Abstract
The dynamic characteristics of hydropower unit governing systems considerably influence the stability of hydropower units and the connected power system. The dynamic performances of hydropower units with power regulation mode (PRM) and opening regulation mode (ORM) are different. This paper establishes a detailed linear model of a hydropower unit based on the Phillips–Heffron model. The damping characteristic and stability of two regulation modes with different water inertia time constants TW were analyzed. ORM tended to provide negative damping, while PRM often provided positive damping in the major parts of the frequency range within the normal frequency oscillations when TW was large. Eigenvalue analysis illustrated that PRM has better stability than ORM. To validate the analysis, a simulation under two typical faults WAS conducted based on a nonlinear model of a hydropower unit. The simulation results illustrated that the responses of units with PRM are more stable in terms of important operating parameters, such as output power, rotor speed, and power angles. For hydropower units facing challenges in stable operation, PRM is recommended to obtain good dynamic stability.
Highlights
With the strong demand for clean and green energy, hydropower energy has experienced rapid development in recent years
While this study was concerned with the isolated system and neglected the electromagnetic transient process, Chen et al analyzed the stability of hydropower units with different regulation modes and found that the stability of pure power regulation modes are clearly superior to frequency regulation modes under the same conditions [26]
In reference [23], the frequency stability of the hydropower unit in an isolated power system was analyzed, neglecting the electromagnetic transient process and variable operating parameters, whereas we studied a large-scale power system and analyzed the power angle stability
Summary
With the strong demand for clean and green energy, hydropower energy has experienced rapid development in recent years. Strong nonlinear characteristics pose a challenge for the smooth and accurate control of hydroturbines With such inherent defects, various unstable phenomena caused by hydropower units have been observed in hydropower-domain power systems, such as low frequency oscillations and power fluctuations. Research on the dynamic characteristics of different regulation modes is required to provide some guidelines for the hydropower units in hydropower-dominant power systems. While this study was concerned with the isolated system and neglected the electromagnetic transient process, Chen et al analyzed the stability of hydropower units with different regulation modes and found that the stability of pure power regulation modes are clearly superior to frequency regulation modes under the same conditions [26]. Whereas the pure power mode only aims to control power and regards the frequency deviation as unavailable in real power grids, in a previous study, characteristic analysis and comparison of ORM and PRM was far from sufficient. The numerical simulation, based on real nonlinear models, proved the results
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