Study On Nonlinear Dynamics Of Power Systems With Large Scale Wind Farm

Nonlinear theory is the important method and hot topic to analyze thedynamic stability of power system. With the growing scale of the powersystem, large scale wind turbines and other new energy power connectedto the power systems, the power systems is more and more uncertain andnonlinear. Under certain conditions, the bifurcation or chaotic phenomenawill occur, which will threaten the security of the power system seriously.The purpose of this thesis: Firstly, establish the differential-algebraicequations of wind power system and explore the relationship betweennonlinear dynamic behavior of wind power system and voltage oscillationof wind power system. Secondly, Research the bifurcation and even chaosmechanism induced by the wind power system. Finally, for the nonlinearcharacteristics of wind power system, an effective method of variablestructure control which is used to inhibiting the bifurcation and chaos ofwind power systems is proposed.The main contents of this study include the following sections:(1)The dynamic model of the wind power generation system isestablished. Grid dynamic mathematical model of the single double-fedwind turbine and the single permanent magnet direct drive wind turbine iscreated, which include generators, converters and pitch angle dynamicmodel. And the equivalent models of large-scale grid-connected wind farmsare established, the method of calculating the equivalent of each parameteris described in detail.(2)The differential-algebraic equations of permanent magnet directdrive wind farm and double-fed wind farm power system is established,the equilibrium solution manifold of wind power system is tracked, studied the conditions and mechanism of the bifurcation point and chaos whichappear on equilibrium solutions manifolds. In order to improvecomputational efficiency, an improved algorithm which is used fortracking equilibrium solutions manifolds is proposed. Pointing out thatbifurcation and unstable phenomenon of the power system will occur withparameter changing. The study also shows that the increasing of windturbines and the changing of converter parameters lead to the subsynchronous resonance and low-frequency oscillation phenomena in system.Based on the study, the solution to relieve the both phenomena is proposedand confirmed in the actual wind farm. The study of the dynamiccharacteristics provides a theoretical basis for the actual wind farm.(3)The math model is combined with Ningxia Jiaze station wind farm.The field test is carried out and the experimental data show that therereally are bifurcation and chaos in large-scale wind power system.According to reconstructing the phase-space of experimental data, findingout the attractor and calculating maximum Lyapunov exponent of variousstages, the dynamic attribute of various stages voltage in the experiment.(4) Based on the fuzzy adaptive variable structure control method, theeffective control of wind power system is implemented. The control strategyis the integration of fuzzy complex switching function and self-adaptationcontrol in the system to control chaos phenomenon. The study shows thatthe response speed and the control precision of this control strategy arebetter than conventional linear feedback control.