Flexible Day-Ahead Scheduling of a Cascade Hydro-Wind-Solar-Thermal-Storage System Including Hybrid Pumped Storage

To advance the modernization of power systems, the role of hydropower has transitioned from mere energy generation to serving as both a primary energy provider and a critical flexibility resource. However, conventional day-ahead scheduling methodologies for cascaded hydropower often prove inadequate in mitigating the short-term power imbalances induced by renewable energy variability, primarily due to an oversimplification of operational constraints. To fully harness the regulatory potential of hydropower, this paper proposes an optimal day-ahead scheduling strategy for a cascade hydro-wind-solar-thermal-storage system incorporating hybrid pumped storage (HPS). First, leveraging the operational characteristics of HPS, this study evaluates its capacity for renewable energy accommodation and identifies key challenges in power balancing from the perspectives of water resource management and energy dispatch. Second, a collaborative optimization framework is established. By introducing the concept of an “allowable reservoir water level fluctuation range” within the day-ahead dispatch cycle, the framework constrains the deviation between the actual end-of-period water level and its predefined target, thereby ensuring strict adherence to medium-to-long-term operational boundaries. Finally, case studies conducted on a modified IEEE 33-node system demonstrate that the integration of HPS significantly enhances system regulation capabilities. The results confirm that the proposed strategy contributes to secure, economical, and low-carbon grid operation while maintaining reservoir sustainability.