Research On Real-time Transient Stability Assessment And Emergency Control Of Power System Based On Wide-Area Response

The development of large-area interconnected power systems and the large-scale intermittent energy access have advanced further requirements for stability and security control system of power system,and transient stability control mode is getting into real-time decision and real-time control gradually.The security and stability control technology based on WAMS(wide area measurement system)overcomes the problems of the traditional transient stability analysis and control pattern which is difficult to meet the real-time requirements.It can achieve real-time decision and real-time control and has received widespread attention from domestic and international scholars.For the three key problems of transient stability control research including the transient stability post-fault trajectory prediction,transient stability assessment and transient stability emergency control,the transient stability analysis and control technology based on wide-area response information is studied.This paper is mainly as follows:(1)For post-fault trajectory prediction of transient stability,a real-time post-fault trajectory prediction method based on self-memory grey Verhulst model is provided.Taking full consideration of the typical dynamic characteristics and the strong nonlinearity as well as the random fluctuation of transient stability post-fault trajectory,the self-memory grey Verhulst model is established based on grey Verhulst model.After that,a real-time model-parameter-adaptive prediction scheme is presented,in which the equal dimension and new information data model as well as the rolling prediction method are adopted to improve adaptability and adaptivity of prediction by updating sampling data continually and making full use of real-time measurement data from WAMS.Furthermore,combined with equal area criterion,the proposed prediction scheme is conducted to detect transient instability,and simulation results indicate that the proposed prediction scheme is effective for prediction of transient stability.(2)A model-free transient stability on-line analysis method based on the stability criterion theory of the largest Lyapunov exponent(LLE)in nonlinear dynamic system is studied.Firstly,the problem of transient rotor angle stability is depicted from the viewpoint of nonlinear dynamic system,and the research idea of transient stability problems based the LLE is established according to the stability criterion of the LLE.The improved LLE estimation method based on the direct estimation method principle,and the dynamic characteristics and the key feature of the LLE of the relative rotor angle response trajectory are analyzed.After that,the transient stability monitoring method and coherent groups identification method basd on the LLE dynamic characteristics of response trajectory are proposed respectively.For the problem of incomplete PMU placement,the former provides an on-line transient stability monitoring scheme based on the critical generator pair to weaken the requirement of PMU placement and reduce computational cost.For the critical machines cluster identification research,the latter provides an on-line critical machines cluster identification method based on the LLE.The proposed approach is purely data-driven and the computation is simple and fast,and it is easy to realize on-line transient stability anlysis.The proposed approach serves as the foundation for later researches on transient stability assessment and emergency control.(3)For transient stability assessment,a transient stability assessment approach based on the LLE and rotor speed is presented.Firstly,through establishing a mathematical model that accounts for the LLE value obtained by a model-free algorithm and the rotor speed,as well as using dynamic characteristics of post-fault phase-plane trajectory and the key feature of the LLE of response trajectory,a fast stability criterion based on the LLE and rotor speed is proposed.Furthermore,a real-time transient stability assessment scheme based on the critical generator pair is provided to weaken the requirement of PMU placement and maked the assessment faster.For the proposed approach combines the stability principle of non-linear dynamical system with the physical mechanism of transient response,it can ensure the assessment accuracy and rapidity.Compared with the conventional LLE method,the proposed method does not need a predefined optimal time window and does not need a large time calculation for the LLE-time curves to monitor the final signs of the LLE and can gives the exact stability assessment time.Besides,compared with the general phase-plane trajectory method,the proposed method will not be affected by the irregular changes and mutations of the phase-plane trajectory,and it can always provide a reliable assessment.(4)For transient stability emergency control,a closed-loop emergency control method by combining generator tripping and load shedding is proposed.Firstly,the unbalanced transient energy function of power system is defined based on motion equations of generator,its property is analyzed based on the definition and conservation after fault of the corrected energy function.And by combining the unbalanced power characteristics for power system in steady state operation condition,the calculation method of the control quantity of generator tripping and load shedding is obtained.Since the proposed method is based on the essences of transient instability,the accurate control quantity can be obtained.Besides,the low frequency or low voltage problem of system caused by single generator tripping control can be improved effectively by the proposed combined generator tripping and load shedding of emergency control method.Finally,integrating the paper method of full text,a whole real-time closed loop emergency control scheme based on the real-time measurement information obtained from WAMS is proposed.The proposed method can predict transient instability in advance by combining the transient stability post-fault trajectory prediction with the fast-transient stability criterion,and then take emergent control as soon as as soon as possible by using the proposed closed-loop emergency control method to keep the security and stability operation of power systems.