Research On Nonlinear Mechanism Of Power System Low Frequency Oscillation And Its Control Strategies

Safe and stable operation of power grid is a guarantee of the steady growth of national economy. However, with the expansion of power grid interconnection and the gradual growth of complicated running environment, swing oscillation between interconnected power grids brings severer problems to power system safety and stability. As a typical strong coupling, highly nonlinear and multi-variable dynamic system, power system has a series of complex nonlinear dynamics behaviors and nonlinear physical characteristics of the system itself are important causes of LFO. In this thesis, the research focuses on the application of chaos theory to power system. Through theoretical analysis and simulation, nonlinear mechanism of power system LFO is explored, LFO characteristics of chaotic system is analyzed and chaos control method is applied to realize power system LFO control.First, from the angle of bifurcation and chaos theory, related research results of LFO of nonlinear mechanism are summarized. Bifurcation and maximum Lyapunov index diagram that reveals the effect of disturbance intensity and power system damping parameters on chaotic characteristics of the system are obtained. Besides, time domain diagrams and phase diagrams of generator angle under typical bifurcation parameter values are analyzed to show corresponding phenomena like single mode, multiple modes and instability in LFO in the process of nonlinear system bifurcation and chaos. Two common LFO analysis methods, sliding window FFT method and the Prony method are adopted to calculate such LFO characteristic values as oscillation frequency, amplitude and attenuation coefficient under chaotic situation. With a fully grasp of system characteristics, different control methods are adopted respectively in 2 dimension and 4 dimension chaotic system to control and restrain LFO caused by chaos. Simulation analysis shows that the controller designed in this thesis can effectively eliminate chaos and suppress LFO in power system and will lead the system to a stable state when there is disturbance.