Online Evaluation Method of Frequency Support Capability of Battery Energy Storage Systems

Lithium-ion battery energy storage system (BESS) is expected to provide frequency support for low-inertia grid, with its maximum output power determining the effectiveness of the frequency support. However, existing methods for evaluating the frequency support capability (FSC) of BESS barely consider the impact from the battery output power profile, leading to inaccurate real-time evaluation of the FSC. Therefore, this paper first analyzes the principles and output characteristics of BESS in grid frequency control. Then, an online FSC evaluation method for BESS, which considers the battery state and frequency control output profile, is proposed. the evaluation is based on the equivalent circuit model (ECM) of battery, and the online parameter identification and multi-constraints to estimate the peak power of the battery. The maximum output power of the battery under inertial and frequency damping support is estimated by setting different evaluation time according to the inertial and frequency damping output profile characteristics. The online FSC evaluation helps quantify the maximum virtual inertia and frequency damping that BESS can deliver to the grid. Finally, the 18650 lithium-ion battery is tested by the designed dynamic experiment to validate the proposed evaluation methods.