Research On Voltage Stability Analysis And Control Strategy Of Power System Based On Bifurcation Theory

In twenty-first Century,with the development of industry and information technology and the continuous improvement of living standards,industrial production equipment,home appliances etc.put forward higher requirements to the quality of power supply.Providing more secure,stable and reliable electric power has become the direction of related technology research work of modern power system.Voltage,frequency and harmonic are three measurements of the quality of power system.Since several voltage instability accidents happening in the world caused serious influence on the society production and people’s common life,in recent years,the voltage stability of power system has attracted more and more attention from all sectors of society and the i nternational society of electrical engineering.With the development of the power industry,the modern power system has developed to larger power grid,larger unit,and extra high voltage and long distance transmission.Because of varieties of distributed power supplies,new energy grids and reactive power compensation devices,the operation condition and dynamic factors of power system have become more and more complicated,which prone to voltage instability of power grid.Under this circumstance,this paper have considered various of uncertain factors and dynamic effects in actual conditions,such as dynamic load,dynamic characteristics of generators and reactive power compensation devices,and electromagnetic power disturbance.Using the bifurcation analysis method of dynamic voltage stability and the time domain simulation and chaos theory as a supplement,the process and mechanism of voltage instability in a variety of load conditions,load margin and power transmission limit on two different kinds of power system models are analyzed.Based on the analysis above,two nonlinear voltage stabilizing controllers are designed using the finite time stability theory and the asymptotic stability theory of diagonal matrix,and the effectiveness of controllers are verified by numerical simulations.Firstly,established the power system model with static var compensator(SVC)and PQ dynamic load,and the system was assumed to be subject to electromagnetic power disturbance.Chose the reactive power compensation system gain k SVC and reactive load Qd as bifurcation parameters(control parameters)of the system,we obtained mechanisms of voltage instability and collapse by u sing bifurcation and chaos theory to analyze the one-dimensional equilibrium solution manifold voltage curves and time domain simulation diagrams of the system.And we obtained the limit of voltage stability,reactive power load margin and adjustment margin of SVC gain under multi-parameter variations by using two dimensional bifurcation curves.To improve stability of the system,we have also designed a nonlinear voltage stability controller based on the finite time stability control principle,and the controller was proved to have good control effect by numerical simulation s.Secondly,we improved the system model with Walve dynamic load to be the mathematical model with three uncertain parameters.The voltage stability and operation state variations under multiple load conditions were analyzed through system voltage curves,state trajectories,the largest Lyapunov index and bifurcation diagrams.We also obtained the voltage stability boundary,power transmission limit,load dynamic regions by two-parameter and three-parameter voltage analysis.Finally,A new nonlinear voltage stabilizing controller is designed,which is based on the principle of asymptotic stability of diagonal matrix.By Matlab numerical simulations,the controller can effectively improve the voltage stability of the power system with Walve dynamic load,and has strong robustness as well.