Stability and dynamic characteristics of the nonlinear coupling system of hydropower station and power grid.

• Mathematical model for nonlinear HTGS–PG coupling system is established. • Stability is studied by using stable domain and verified by numerical simulation. • Generation mechanism of two time scales oscillation of system is revealed. • Effect of HTGS and PG on stability and dynamic characteristics of system is analyzed. This paper aims to study the stability and dynamic characteristics of the nonlinear hydro-turbine governing system (HTGS)–power grid (PG) coupling system. Firstly, for the coupling system, the nonlinear mathematical model considering the nonlinear characteristic of head loss in the penstock is established. Then, based on the nonlinear mathematical model and Hopf bifurcation theory, the stability is studied by using stable domain and verified by numerical simulation. Finally, by investigating the dynamic characteristics, the generation mechanism of two time scales oscillation of nonlinear HTGS–PG coupling system is revealed. The effect of HTGS and PG on the stability and dynamic characteristics of system is analyzed. Sensitivity analysis of nonlinear HTGS–PG coupling system to noise and variability of system parameters is conducted. The results show that, for nonlinear HTGS–PG coupling system, the emerged bifurcation is supercritical and the area at the bottom side of bifurcation line is stable domain. The nonlinear HTGS–PG coupling system possesses two time scales oscillation, i.e. subwave-1 with a low frequency and subwave-2 with a high frequency. Subwave-1 and subwave-2 are generated by PG and HTGS, respectively. The HTGS and PG have coupling effect on the stability and dynamic characteristics of the two time scales. The stability and dynamic characteristics of nonlinear HTGS–PG coupling system can be significantly improved by the reasonable determination of system parameters. The nonlinear HTGS–PG coupling system is the most sensitive to the variability of HTGS parameters, especially to e y and e qy. [ABSTRACT FROM AUTHOR]