A comprehensive evaluation framework from design to operation: Enhancing the regulation performance of variable-speed pumped storage plant in extreme pumping conditions

Compared to fixed-speed pumped-storage units (FSUs), variable-speed pumped-storage units (VSUs) provide superior power adjustability in pumping mode. However, poor hydraulic stability poses a challenge to the widespread application of VSUs. Unlike previous research that only examines single aspects of VSU performance, this paper presents a comprehensive three-dimensional evaluation framework that quantifies and improves VSU resistance to hydraulic disturbances in pumping mode. This framework integrates previously disconnected subsystems including control strategies, unit combinations, and structural arrangements, providing a systematic approach to comprehensively evaluate VSU hydraulic performance. Through this research, several original insights are obtained: In control strategies, the impact of initial operating speed and control parameters on stability during pump power-off is studied. Contrary to conventional understanding, results indicate that increasing Kp helps maintain the stability of input power and speed, whereas increasing Ki is detrimental to input power stability but beneficial for speed stability. In evaluating unit combinations, differences in regulation stability between VSU + FSU and FSU + FSU schemes are assessed, revealing that while VSUs maintain shorter durations of power exceedance, they experience more pronounced speed fluctuations than FSUs. Within the safety range, a larger guide vane closing rate helps mitigate these fluctuations. Regarding structural arrangements, the study examines the effects of shared diversion pipes, shared draft pipes, and arrangements with both diversion and draft pipes shared on hydraulic disturbances. In the case study, the shared draft pipe arrangement effectively enhances the unit’s resistance to hydraulic disturbances, improving speed stability by at least 63% and power stability by at least 48.7% compared to other schemes. This innovative framework illustrates the relationship between intrinsic regulation characteristics and external parameters, providing valuable references for the design and operation.