Assessment of Grid Strength Considering Interactions between Inverter-based Resources and Shunt Capacitors

While the increasing penetration of renewable energy resources into the electric power grid improves energy efficiency and reduces greenhouse gas emissions, it may drive the grid towards weak power grid conditions, under which grid stability issues may affect the operation of inverter-based renewable generators. The short-circuit ratio (SCR) with some modifications has been used to analyze power grid strength. However, the existing SCR-based methods for grid strength assessment neglect the impact of the interactions between shunt capacitors interconnected through the power network, which may cause over-optimistic results of grid strength assessment. To account for the impact, a novel method for grid strength assessment is proposed in this paper by theoretical analysis of how the interconnected capacitors affect static voltage stability. The efficacy of the proposed method is demonstrated through numerical simulation case studies on the IEEE 39-bus system.