Research on Ultra-Low Frequency Oscillation Caused by Hydro Power in Hydro-Dominant Power System

There is a rare frequency problem in the Southeast power grid which is with a high ratio of hydropower penetration. The prominent negative damping effect of hydro unit causing the emergence of ultra-low frequency oscillation (ULFO), the frequency of which is less than 0.1Hz has been studied. The detailed SMIB system of hydro unit based on linear hydraulic turbine model and the type-8 governing system in PSASP has been established. The main factors, which mostly influence the system damping level including water hammer effect and the operation level especially the output power of hydro unit have been researched. According to the simulation results, the dynamic characteristics of frequency responses and output active power fluctuation are analyzed and effects of the main factors on ULFOs are concluded. Finally, the proper suggestions on adjusting the hydropower scale and operation modes for hydro-dominant power system stability are proposed.