| Energy storage device as an integral part of the microgrid equipment plays an important role to ensure safe and stable operation of the system, to improve power quality and reliability, and to optimize the economic benefits of micro-grid. In this thesis, the hybrid microgrid composed of wind farm, photovoltaic generation and energy storage system; is the research object. The realization of the microgrid security and stability is the goal, and the mechanism of energy storage devices in the micro-grid was researched.First, the various types of energy storage device in microgrid were recommended, and the effect of energy storage device in the microgrid was analyzed. The microgrid energy storage system was classified into distributed storage and centralized storage by the different access of energy storage device. As the Battery energy storage was the research object, a battery equivalent circuit model and charging and discharging circuit was established, the charge and discharge control method of the battery was designed.Secondly, the operation characteristics and control strategy of the microgrid was researched. In the hybrid microgrid composed of wind farm, photovoltaic generation and energy storage system;, photovoltaic cells, direct drive permanent magnet synchronous wind motor and battery energy storage was connected to the grid through the inverter. So three control strategies based on power electronics interface have been researched. They were PQ control, V/F control and Droop control. What’s more, the system-level control strategies of the microgrid have been researched. They were centralized control and peer-to-peer control.Then, in order to construct the microgrid system containing wind power, solar power and energy storage, the two-stage photovoltaic power generation system and the direct-drive permanent magnet synchronous wind power generation system was established. The maximum power point tracking control method of the photovoltaic cell based on the perturbation and observation method of the duty ratio in a the Boost circuit and the maximum wind power tracking control method under optimal tip speed ratio have been devised, achieve the maximum utilization of solar and wind energy. In addition, the grid-connected inverter control strategy using the DC voltage outer loop and the inductor current inner loop was designed, which realized the photovoltaic cells and direct-drive permanent magnet synchronous wind motors connecting to the power generation.Finally, the microgrid system containing distributed energy storage and centralized storage scenery storage, two different topologies, was established. Moreover, the microgrid with centralized storage was designed as master-slave control, and the microgrid with distributed energy storage was designed as peer-to-peer control. Basing on the Matlab/Simulink software simulation, the two different structures of microgrid realized safe and stable operation under network mode and island mode, as well as the smooth switching between the two modes of operation. In the end, the effectiveness and correctness of the control strategy was verified. |
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