Linyan Cheng

Study on security protection of transmission section to prevent cascading tripping and its key technologies

Cascading overload trip due to lack of transmission section protection is an important reason of large-scale blackout. This paper illustrates the meaning of transmission section and points out that the objective of transmission security protection is to maintain its integrality and transmission capacity, and to avoid cascading overload trip. In addition, the implement condition and key technology are discussed, which are online capture of transmission section, real-time prediction of cascading overload and real-time emergency control to avoid cascading trip. This paper has brought forward the primary scheme. Its validity is verified by the calculation result of CEPRI 36 test system and a province system.

A Novel Fast Searching Algorithm for Power System Self-Adaptive Islanding

Self-adaptive system islanding refers to the separation of an interconnected power system into electrically isolated islands automatically based on the identification of unstable mode. A fast searching algorithm for self-adaptive power system islanding, which is called multilevel reduced graph partitioning (MLRGP) algorithm, is presented in this paper. The aim of this algorithm is that the generation load imbalance in each island is as small as possible. The algorithm computes a reasonable islanding strategy of power system G=(V, E) in O(|E|) time. A C++ program is developed based on the algorithm. The verification of the islanding program is proven with simulations on a practical 212-bus power system. It costs only about 20 ms to get a reasonable islanding strategy on an ordinary PC, which satisfies the speed demand of self-adaptive system islanding.

Fast search for transmission section based on power component of line

This paper proposes an algorithm fast searching for key transmission section based on power component of line. Firstly, graph theory is used to calculate the real power transfer among individual generators and loads, then classify the lines based on the Wards cluster analysis method to search the set of lines which have the similar power component to overload line, finally determine the parallel transmission section of the line according to the direction of the overload line and the set lines. As a result, the works of further calculation and security analysis can be reduced greatly. And fast security protection of key sections to prevent cascading tripping can be achieved accordingly. At last, the validity of proposed algorithm is verified by the calculation result of IEEE 14 test system.

Study on the coordinated voltage control with the distributed model prediction

This paper mainly study on the coordinated voltage control scheme with model predictive control (MPC). As the decomposition-coordination technology and the auxiliary problem principle is employed into the MPC based voltage control problem, a distributed voltage control model and structure can be obtained, and the global centralized optimization problem is decomposed into some sub-problems. All sub-problems are only related to their local model and data, and can be solved in a distributed manner, which is benefit to reduce the dimension of the optimization problem and improve the flexibility of control and calculation. Simulations conducted on typical power networks indicate that this voltage control scheme can prevent the voltage instability effectively and the distributed MPC scheme can obtain similar control performance to the centralized MPC scheme.

Stability control of power system integration of VSCF wind generator

To improve the stability of the power system integrated of wind farm, the wind power system energy function is proposed in this paper based on the energy conservation law. Then a stability control strategy based on the energy function is introduced. The impacts of DFIG operation limits on the control effect are also discussed. By variable speed operation, the control strategy restrains the wind power system oscillations by eliminating the system unbalancing energy during the disturbances. In the simulation study, a testing system including a DFIG based wind farm which is implemented in DIgSILENT/Power Factory is conducted to demonstrate the effectiveness of this strategy. The simulation results show that, in different system operation statuses, the control strategy is effective in improving the power system synchronous stability without deteriorating the system voltage stability.

Study on closed-loop transient stability emergency control based on wide area measurement

In this paper, a method, which is essential in initiating emergency control measures, is proposed for fast and accurate online detection of transient instability based on real-time measurement. Under a certain disturbance, the candidate critical cluster of power system is predicted and refreshed at each sampling step. The method identifies the loss of synchronism at each time step by observing the geometric characteristic of the post-fault trajectory of the generalized one-machine equivalent system. A new structure of the emergency control scheme relies on SIME (for Single Machine Equivalent). It is unnecessary to calculate the unstable equilibrium point and some limitations caused by the time-invariant assumption are also eliminated. Simulations are carried out on the IEEE 50 generator test system and a real power system. The results indicate that the proposed method has the features of reliability and effectiveness in preventing the system from the loss of synchronism.

Study on Fast Control Algorithm Based on Integrative Sensitivity Analysis

If the trip of overload branch may cause cascading tripping in corresponding section, emergency overload control should be executed to ensure the security of the transmission section and maintain its integrality and transmission capacity. A series of improvements against the conventional sensitivity algorithm are proposed, which include the advance of the integrative sensitivity, the use of equal and opposite quantities in pairs analysis method, and the introduction of heuristic rules. The choice of control node and its quantity ensures that the power flow of overload branch won’t arise and normal branch won’t overload, so the control strategy can availably and quickly eliminate overload. The rapidity and validity of proposed algorithm is verified by a lot of calculation results of a certain real system. Keywords-transmission section;integrative sensitivity; heuristic rules; equal and opposite quantities in pairs

Doubly Fed Induction Wind Generator Model and Its Operation Investigation

A Doubly-Fed Induction (DFIG) wind generator dynamic model is developed in PSCAD. Then a novel active power control strategy based on the indirect speed control is introduced to implement the power control tasks and the limits of these controls are also discussed. The novel strategy ensures that wind power generators without wind speed measurement can achieve the balance control and maximum power tracking to perform active power control tasks constrained by the available wind. In the simulation study, a single-machine infinite bus system with a wind turbine rated at 2 MW is conducted to demonstrate the behaviors of the generator in both steady state and transient state. The simulation results show a good performance of the dynamic model and the effectiveness of the control strategies.