Non-Anticipative Flexibility Assessment of Hybrid Pumped-Storage Hydropower Plants via Storage-Envelope Certification

Hybrid pumped-storage hydropower plants can provide substantial flexibility for renewable energy integration, but their available power range is strongly coupled with reservoir dynamics and future grid requests. This paper proposes a non-anticipative flexibility assessment method for constructing a multi-period active power request region that can be reliably tracked under causal operation. A sufficient storage-envelope certificate is developed for a continuous aggregate plant model, ensuring that every request trajectory within the resulting hyperrectangular region can be followed using only information available up to the current period, while satisfying hydraulic constraints and terminal storage requirements. Under the stated hydraulic and spill assumptions, monotonicity of the one-period storage transition set reduces the semi-infinite forward-invariance conditions to endpoint dispatch checks. The resulting single-stage nonlinear formulation is implemented as a mixed-integer linear program using piecewise-linear approximations. The certified active power intervals are further used to construct compatible active–reactive power capability regions. A case study based on the Baishan–Hongshi hybrid pumped-storage hydropower plant in China shows the effectiveness of the proposed method. The resulting capability region can help operators screen requested power profiles and set defensible day-ahead or intraday flexibility limits, while the storage envelope provides a state-dependent rule for causal scheduling-level redispatch that preserves deliverability later in the horizon.