Research On Economic Operation Of Microgrid Based On Stochastic Programming

It is more and more important to improve utilization of renewable energy, when we are faced with the increasingly serious energy and environmental issues. Microgrid, a new thinking to the utilization of renewable energy, can integrate clean energies efficiently, and create a system with the ability of self-management, protection and control. Wind power, photovoltaic and other renewable energy have random, volatility and intermittent characteristics, which bring many problems to the operation after the access to microgrid. Thus, it is urgent that the management and dispatch in both power side and load side should be improved to increase operation economy on the basis of certain power supply reliability.Stochastic programming method is adopted in this paper, where wind power,photovoltaic and uncertainty of loads are seen as random variables, and economic operation optimization models are studied for the microgrid with only electricity load and the CCHP microgrid in islanding and grid-connected modes, and corresponding operating strategy are discussed.Firstly, the economic operation optimization model for the microgrid with only electricity load in islanding and grid-connected modes are established, and operating strategies based on power supply reliability are proposed. In the islanding mode, priority will be given to scheduling power units to assume spinning reserve to meet the power supply reliability, otherwise, means of removing load or renewable energy power should be taken. In the grid-connected mode, when the electricity price of grid is lower than the generation cost of power units in microgrid, electricity purchase should be increased and outputs of micro power units decreased. When the electricity price of grid is higher than the generation cost of power units in microgrid, electricity purchase should be decreased and outputs of micro power units increased. According to real-time price and spinning reserve price, priority will be given to scheduling power units and the grid, but means of removing load or renewable energy power should be taken when necessary.Then, the economic operation optimization model for the CCHP microgrid in in islanding and grid-connected modes are established, and operating strategies based on heating, cooling and power supply reliability are proposed. Micro gas turbine are used a cogeneration unit, arrangements of heating and cooling production are not less than the predictions, and enough spinning reserve are maintained to meet the power supply reliability. In the islanding mode, cogeneration system assumes the primary heating and cooling load, and electric refrigerator could choose the timing to provide some electricity.In the grid-connected mode, when the electricity price of grid is low, electricity purchase should be increased and outputs of cogeneration equipment decreased. And when the electricity price of grid is high, electricity purchase should be decreased and outputs of cogeneration equipment increased.Then, the chance constraints in the model are converted to their corresponding certainty equivalences, the expression of power shortage expectation is inferred based on distribution characters of uncertainties, which includes new energy output fluctuations and load forecast errors.Finally, cases are analyzed on these models above, and corresponding operating plans are given, which includes outputs of scheduling power units in microgrid, outputs of cogeneration equipment, energy trading arrangements, and corresponding management in both power side and load side. Results also validate the rationality and feasibility of the models and strategies proposed, which provides new ideas for the research on economic operation of mocrogrid, with some reference value for subsequent researches.