Identification of vulnerable lines in complex power system can effectively prevent large-scale cascading failures, which may lead to power system collapse. In order to identify vulnerable lines quickly and accurately, the physical properties of transmission lines are considered while building the correlation of each transmission line of grid. The hyperlink-induced topic search (HITS) algorithm is used to quickly obtain the vulnerable lines of large-scale power grid. Combined with the characteristics of the algorithm, the importance index of transmission line is obtained, which indicates the influence of some line fault on the other lines. The experiments are carried out on the IEEE-39 bus system and IEEE 118 bus system to verify the effectiveness of the proposed method in the cascading failure identification of power system, which also shows the capability to assess the transmission line vulnerability in only a few seconds.

Transient voltage instability and transient power angle instability are two main modes in transient stability analysis of power system, whose relationship is very comprehensive. Based on the analysis principle of Lyapunov direct method, a new index to identify the transient instability is proposed in this paper. The proposed index is established according to the extension of the network structure preserving model. In this paper, the structure preserving model of transient energy function is further extended to build the transient energy relation functions, which are not only the energy change projected into the index as a basis, but also comprehensive consideration of voltage instability and power angle instability characteristics. At the same time, this paper combines the method of trajectory analysis and refers to the change of the transient relationship functions to realize the control of the transient instability of the system. Simulation studies on the IEEE New England power system are carried out to verify the effectiveness of the proposed recognition method of transient instability modes for transient power angle instability and transient voltage instability.

The time evolution stochastic dynamics (TESD) and the unexpected stochastic event driven (USED) are significantly increased to change the dynamic characteristics of the power system operation. In this paper, a new algebraic differential model for the doubly-fed-induction generator (DFIG) in the wind farm is constructed to reflect the stochasticity of the TESD and the USED in the power system more intuitively, which is based on the Lyapunov transient stability theory and the noise to state stable (NSS) control theory. Sequentially, a new torque stochastic robust controller (TSRC) model construction method is proposed to apply more reliable and effective control to weaken the influence of the stochasticity on the whole system and reduce the pressure on the collaborative control of the power system in case of the stochastic large-scale system failure. This model shows that the wind farm system with the torque stochastic robust controller has higher robustness. Finally, a simulation of the New England 9-bus system with the DFIG is conducted to verify the applicability of the algebraic differential model in a deterministic system and the results show its potential application for the robust controller considering the power system with the wind farm.

With a large number of renewable energy connected, the penetration rate of grid connected inverter increases rapidly, and the interaction between converter and power grid and between converter and converter becomes more and more intense. The assumption that power grid is regarded as infinite power supply is no longer tenable. And a large number of new energy resource will change the transient instability mode of the power system and increase the risk of security and stability. In the process of simulation, how to establish a reduced order aggregate equivalent model of converter suitable for transient stability simulation becomes an urgent problem to be solved in the research of new energy resource connected. In this paper, based on singular perturbation theory, the reduced order modeling of DFIG (Doubly fed induction generator) converter is carried out. Firstly, according to the typical triggering criteria of DFIG relay protection action in transient stability problem, the modeling principles of relay protection and low voltage ride through behavior are analyzed, so as to accurately simulate the transient instability behavior of generator tripping. Secondly, a combined system of synchronous generator and DFIG wind turbine model is built. Different instability modes are classified by the time period and time scale of instability, and the influence of DFIG power supply on grid voltage instability is analyzed.

A large number of renewable generation through the power electronic interface and synchronous ac system by the full coupling and partial coupling, will change the transient instability mode of the system and increase the risk of security and stability. In the system-level simulation, how to model and equivalently aggregate the power electronic interface power supply and analyze the transient stability of the power system with the power supply by a large number of power electronic interface becomes difficult. Based on the hybrid automata theory, the operation process model of the power electronic system has been established. The interface selects the NPC(Neutral point-Clamped) three-level converter which is widely used in the field of medium voltage and high. The mixed relationship between discrete events and continuous events is derived in detail. The power characteristics of this kind of power supply are explained according to the unique principle of the electromechanical coupling. According to the principle of the electromechanical decoupling characteristic of power electronic interface, singular perturbation power is analyzed and a DAE(Differential Algebraic equation) reduced order model of power electronic interface is established. Then, the effectiveness of the reduced-order model is verified under the conditions of different external disturbances on the grid side and the internal parameter configuration of the power supply. The simulation results show that the model can not only reveal the transient instability mode of power electronic and maintain the simulation accuracy of the external characteristics of power supply, but also obtain the transient instability time accurately. Furthermore, the model has good transient stability characteristics.

Due to the non-linear operating characteristics of wind turbines generation (WTG), traditional control methods cannot give full play to their ability to response the system frequency, resulting in poorer frequency characteristics of the system after wind power is connected to the grid. Therefore, this paper proposes a coordinated control method for wind farms. At the wind farm level, a method for grouping control of wind turbines under different wind speeds is proposed. Different WTGs use different load reduction coefficients, which improves the stability of wind turbines and avoids the second drop in frequency. At the level of WTGs, the equivalent inertial time constant of the wind turbine is calculated, which provides a theoretical basis for the control method. A controller based on adaptive fuzzy control is designed, which dynamically changes the control coefficient in different stages of frequency response, improves the active output of wind turbines participating in the inertial frequency modulation stage, and reduces the static error of primary frequency modulation. The simulation model of the proposed control strategy was applied to simulate different frequency fluctuations. The results show that the frequency response of the WTG after grid connection is significantly improved, proving the effectiveness and robustness of the proposed method.