Study On Data-driven Small Signal Stability Analysis And Damping Enhancement Strategy For Interconnected Power Systems

Small signal stability is one of the important issues that threaten the safety and stability of power systems.With the expansion of interconnected power grids and injection of large-scale renewable energy,modern system scale becomes larger,the operation of power systems changes more flexible,and the system model gets more complicated,making small signal stability issue remain an important engineering problem which needs to be solved urgently for power system operating.The development of wide-area measurement system provides a favorable platform for realizing online stability analysis and control of small signal stability.Furthermore,wide-area ambient data is the dynamic response while the system input is from continuous small random fluctuations in loads,the intermittent outputs of renewable energy and other related small variations which are assumed to be ambient excitations.Ambient data are continually available and has abundant data,and more importantly,it can reflect the dynamic characteristics of power systems under its normal operating conditions.To this end,based on the ambient data of power systems,this paper focuses on the small signal stability online evaluation and damping modulation of interconnected power grids.By fully mining and effectively utilizing the wide-area ambient data,we can timely track the electromechanical small stability characteristic parameters and grasp the small signal stability level under the current operating condition.Therefore,based on the online tracking results of mode estimations,the potential satefy and stability issues can be discovered,then effective control measures should be taken to improve the system damping level.The main work in the dissertation is as follows:(1)Based on the stochastic differential equation and power system ambient excitation characteristics,the analytical expression of ambient data of power systems under the ambient excitation is derived.Considering the similarity of power system network and mechanical vibration system,the analytical expression of power density spectrum of ambient data is derived based on the random vibration theory,which proves the existence of electromechanical information in ambient data from frequency-domain aspects,and reveals the mechanism of extracting the electromechanical characteristic parameters utilizing ambient data.It provides a solid data foundation for stability evaluation and damping modulation of power systems based on the ambient data.(2)Ambient data-driven small signal stability on-line evaluation method for interconnected power systems is studied.By utilizing the wide-area ambient data of power systems as the data source,subspace dynamic mode decomposition(Sub-DMD)method for analyzing fluid characteristics is introduced into power systems,and the system state space matrix can be extracted online by Sub-DMD.Meanwhile,to further improve the real-time performance of small signal stability evaluation,Givens rotation is introduced,and an online recursive tracking method for state matrix of power systems based on recursive subspace dynamic mode decomposition(Rsub-DMD)is proposed.The proposed Rsub-DMD method realize online extraction and tracking of electromechanical small signal stability characteristic parameters.In addition to reliably extract electromechanical parameters,it greatly improves the real-time performance of small signal stability online evaluation of power systems.(3)Aiming at the difficulty in online determination of active power adjustment in generation rescheduling,an online estimation method for rescheduling amount based on the interarea transmission capacity(ITC)evaluation considering small signal stability constraints is proposed.Firstly,based on ambient data,a simplified equivalent two-machine system(ETm S)model of interconnected power systems is constructed.Then,on the basis of construction of the ETm S,we develop an optimization model for online evaluating ITC considering the small signal stability constraints.Finally,an ambient data-driven ITC online evaluation method considering small signal stability constraints is proposed.Furthermore,the difference between the ITC evaluation result and the current interarea transmission power is used to determine the precise modulation adjustment in generation rescheduling strategy.(4)Facing the problems of expansion of modern power systems,flexible operating conditions and insufficient damping modulation basis,an online method of ambient data-driven participation factor(PF)with respect to generator active output based on Rsub-DMD is presented.The proposed PF index quantitatively analyze the correlation between electromechanical mode and generation outputs to accurately select the generator sets for rescheduling.Moreover,based on the estimation of total active power adjustment determined by ITC evaluation result,combining with the PF identification results,the optimal allocation scheme of the number of modulation units and the corresponding amount of generator participating in active power modulation is given.With the determination of modulation location and amount of generation modulation,ambient data-driven damping modulation strategy based on precise generation active power modulation can be built,and online damping enhancement for interconnected power systems is achieved.