Reliability-driven power system expansion planning incorporating hybrid energy storage and renewable energy under physical attacks

This study proposes a techno-economic power system expansion planning (PSEP) framework that employs a complementary hybrid energy storage system (ESS) strategy to mitigate the adverse impacts of physical attacks. The framework integrates multiple ESS technologies, categorized into long-duration (slow-response) and medium-duration (fast-response) systems, to enhance overall system reliability. While long-duration ESSs offer high energy capacity, they typically lack the response speed required for fast-acting disturbances. In contrast, medium-duration ESSs deliver rapid support but are limited by shorter discharge durations. By leveraging their complementary operational characteristics, the applied hybrid strategy enhances system adaptability under time-varying and evolving threats. The planning model is formulated as a multi-objective optimization problem. The first objective minimizes the total system cost, including investment and operational expenditures, expected energy not supplied (EENS), and reliability-related costs. The second objective maximizes system reliability by minimizing EENS under attack conditions. A physical attack-driven strategy is also introduced to identify and rank the most vulnerable generation units and transmission lines, guiding targeted investment in critical infrastructure. To solve the problem, a multi-objective secretary bird optimization algorithm is applied. The model is validated on the Garver network and the IEEE 30-bus system using various hybrid ESS configurations that combine three long-duration ESSs with eight fast-response ESSs. The results confirm the superior economic and technical performance of hybrid ESS configurations, particularly the combination of pumped hydro energy storage (PHES) and iron–chromium (Fe–Cr) batteries, compared to single-technology ESS solutions. Specifically, the PHES & Fe-Cr configuration achieved total planning cost savings ranging from approximately 9 % to 69.5 % compared to individual ESS technologies. Furthermore, the study reveals that extended overlapping operation periods and increased sharing durations of medium-duration ESSs significantly raise planning costs. Particularly, increasing the sharing period for the fast response of ESSs by 15 min raises the cost of the hybrid ESS by approximately 6.5 % to 44.3 %. Additionally, extending the overlap period by four minutes results in a cost increase of about 2.2 % to 10.5 % for the hybrid ESS.