Optimal Battery Energy Storage System Control in Microgrid with Renewable Energy Generation

With the wide use of the renewable sources in the generation of power grid, the high variability of the renewable source output leads to voltage instability and potential cost, which imposes significant challenges to the power grid. Battery energy storage has been considered as an effective mechanism to minimize the fluctuation of power flow exchanged with the main grid in a system with renewable energy sources. In this paper, we consider the optimal control of battery energy storage system (BESS) in a microgrid with renewable energy sources. In particular, we aim to minimize a cost function, which is a general convex increasing function of instantaneous power flow from the grid. The increasing convexity of the cost function makes sure that the power flow from the main grid is as flat over time as possible, and thus minimizes the negative impact of renewable energy integration. Through rigorous analysis, we show that the optimal BESS operation policy exhibits a threshold structure, which can potential lead to a simplified control policy. The threshold structure is validated through extensive simulations. Our results demonstrate that the BESS can significantly reduce the fluctuation of power flow exchanged with the main grid. Besides, we also discuss the effect of BESS capacity on the total cost.