Dynamic simulation of a hydropower plant cluster with a pumped-storage unit: A case study in Greece

• A dynamic Modelica model for both conventional and pumped-storage HPPs is developed. • The model captures frequency response (±3.4 mHz frequency deviations), control actions, and operational constraints (voltage within ±0.06% of nominal). • Novel clustered operation of Greek HPPs (Ilarionas, Pournari, Thissavros) under real demand profiles. • The model supports analysis of HPPs, both long-term and short-term. • Droop control enables stable frequency regulation in multi-unit systems (20% load disturbance tested). Pumped-storage hydropower (PSH) offers significant advantages to modern power systems by providing large-scale, long-duration energy storage with high efficiency and long service life. This paper presents a dynamic simulation study of a Greek hydropower cluster comprising three plants, interconnected with the transmission grid and including both conventional and pumped-storage hydropower units. The model is implemented in Modelica, parameterised with plant-specific data, and driven by actual transmission-level profiles for grid representation. Two operation modes are analysed: (i) long-term scheduling with variable load profiles, and (ii) short-term response to a 20% step load disturbance. The long-term simulations reproduce actual system behaviour, with frequency deviations constrained within ±3.4 mHz and voltage fluctuations within ±0.06%. In the short-term case, coordinated hydropower operation improves frequency nadir by 0.38% (49.603 Hz compared to 49.415 Hz without hydropower), reduces the rate of change of frequency by 88%, and shortens recovery time by 40%. These results demonstrate the complementary roles of conventional and pumped-storage units in primary frequency control and underline the contribution of clustered hydropower to ancillary services and overall grid reliability.