Control of the Ultra-Low Frequency Oscillation in Southwest Power Grid of China Based on Damping Characteristic Analysis

At the end of 2018, the Southwest Power Grid will asynchronously interconnect with the State Grid, and the tests show that it exists a high proportion of ultra-low frequency oscillation (ULFO), which threatening the operation of system. Based on the governor system model, the negative damping mechanism of ULFO is analyzed, and the suppression measure of adjusting the PI parameters of governor system is given. The details are as follows: in this paper, the phenomenon of ULFO in the Southwest Power Grid is introduced. And then based on detailed model, the mechanical damping coefficient of the governor system of each generator under the ultra-low frequency is calculated. The results show that the negative damping provided by hydro-turbine governor system is one of the main reasons causing the oscillation. Furthermore, the impact of PI parameters of governor system on the damping characteristics of hydropower generators is analyzed. Moreover, the idea to suppress ULFO based on adjusting the PI parameters is given, together with the considering for the influence of parameters on the transient and steady-state characteristics. Finally, simulation results show that the proposed PI parameters adjusting method to governor system could suppress the ULFO.