System Strength Constrained Grid-Forming Energy Storage Planning in Renewable Power Systems

With more inverter-based renewable energy resources replacing synchronous generators, the system strength of modern power networks significantly decreases, which may induce small-signal stability (SS) issues. It is commonly acknowledged that grid-forming (GFM) converter-based energy storage systems (ESSs) enjoy the merits of flexibility and effectiveness in enhancing system strength, but how to simultaneously consider the economic efficiency and system-strength support capability in the planning stage remains unexplored. To bridge the research gap, this paper develops a system strength constrained optimal planning approach of GFM ESSs to achieve a desired level of SS margin. To this end, the influence of GFM ESS power capacities and locations on the system strength is firstly quantified based on the framework of generalized short-circuit ratio. On this basis, system strength constrained optimal placement and sizing of GFM ESSs is formulated into optimization problems with eigenvalue constraints. Two practical scenarios with and without a limit on the number of selected sites are considered. Finally, quadratic support function based iterative optimization approaches are developed to address the planning problems. Case studies in the modified IEEE 39-bus and 118-bus systems validate the effectiveness and efficiency of the proposed approaches under different scenarios by comparing with two other benchmarks.