Multi-frequency oscillation characteristics and stability of the pumped storage power station based on a theoretical analytical method

The pumped storage power station is a complex hydraulic-mechanical-electric coupling system. The coupling effect between subsystems causes the pumped storage power stations to exhibit multi-frequency oscillation characteristics, making stable operation challenging. However, the widely-used eigenvalue analysis, hydraulic vibration analysis, and the Fourier transform methods cannot comprehensively distinguish and quantify the multi-frequency oscillation characteristics of pumped storage power stations. This study aimed to propose a theoretical analysis method to comprehensively investigate the multi-frequency oscillation characteristics and their main influencing factors. First, the mathematical model of a pumped storage power station with upstream and downstream surge tanks was established. Then, a multi-frequency oscillation method for deriving the theoretical formula for the dynamic response was introduced, and verified via numerical simulation. The dominant oscillations in the dynamic response were accurately identified. The results showed that the system was supposed by six frequency oscillations (S1 - S6), and the dynamic response of the rotational speed consisted of a major wave and a tail wave. The major wave was determined by the S1 and S6 oscillations, and the tail wave was determined by the S3 oscillation. Finally, the main factors influencing the multi-frequency oscillations were investigated. The governor parameters and penstock water inertia significantly influenced the S1 and S6 oscillations and thus the major wave. The tailrace tunnel water inertia significantly influenced the S3 oscillation and thus the tail wave. Overall, the proposed method not only enhances our understanding of hydraulic-mechanicalelectric coupling multi-frequency oscillations, but also has important engineering value for ensuring the stable operation of pumped storage power stations.