Analysis and Control to the Ultra-Low Frequency Oscillation in Southwest Power Grid of China: A Case Study

The ultra-low frequency oscillations(ULFO) are found in the future Southwest Power Grid under some faults, which will asynchronously interconnect with the State Grid via the HVDC and VSC-HVDC before the end of 2018. In this paper, the phenomenon of ULFO in the asynchronous interconnected Southwest Power Grid is introduced. And then, with the oscillation energy flow and the amplitude-phase analysis for the ULFO, the energy characteristics of each power plant participating in ULFO are revealed, i.e., the ULFO are mainly between the hydropower plants and the thermal power plants. Furthermore, with the analysis of damping characteristics of main hydropower plants, the cause of the ULFO, i.e., lacking of damping in the hydropower plant is revealed. Upon the above results, an example of suppressing the ULFO with the approach of control parameters tuning for the governor of the dominant generators is presented.