Study On Conservatism Evaluation And Efficiency Improving Method Of Lyapunov Stability Criteria For Time-delay Power System

With the rapid development of China's power utilities,effective coordination control via wide-area measurement control(WAMS)plays an important role.However,the extensive time delays in WAMS bring stability hidden danger.Among all stability analysis methods for the time-delayed system,Lyapunov stability theory and linear matrix inequality(LMI)method are commonly used today,which can evaluate the system stability directly,but with unavoidable conservativeness.In this thesis,influence of the items in Lyapunov function on the conservatism of stability criteria is analyzed to explain the difference in conservative properties and to provide guidance for seeking better criteria.The main research work is illustrated as follows:(1)On the basis of detailed mathematical models of power system,the time-invariant models are constructed via linearization technique for the following research.Four LMI criteria,as well as Lyapunov functions are derived to analyze the power system stability with time delay.(2)A diversity-based quantitative evaluation method of conservatism of time-delayed stability criteria for power systems is proposed.This method contains three procedures: calculating state trajectories of the time-delayed power system,normalizing Lyapunov functions and calculating three kinds of indices.The method can evaluate the conservatism diversity of the stability criterion without computing the time-delayed stability margin.The correctness and the effectiveness of the proposed method is validated by three cases.(3)A method for improving efficiency of time-delayed stability criterion based on weight value analysis of Lyapunov function items is proposed.First,a numerical calculating method is used to study the time-varying properties of each item in the Lyapunov function to obtain the corresponding weight.Then redundant items in the function are identified and deleted to improve the efficiency of the stability criterion without increasing its conservatism.Finally,the method is used to improve two time-delayed stability criteria,and the verification is also provided.