Two-Stage Global Optimisation Hybrid Method for Energy Storage Configuration in Distribution Networks

High-penetration photovoltaic (PV) integration into distribution networks often causes operational challenges, including nodal voltage violations and reduced PV absorption capacity. To address these issues, this study presents a two-stage hybrid energy storage system (HESS) optimisation framework that coordinates microgrid operations with the larger distribution network, thereby improving energy storage synergy and collaborative control among microgrids. Initially, a PV utilisation mechanism is developed, along with an HESS model that explicitly considers supply–demand balance constraints. Subsequently, a joint optimisation structure is designed, integrating local microgrid optimisation with overall distribution network management. In the local microgrid optimisation stage, HESS capacities are allocated to minimise overall costs, and the ratio of lithium-ion to hydrogen storage is optimised to maximise renewable energy use. In the global coordination stage, the operation of multiple microgrids within the distribution network is optimised to reduce total system costs and voltage deviations, ensuring balanced and coordinated performance across the entire network. The proposed approach is tested using real data from a typical distribution area in Zhejiang Province, China, combined with a synthesised 33-node system. Simulation results show that the two-stage HESS optimisation significantly improves voltage quality, PV capacity, system flexibility, and overall economic performance.