Operation control and performance evaluation of variable-speed pumped hydro compressed-air hybrid energy storage system

This study addresses the challenge of significant head variability in hydraulic machinery within variable-speed pumped hydro compressed-air energy storage systems. Departing from conventional fixed-efficiency or constant-flow assumptions, an integrated speed–guide-vane control strategy is introduced, based on comprehensive manufacturer-supplied characteristic curves. First, a numerical simulation model was established to account for the operational characteristics of each component and subsequently validated. Next, efficiency optimization measures were implemented, resulting in a coordinated speed-opening control strategy. Additionally, power control laws and numerical methods were developed for three representative load variation scenarios, which were followed by detailed operational performance evaluations. Finally, energy and exergy analyses provided insights regarding the distributions of work and exergy flows across system components, while highlighting optimization priorities. Findings revealed that the proposed control strategy effectively expanded the operating head range to 9.74–21.43 m, with speed regulation spanning 1887–2737 r/min. Across the three cases, the magnitude of power changes gradually decreased, and both energy and exergy performance metrics improved. In the optimal scenario (Case 3), the system achieved an η_RTE of 0.631 and an η_X of 0.648. Exergy analysis highlighted that the variable-speed pumped storage unit accounted for 38.8% and 22.8% of the system's primary sources of exergy destruction during charging and discharging, respectively, representing a critical area for further performance optimization.