Research On Nonlinear Dynamic Characteristics Of Swing Oscillation Of Synchronous Generator In Power System

Recently, electric power systems have become more huge and complicated. Stability problems have become more complex as interconnections become more extensive. Modern power system is forced to operate close to its stability limit due to the growth of power demand and other constraints for building new power plants and transmission lines, such as environment, technique and economic. Therefore, the stability of electric power systems has been received much attention in scientific studies. The power angle stability in power system is closely related to the mechanical movement of the synchronous generator rotor,which is always the focus of the stability research of power systems. Many instability accidents are caused by loss of stability of the power angle of the synchronous generator. The swing motion of the generator rotor with many oscillation forms, such as principal resonance and combination resonance, which may easily lead the synchronous generator lose synchronization or the whole power system lose its stability. Power system is essentially a typical complex nonlinear dynamic system, which displays very rich dynamic behaviors. Thus, it has very important significance to conduct some researches about the swing oscillation of synchronous generator rotor by using nonlinear dynamical theory.In this dissertation, some nonlinear dynamic behaviors exist in the motion equations of synchronous generator rotors(also called swing equation) in small or large-scale power systems are investigated in detail by analytical and numerical approaches. The purpose of this dissertation is to explore some nonlinear dynamic behaviors and their mechanisms of the swing oscillation, which may lead the synchronous generator loses synchronization.The bifurcation and chaotic characteristics of the swing equation are studied in a single-machine infinite-bus(SMIB) power system under periodic load disturbance. Considering the impact of the system state variables on the damping power of the synchronous generator, the modified swing equation is established. The approximate periodic solution of oscillation with small amplitude and the bifurcation equation are obtained by using the method of multiple scales. Based on the bifurcation equation, the singularity analysis is carried out by applying the singularity theory. With the help of Melnikov mehod, the analytical threshold for the onset of ch aotic motion is given. The influences of the periodic load and the damping coefficient on the system’s dynamic behaviors are also discussed through numerical simulation.And on this basis, the swing equation of a SMIB power system with two frequency excitations is established. The two frequency excitations come from the periodic load disturbance and the input periodic mechanical power. Because the mechanical power input is disturbed periodically by considering the moderating effect of the prime motor. The bifurcation characteristics of the combination resonance under certain combination frequency condition is analyzed by using the method of multiple scales. The results show that both of the amplitude of the periodic load and the amplitude of the periodic mechanical input power have important effects on the system response. When both of them are small, the system response has periodic solution with small amplitude. There exist the multiple-valued, jumping and hysteresis phenomena, which may make the system lose its stability easily. The investigation also shows that the chaotic motion may occur easily in the considered system.For the two-machine quasi-infinite-bus power system, the voltage maganitude and phase of the infinite bus are considered to maintain t wo fluctuations in the amplitude and frequency. The swing equation with two degrees of freedom is established. The case of 1:3 internal resonance between the two modes, in the presence of parametric principal resonance is considered and examined. The method of multiple scales is applied to obtain the bifurcation equations of this system. Then by employing the singularity theory, the transition sets determining different bifurcation patterns of the system are obtained and analyzed, which reveal the effects of the infinite-bus voltage amplitude and phase fluctuations on bifurcation patterns of this system. Owing to occurrence of 1:3 internal resonances, the first-order mode amplitude is considerably larger than that of the second-order mode. The solution of the coupled modes of the two-machine quasi-infinite-bus power system have more critical bifurcation points and have quite rich bifurcation patterns.Taking into account the three-machine infinite-bus power system, its dynamic performance is analyzed as the system parameters changed. With the help of global bifurcation diagram, largest Lyapunov exponent, time history, phase portrait, Poincaré mapping and frequency spectrum, the effects of the perturbation amplitude and perturbation frequency of the infinite-bus voltage, the effect of the damping coefficient on the dynamic behaviors of the considered system are investigated in detail.It is a new perspective to using the singularity theory to study the angle stability of the power system, which provides a new method for study the effects of the system parameters on the power system dynamic characteristics, system stability and control analysis. The results obtained in this paper will contribute to a better understanding of the mechanism of the forced power oscillation in power system.