Transient Stability Analysis Of Power System Based On Lyapunov Exponent

To assess the transient stability more effectively on the basis of obtaining the real-time dynamic response information of the power grid,an on-line transient stability identification method was proposed,in which Lyapunov exponent(LE)of the dynamical system was used to analyze the characteristics of rotor speed difference-rotor angle difference in the phase plane.Firstly,the maximum Lyapunov exponent(MLE)stability principle and calculation mechanism were introduced.Secondly,taking the single machine system as an example,the relationship between rotor speed difference-rotor angle difference characteristics and transient angle stability in different scenarios was analyzed strictly from the perspective of physical mechanism.Furthermore,based on the improvement of the MLE method by recursive least square algorithm(RLS)and the automatic optimization of parameters according to phase trajectory characteristics,the criteria of transient power angle stability were proposed,and the online identification method was formed.Finally,the method was extended to the multi-machine system by double machine equivalent.The proposed method is applicable to both first swing and multi-swing stability judgment problems,and it has strong fault tolerance to the generator grouping.More,in order to avoid homology units identification,the transient stability analysis of power system was transformed into MLE analysis problems of relative power angle trajectory of the key unit pair based on the definition of power system transient stability and the mechanism of MLE stability analysis.Firstly,the motion characteristics and physical mechanism of the unit pair under different transient scenarios were analyzed in detail,and the corresponding parameters of MLE calculation were set up by identifying the relative rotor speed mode quickly.Then,the reasonable stability criteria were put forward.Finally,the corresponding method of transient stability assessment was formed.The system equivalent,simplification,and homology units identification,are not required.It is effective for the problems of the first swing and multi-swing stability.And it is not necessary to determine the MLE symbol observation window in advance,which can be adapted to the complex and changeable power grid disturbance analysis.Further,in order to realize the decentralized transient stability analysis method based on the direct PMU measurement,transient angle stability analysis problem was first decomposed into MLE analysis problems of terminal voltage deviation curves of the severely disturbed generators based on phase space reconstruction and the relation between transient angle stability and change rate of voltage vs.voltage deviation(Vmagcr-?Vmag)characteristics.And the relevant parameter selection method of MLE calculation was proposed.At last,the rule of transient angle stability detection based on the MLE curves was provided.The system equivalent,simplify and homology units identification are not necessary in the proposed approach;Meanwhile,the shortcoming of setting up MLE sign observation window in advance has been overcome,which makes the approach more universal and practical.The simulation results verify the correctness and effectiveness of the proposed method.Finally,the three proposed transient stability analysis methods based on MLE were verified by the actual power grid simulation example,which shows that the proposed method is effective in real power grid.