.