A novel two-stage framework for real-time adjustment of cascade hydropower stations in response to frequent grid load fluctuations

With rapid renewable energy growth, power grids face frequent load fluctuations from wind and photovoltaic uncertainties. Cascade hydropower stations serve as "flexibility providers" to balance these fluctuations through load adjustment. However, existing real-time strategies focus on station-level without unit-level refinement, causing frequent startup/shutdown operations and inability to avoid vibration zones. Additionally, adjustment focuses only on current periods, compromising daily water level and power generation targets. This paper proposes a novel two-stage "inter-station to intra-station" framework for real-time fine-grained load adjustment. At inter-station level, station participation sequences are determined based on end-of-period water level targets and daily contracted power, with strategies formulated according to individual station flexibility. At intra-station level, a comprehensive evaluation model determines unit startup/shutdown sequences, followed by unit combination selection and load optimization distribution considering vibration zone crossings to achieve fine-grained adjustment from cascade to unit level. The framework is validated using “Hongjiadu-Dongfeng-Suofengying” cascade stations in Wujiang River basin. Results demonstrate effective reduction of end-of-period water level and daily contracted power deviations, 68.8% decrease in vibration zone crossings, and 16.7% reduction in unit operations. The framework provides systematic foundation for cascade hydropower load adjustment in high renewable penetration grids.