A Novel Hybrid Event-Based System Separation and Response-Driven Under-Frequency Load Shedding Scheme in a Standalone Power System With Renewables

The increasing integration of renewable energy sources into power systems, driven by their clean and sustainable attributes, has attracted significant attention. However, during severe contingency events, renewable resources such as photovoltaics (PV) may trip prematurely due to their own protection strategies, potentially occurring before load shedding and leading to cascading outages. This paper presents a novel hybrid special protection scheme (SPS) for autonomous (standalone) power systems with renewables. The proposed approach combines an event-based system separation strategy with a response-driven under-frequency load shedding (UFLS) strategy to mitigate premature renewables tripping, thereby preventing catastrophic cascading load shedding. Hybrid particle swarm optimization is employed to determine the optimal splitting points in the power system. Additionally, the total shed loads at all steps of 81L relays in the separated areas are minimized, while the average frequency nadir across all separated areas is maximized. The uncertainty in PV power generation is modeled using probabilistic methods to account for various scenarios. The effectiveness of the proposed method is demonstrated using a 31-bus standalone power grid with a total demand of 66.62 MW and PV power generation of 7.61 MW. The results show that the proposed method sheds only 11.30 MW of load and trips 2.18 MW of PV power generation, compared to 25.28 MW of load shedding and 6.47 MW of PV tripping observed in existing methods under high irradiance conditions.