Stability analysis and coordinated control strategy of Pelton turbine hydropower plants cascaded with regulating reservoir during power regulation

Pelton turbine hydropower plants cascaded with regulating reservoir (PHC-RR) offer a promising direction for high-head hydropower development in complex terrain. However, the stability mechanism of PHC-RR is not fully elucidated, and coordinated operation control strategies require further investigation. Herein, a stability analysis model for PHC-RR under power control mode (PCM) was established. The influence of inter-plant hydraulic interactions on stability was revealed. Subsequently, a power–water level coordinated control (PWLC) strategy was proposed by adding the regulating reservoir water-level deviation signal to the governor of the second-stage plant. Eigenvalue analysis and numerical simulations were used to verify the proposed strategy. Finally, stability domains of the control parameters were established, and concise analytical formulas were proposed for parameter tuning. The effects of the control parameters on the stability and dynamic characteristics of PHC-RR were analyzed. The results showed that the PHC-RR was unstable when both plants adopted PCM. The power regulation aggravated the discharge mismatch between plants, consequently inducing a sustained rise or fall in the regulating reservoir water level. The proposed PWLC strategy ensured fast and stable power regulation and suppressed the water level drift. The parameters kp1 and ki1 play a dominant role in governing the system stability and dynamic performance. kp2 and ki2 mainly influence the power regulation quality of the second-stage plant, which in turn affects the dynamic performance in the regulating reservoir water level. Increasing ki3 enhances the water level stability and accelerates its stabilization, thereby improving the power regulation quality of the second-stage plant.