| Micro-grid is a new energy supply and management technique, which contains distributed generations, energy storage systems and all kinds of loads. Because of its advantages of high energy efficiency, environment friendly and so on, it draws extensive attention. Due to the volatility and randomness of wind and solar energy, how to use the limited capacity of the energy storage system to maintain the balance of supply and load and accomplish the optimal benefits, becomes the important part of micro-grid integrated control and energy management. This article researched on the operation optimization and reliability modeling of battery energy storage system (BESS) in micro-grid. The results are valuable for the application of BESS in micro-grid. The main work is organized as follows:Firstly, taking a micro-grid with wind/photovoltaic/micro-turbine/BESS as a example, the output mathematical models of the component units are established. Based on the unschedulable and random characteristics of wind and solar energy, prediction methods of wind and solar power have been researched. Considering the capacity and charge-discharge constraints of BESS, the mathematical model of BESS is established.Secondly, corresponding to the role of BESS in the micro-grid, the optimal operation model of micro-grid systems is established, based on the dynamic control of BESS. The objective function consists of maximizing the economic benefits, maximizing the reliability, minimizing the power fluctuation of renewable energy, and best meeting the generation schedule of renewable energy. The model meets the power/load balance constraints of micro-grid, output constraints of power supply, and the capacity, charge-discharge, life constraints of BESS. Subsequently, the fuzzy theory and dualistic factor contrast method are utilized to transform the original problem into a single objective optimization problem, so as to obtain the optimal control strategy of BESS considering various factors.Thirdly, considering the fact that dynamic programming can simulate the charge-discharge movement of BESS comfortably and handle the discontinuation and nonlinear constraints problems in the model, dynamic programming is used to solve the multi-objective optimization model. Numerical results show the validity of this method, which can improve the objectives generally. Furthermore, the results can fully reflect the role of BESS.Finally, as the grid-connected BESS is a series system from the reliability angle, the reliability model of BESS is established using the state space method based on analyzing the structure of two-stage grid-connected BESS. Then the reliability indices of BESS and its components can be acquired, which can provide the data reference for the control and allocation of BESS in micro-grid, as well as the reliability evaluation of micro-grid. |
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