Research On Micro-grid PV System Operation And Control

With economic development and social progress, people’s demand for electricity is growing. At present, development of power system faces two major challenges: energy source and operation mode. Over the past few decades, power supply depend on centralized power supply system. However, it is more and more diffcult to meet the requirements for safety and reliability of power supply, because of its high running costs and difficulty. At the same time, power generation resulted in depletion of traditional fossil energy and triggered a series of environmental problems, such as global warming, affected human health. Therefore, using of renewable energy to replace traditional fossil fuels is the main problem. Solar energy is clean and inexhaustible, and it is suitable to distributed generation. Photovoltaic power is really an important part of the new energy development and utilization. The microgrid is a kind of independent distributed generation network. It can overcome many disadvantages of photovoltaic power generation, such as randomness, volatility, and low-density. It can be constructed close to the local load, and long-distance high-voltage or high voltage transmission is not required in the microgrid system, which can reduce line losses, and save construction investment and operating costs. Therefore, it is important to apply PV power generation units in the microgrid. Four aspects were researched in this paper as follows.First, based on the study of the basic principles of photovoltaic cells, equivalent circuit, operating characteristics and mathematical model, the U-P and U-I characteristic curve of photovoltaic cells were analyzed. In order to verify the correctness of the theoretical analysis, the simulation study was completed based on Matlab/Simulink simulation.Second, by studying three different kinds of photovoltaic systems network topology, a general framework for a school dormitory solar photovoltaic microgrid system was proposed. Meanwhile, a practical parameter calculation method was proposed, such as photovoltaic array, batteries. Third, because of the characteristics of randomness and volatility in the solar battery, the principle of maximum power point tracking was researched, and three commonly used method of maximum power point tracking were analyzed. Perturbation and Observation method is further researched. Based on Matlab/Simulink simulation model, the fixed step perturbation and observation method was simulated, and the impacts of parameters on MPPT were analyzed.Finally, by analyzing the microgrid operation mode, combined with microgrid operation control objectives, the AC-DC microgrid photovoltaic topology was proposed. Based on work characteristics in different work mode, processes of switching between grid and off-grid, switching conditions, and conversions of interface inverter control mode were elaborated. Meanwhile, the battery topology which can work in both grid and off-grid was constructed, and the battery energy control strategy in different work mode was proposed.