Abstract
The main merit of grid-connected adjustable-speed pumped storage unit (ASPSU) is the capability to control the pumping power flexibly, which contributes to active power balance in power system operation. Physics-based dynamic modeling of ASPSU in pumping mode under power regulation is the foundation of the quantitative analysis on its transient performance, which has been studied inadequately. This study aims to derive a dynamic model of ASPSU in pumping mode which embodies reversible pump-turbine characteristics, and to conduct eigen analysis on ASPSU in pumping mode which facilitates a better understanding of its intrinsic dynamics. Firstly, the dynamic model of reversible pump-turbine is revealed to depict its regulation properties that the pumping power is adjusted by rotational speed rather than guide vane opening. Then, the state-space representation of ASPSU in pumping mode is established to be utilized with small disturbances (including indicial and ramp tests) and validated by comparing simulated results with actual records of a commissioned ASPSU in Japan. It is also effective for compensating the wind power fluctuations based on a timescale of seconds in simulation. Finally, the eigenvalues, damping ratios, and participation factors of the state variables are investigated based on the small-signal-stability model of ASPSU in pumping mode under power regulation. The results of eigen analysis indicate that the small-signal behavior of the system is characterized by electromechanical mode and electromagnetic mode, and the latter is dominant. Moreover, the damping ratio of electromagnetic mode which is sensitive to system stability needs to be increased.
Highlights
Rocketing penetration of renewable energy sources with the intermittent nature into power system brings new challenges to active power balance
adjustable-speed pumped storage unit (ASPSU) is usually composed of an alternating-current (AC) excitation induction machine and a reversible pump-turbine, as illustrated in Fig. 1 [6]
Following the fact that the pumping power of reversible pump-turbine is tuned by rotational speed rather than guide vane opening, some reports presented that the pumping power is proportional to the cube of the runner speed depending on the affinity law [5], [19]
Summary
Rocketing penetration of renewable energy sources with the intermittent nature into power system brings new challenges to active power balance. The reversible pump-turbine has adjustable guide vanes controlled by the speed governing system and fixed runner blades In this way, two parts are mainly concentrated on in the dynamic modeling of ASPSU under power regulation. Following the fact that the pumping power of reversible pump-turbine is tuned by rotational speed rather than guide vane opening, some reports presented that the pumping power is proportional to the cube of the runner speed depending on the affinity law [5], [19]. Physics-based dynamic modeling of ASPSU in pumping mode under power regulation is still required for the simulation, the controller design, and the quantitative analysis on its transient performance. (2) The physics-based dynamic model of ASPSU in pumping mode under power regulation is proposed and validated by comparing simulated results with practical records in indicial and ramp tests, respectively.
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