Reactive Power Flexibility Quantification for Battery Energy Storage Systems

The past decade has witnessed a number of voltage collapse events that require more accountable reactive power response capabilities. Battery energy storage systems (BESSs) have superior controllability and dispatchability relative to many other emerging grid assets. Nevertheless, quantifying the aggregate reactive power flexibility of a group of BESSs is still inadequately studied, resulting from the numerical difficulty in finding an accurate characterization of the mapping from the high-dimensional BESS operational space to a low-dimensional aggregate model. This paper proposes a computationally amenable method to quantify the aggregate reactive power flexibility for BESSs. We use a fixed-point (FP) form surrogate model to represent the complex mapping between BESSs and the aggregate model. Although this model is linear in structure, it resembles the application of the FP algorithm in the process of Picard iterations to converge to the actual solution, which reduces modeling errors. The use of the surrogate model results in a relatively simple convex optimization problem to find the aggregate reactive power flexibility. Simulation case studies verify that the proposed work only introduces a modeling error of less than 0.6% while accelerating the computation by two orders of magnitude.