Hierarchical Coordinated Control Strategy for Enhanced Performance of Energy Storage System in Secondary Frequency Regulation

This paper presents a hierarchical coordinated con-trol strategy designed to enhance the overall performance of the energy storage system (ESS) in secondary frequency regulation (SFR). The strategy includes three layers: the system layer, the ESS operation layer, and the coordination control layer. In the system layer, a detailed frequency response model of the multi-area interconnected system is developed. The intrinsic mech-anisms of timing, depth, and the effect of ESS and conventional generating unit (CGU) in SFR are revealed through the sen-sitivity analysis of the power allocation factor. Furthermore, a sensitivity-based adaptive power allocation strategy for ESS and CGU is proposed, which improves the SFR effect while reducing the ESS power and maintaining the state of charge (SOC). In the ESS operation layer, the ESS is divided into two components for integration, employing a monotonic charge-discharge strategy to reduce lifetime degradation caused by frequent charging and discharging, thereby enhancing operational efficiency. In the coordination control layer, considering the power prediction and the ESS operating state, a SOC optimization strategy based on the double-input fuzzy control (DIFC) is proposed. It further dynamically corrects the power allocation factor based on fuzzy rules, optimizing the SOC level to ensure the bidirectional SFR capability of ESS under all conditions. The case studies validate the overall SFR performance of the proposed strategy with different scenarios.