Abstract: To address the problem of low-frequency and ultra-low-frequency oscillations (ULFO) in hydropower unit regulation systems (HURS) with a shared draft tube system (one tunnel, two units), a new control parameter optimization strategy for HURS based on the Improved Salp Swarm algorithm (ISSA) is presented. ISSA enhances search performance by incorporating two improvement frameworks: a cultural gene algorithm and a chaotic sequence, enabling it to explore the optimal solution within the search space. A simulation case study of HURS includes three parts－frequency regulation mode, power regulation mode, and gate opening regulation mode－with a comparative analysis of the simulated responses before and after optimization to validate the feasibility and effectiveness of this optimization method in controlling the HURS parameters of shared draft tube systems. The simulation results show the optimized system reduces the number of oscillations by at least 50% in each regulation mode and significantly improves the operational stability of the units.

Key words: hydropower units, low-frequency oscillations, PID parameter optimization, Salp Swarm algorithm