Reserch On Response-Based Power System Transient Stability Control Technique

The security and stability of power system is significant to the national economic development and social stability, which attract more attentions from academics and industries in the world. In these years some serious blackouts occurred which have caused huge economic losses, and revealed that the traditional stability control system cannot handle the contingency with low probability. Compared with the traditional method, the response-based control is free from the influence of power system component models and parameters with no requirement to making planned operational mode and contingency set. It can comprehensively and objectively evaluate power system security and stability level and provide appropriate control measures to prevent blackouts. Thus, the response-based power system real-time transient stability identification and control strategy is mainly studied in this dissertation, which mainly includes:(1) Firstly, an identification method based on the variation trend of rotor speed difference-rotor angle difference is proposed to estimate the power system transient angle stability based on response. According to the characteristics that the power system often behaves as the two-group instability mode and based on the variation characteristics of the motion trajectory on the phase plane, whether the two machine groups can keep synchronization in the transient process will be estimated by this method. In order to overcome the defect that the trajectory of the virtual equivalent inertia center is unsmooth, the least square method is adopted to judge the trajectory tendency and the system transient angle stability. This method only needs the response information of generator’s power angle and speed. It is convenient and fast, which can be used as starting criterion of transient stability emergency control. Finally the effectiveness of the proposed method is verified by simulation.(2) In the aspect of response-based power system transient stability real-time emergency control, an emergency control scheme based on the relative kinetic energy is proposed. The transient stability identification result estimated from (1) is used as the starting criterion; the capability of the two-machine system absorbing transient energy is evaluated by relative kinetic energy. The machine tripping amount is calculated according to the equal area criterion to form a complete closed-loop real-time emergency control scheme. In order to take into account the impact of the time delay of the emergency control, the delay time is considered in the control strategy to enhance the accuracy. This method only depends on the system dynamic response curves, is free from the influence of power system component models and parameters, and doesn’t need to preset operational mode and contingency set. Thus it is suited to complex operational modes and contingency types. Finally the effectiveness of the proposed method is verified by simulation, showing that the proposed scheme can prevent the system from further deteriorating and even widespread blackout.(3) In order to comprehensively defend power system transient voltage instability and transient angle instability, a new comprehensive real-time emergency control scheme based on the transient angle stability real-time emergency control scheme is proposed. A transient voltage instability real-time identification method is developed, and a load shedding control scheme is proposed. These two stability problems have the same time scale, so it is difficult to identify voltage instability or angle instability from the variation of voltage and angle in the unstable process. The parallel judging method is applied to monitor both system voltage and angle stability problems. When it is detected that the system will be unstable, a corresponding emergency control measure is implemented to enhance the system stability. Finally the effectiveness of the proposed method is verified by simulation, showing that the proposed method can correctly detect the key factors influencing system stability and can implement corresponding measures. The power system transient stability real-time emergency control scheme can be enriched, and the system voltage stability can be introduced into the comprehensive defense system, solving the main problems of power systems.(4) Based on the new characteristics discovered in the simulation analysis of interconnected power systems in our country, the phenomenon of interconnected power system instability caused by fault occurred in the remote end of regional power grid and the key factors influencing the interconnected power system stability characteristics is studied. It shows that both the network topology and the operational mode can influence the transient instability mode of interconnected power systems. The impact of angle swing between machine groups in the regional power grid on the transient stability is mainly studied. This paper provides new transient stability characteristics of interconnected power systems through the point of the impact of machine group angle swing on the equivalent potential in the regional grid. The analysis indicates that the post-disturbance angle swing between generator groups in the regional grid can affect the amplitude of equivalent potential, which lead to variation of transient stability of interconnected systems and influence the capability of system transient stability. The conclusions are verified by the simulation to the actual power grid. The work in this paper contributes the mastery of transient stability characteristics of large-region interconnected power systems, and the mining of operation characteristics of large-region interconnected power systems.