Medium to long-term optimization model and scheduling strategy for cascade hydropower plants under high penetration of variable renewable energy

The integration of high penetration of variable renewable energy (VRE) into cascade hydropower plants exacerbates the need for operational reliability, necessitating decision support technologies to manage the increased complexity. This study proposes a medium to long-term optimization model for a hydro-wind-photovoltaic system to accommodate high VRE penetration. The model employs a logical constraint approach to balance water spillage and power curtailment, and a Variational Time Scale (VTS) framework is developed to improve computational efficiency. Model validation and scheduling strategy analysis confirm that the model boosted computational efficiency, reduced water spillage and prevented unnecessary spillage when the reservoir was not full. The optimization model successfully facilitated the transition of hydropower from the flood season to the pre-flood period, and significantly increased the total power generation by reducing the power curtailment during flood season. The differences in the regulating capacities of hydropower plants and variations in hydrological conditions have a significant impact on scheduling strategies. In wet years, the reservoir water level tends to drawdown more deeply, often entering the drawdown phase as early as February. These results confirm the active compensation potential of cascade hydropower plants under high penetration of VRE.