A Constrained Monotonic Charging/Discharging Strategy for Optimal Capacity of Battery Energy Storage Supporting Wind Farms

A novel monotonic strategy following a consistent charging/discharging direction for each individual battery connected in parallel to form a large-scale battery energy storage system (BESS) is proposed in this paper. The BESS is coordinated with a large wind farm to smooth out the intermittent nature of the farm's output fed to an electricity grid. The strategy is used to optimize the capacity of each battery reducing the system's capital cost. The strategy also prolongs the battery's lifetime and consequently minimizes the system's operating cost. It is shown that the optimal capacity of the battery decreases as their number increases. Moreover, the optimal capacity of the BESS tends to some positive limit as the number of batteries approaches infinity. A rigorous proof of the mathematical theory underlying the proposed strategy and associated optimization are given in the paper. The effectiveness of the strategy is confirmed with data analysis taken from an actual wind farm. The strategy is generic enough to be applicable to other intermittent generation sources such as solar PV farms.