A new method was proposed to adjust the power of the section with transient stability constraints. Using the sensitivity of transient stability margin based on phase-plane trajectory concavity-convexity to a change in generator active power, transient stability constraints were converted to generator active power constraints. Combined with the sensitivity of section power to a change in generator active power, section power can be expressed by linear superposition of generator active power. Thus, the linear programming model can be established for section power adjustment with the transient stability constraints, and the adjustment procedure was given. According to the desired value of transient stability margin, the generator output and corresponding section power can be determined. The simulation results in the IEEE 39 system validate the effectiveness and feasibility of the proposed method.

Transient stability assessment (TSA) of the power system is essential to the safe operation of the power grid. The TSA of the multi-area interconnected power system is a challenging task due to its special multi-area power grid structure. New features, which are the time-variable instability mode and untypical two-group instability mode, emerge in the transients of the interconnected power system and affect the accuracy of conventional TSA methods. To address these problems, we propose a novel TSA method based on the modified equivalent single machine infinite bus (ME-SMIB) system. Two key technologies, namely generator groups identification and generator selection, were presented in the proposed method. Generator groups were identified at each time-step to track the time-variable instability mode. Two groups of generators that were of good coherency and closely related to the current instability mode were selected to construct the ME-SMIB system. The transient instability was finally identified by the concave-convexity-based method. The proposed method was tested in the 16-generator 68-bus power system and China interconnected power system. Results show that the proposed ME-SMIB system can avoid the misjudgments caused by new transient features of the multi-area interconnected power system, presenting superior reliability than the conventional E-SMIB system.

The transient instability identification and control based on the convexity and concavity of phase trajectory is a new method in recent years,which is expected to be applied in the emergency control of power system based on the PMU information.The key technical steps of real-time generator grouping and the necessity of correct use of segmented phase trajectory are emphasized when this method is applied to multimachine power system.In addition,some misunderstandings about its applications reported in related references are analyzed and the matters needing attention for the further comprehension and application of this method are deeply elaborated.

Time-domain simulation (TDS) for power system transient stability is inefficient and tedious,and it can't provide quantitatively stability margin.This paper proposed a novel TDS termination algorithm based on phase-plane trajectory convexity-concavity.After further analysis of phase-plane trajectory motion characteristics,the transient stability margin is defined based on phase-plane trajectory convexity-concavity.Combined with the traditional time-domain simulation,the stability of following trajectory can be evaluated according to the obtained trajectory information based on the proposed stability margin.The simulation can be terminated if the system is detected to be long-term stable and unstable,otherwise,the simulation should be continued until the termination criterion is satisfied.The proposed algorithm can improve off-line transient stability analysis of practical engineering,its efficiency and validity is verified by simulation results on IEEE 39-bus 10-unit system.

提出了一种基于轨迹凹凸性理论的暂态稳定切机控制策略表整定方法,该方法能够有效提高策略表整定过程的效率,避免了大量的重复性仿真工作.针对会给系统带来重大冲击的预想故障,基于时域仿真结果,可以得到系统的暂态功角稳定性;当系统发生暂态失稳时,根据不稳定事故的仿真信息,得到控制时刻和不稳定平衡点处的功角以及控制时刻的角速度,可以计算出较准确的控制量.实际电网系统的仿真结果验证了所提整定方法的快速性.

A novel method for power system first-swing transient stability fast detection is proposed in this paper. Based on the convexity and concavity of phase-plane trajectory, motion characteristic of phase-plane trajectory is further studied, and a novel criterion for first-swing transient stability detection is proposed. The stability can be detected before the trajectory reaches its Farthest Point (FEP), and instability can be detected before the trajectory passes through the Dynamic Saddle Point (DSP). The efficiency and validity is verified by simulation results on OMIB system and IEEE 39-bus 10-unit system.

A combined emergency control strategy of generator tripping and load shedding was proposed. When power system subjected to disturbances loses synchronization, the strategy can prevent system instability and also improve the frequency and voltage. By analyzing the characteristic of the phase-plane trajectory representation of power angle and rotor speed, the relationship between the unbalanced power and the slope of the trajectory is obtained. Based on the kinematic equation of the rotor, the expression of the relationship between the unbalanced power and the slope is deduced and the control algorithm is derived. And then, the start-up condition of the combined control strategy is presented and the allocation algorithm of generator tripping and load shedding is given. The simulation results in IEEE 39-bus system and the Sanhua system validate the effectiveness of the combined control strategy.

This paper addresses the issue in critical machines identification for real-time assessment and control of power system transient stability. To satisfy both accuracy and rapidity, on the basis of clustering study on a 3-unit 9-bus system, a novel real-time critical machines identification method is proposed. First, three candidate decomposition patterns are selected by the top three largest predicted angle variation distance; And then an index is proposed to choose the pattern whose equivalent OMIB system operating state goes farthest from the equilibrium point as the best decomposition pattern. The scheme only needs real-time machine dynamic information, and has the advantage of little computation, rapid identification speed and excellent accuracy. Simulations on IEEE 39-bus 10-unit system validate the efficiency of proposed scheme.

Critical machine identification is of primary importance for online transient stability analysis and emergency control. In this paper, a novel real-time critical cluster identification scheme using WAMS information is proposed. First, the candidate clustering modes are obtained by the relative big angle gaps. Second, choose the clustering mode which gets the maximum equal angle after single-machine transform as the correct cluster mode which can be used to analyze the transient stability. The scheme has the advantage of little computation, fast identification speed and high accuracy according to the simulation results on IEEE standard 39-bus 10-unit system.

Fast and accurate coherency identification is necessary for the equivalence transform when real-time analyzing the transient stability of power system. In this paper, a novel method of coherency identification based on Wide Area Measurement (WAMS) is presented. By analyzing the dynamic process of the system, a comprehensive variable is obtained by giving angle, angular velocity and angular acceleration time-varying weights to better reflect the difference of real-time dynamic behavior among generators. Thus, the coherency identification method based on comprehensive variable is put forward. Besides, an evaluation method based on Davies-Bouldin's Index (DBI) is presented to real-time assess the rationality of clustering result. The speed and accuracy of the proposed scheme is verified by simulations on IEEE standard 39-bus 10-unit system.

Time-domain simulation (TDS) for power system transient stability is less efficient and tedious, and there is no uniform standard to determine the transient stability based on empirically observation of the disturbed trajectories, which make the efficiency and reliability cannot be satisfied at the same time. A novel termination algorithm of time-domain simulation for transient stability analysis based on phase-plane trajectory geometrical characteristic is proposed in this paper. The output of time-domain simulation is used to analysis the transient stability, and once the system is judged to be stable or unstable, the time-domain simulation program is terminated. First, the transient instability can be detected quickly based on the convexity and concavity of phase trajectory; and if the phase trajectory is convergent and the oscillation is damped, the system can be detected to be stable early. The proposed method is easy to achieve, the efficiency and validity is verified by simulations on IEEE 39-bus 10-unit system.

With the fast development of WAMS system, we can obtain the real-time information of power system, which makes it possible to realize the real-time transient stability analysis and close-loop control. The coherent generators identification plays an important role in the transient stability analysis on power system. It is the first step to study the stability of a multi-machine power system. So research on a coherent generators identification scheme based on the real-time information is necessary and vital important. This paper proposes an identification scheme of coherent generators which can be applied online based on the WAMS information. The scheme has advantages of little computation, fast identification speed and high accuracy. Besides, a coherency index is also proposed to evaluate the clustering result. The simulation on IEEE standard 39-bus-10-unit system verifies the speed and accuracy of the scheme.