Qing Fen Liao

Study on Electrical Parameter Frequency of the Out-of-Step Oscillation Center

Out-of-step splitting is an emergency strategy to trigger splitting devices to separate power systems into several sub-regions through capturing oscillation center before the collapse of the system. How to position the oscillation center rapidly and accurately is a key procedure in out-of-step splitting field. This paper proposes a new method to position the oscillation center based on electrical parameter frequency. Firstly the current and voltage frequency variation characteristic of out-of-step tie line is analyzed. Secondly, the electrical parameter frequency variation rules are summarizes, i.e. curves of buses voltage frequency of the oscillation center line change continuously without intersection and they have the opposite variation trend. At last, the oscillation center can be positioned accurately within half out-of-step cycle by constantly monitoring electrical parameter frequency of the transmission tie lines. The accuracy and rapidity of the method are certified by the simulation results of four machine two regional power system.

Study on a Controlled Splitting Scheme Based on Layer Expanding Graph Algorithm

Optimal controlled splitting is an emergency strategy to split the power system into several sub-regions based on global electrical information before the collapse of the system which is subject to severe disturbances. How to seek the optimal splitting sections rapidly and accurately is a key problem in controlled splitting field. A controlled splitting scheme based on layer expanding graph algorithm is presented in this paper. Firstly, source nodes of island regions extend out for the formation of the island regions. Secondly, island regions can be combined to make up synchronous sub-regions on the basis of the clustering of generators. At last, the optimal sections can be determined according to the initial and improved adjustment of splitting sections. Moreover, the scheme proposed can be adapt to the change of operation mode of the power system. The accuracy and effectiveness of the scheme is shown by the simulation results of CEPRI 36-bus system.

A Method of Controlled Islanding Strategy Based on Artificial Fish Swarm Algorithm

Optimal controlled islanding strategy searching is a complex combinational optimization problem. Artificial fish swarm algorithm (AFSA) based on the simulation of fish swarm is an intelligent meta-heuristics. In this paper, AFSA is applied to the searching of optimal controlled islanding strategy. In order to minimize the unbalanced power in each island, a mathematic model is established with some constraints. Simulation result on IEEE-39 node system shows that the proposed method can obtain the optimal strategy promptly and has strong global search ability.

Fast Computation of Sample Entropy in Forced Oscillation Detection

Forced power oscillation in power systems has a serious influence to the safe and stable operation of power systems. A fast dynamic sample entropy algorithm is proposed based on sample entropy in this paper. The change of dynamic sample entropy of the tie-line power is analyzed to determine whether the forced power oscillation happened. Case study on the 4-machine 2-area system shows the effectiveness and efficiency of the proposed methodology.

Distinction of the Property of Low Frequency Oscillation Based on ARMA Mode Identification

Aiming at how to solve the question of quantitatively distinguish negative damping low frequency oscillation and forced power oscillation, the difference in frequency and damping ratio between the two kinds of oscillations have been discovered through mechanism analysis, and a new quantitative distinction criterion for the property of the low frequency is proposed. The oscillation data is windowing identified by ARMA model based on weighted recursive least squares algorithm dynamically, and low frequency type can be distinguished according to the changes of oscillation frequency and damping ratio during the oscillation. The simulative results have shown that the method is feasible and effective.

Early Warning of Low Frequency Oscillation and Analysis of its Related Issues

This paper set up the model of power transmissive observational section and put forward the real-time tracking method of power angle curve in steady state which could be used to identify and focus on monitoring the weak links, then to take early warnings of low frequency oscillation. On the dynamic situation of system been disturbed, we extracted the real-time dynamic damping value of the observational section, calculated its fitting curve of local maximum points and took the slope of curve as the criteria, in order to achieve early warning of low frequency oscillation under multiple disturbances in the interconnected power system.

Gobal Optimization Based Power System Stablization with WAMS Time Delay Study

It is very important to take into consideration time delay in wide area power system stability; the design of PSS (Power System Stabilizer) should consider global optimization with WAMS (Wide Area Measurement System) time delay. Newly designed PSS should be insensitive to time delay and suppress internal low frequency oscillations. It is used as feedback signal and is real-time synchronous that WAMS signal shows. Power system is modeled with the consideration of time delay. LMI (Linear Matrix Inequalities) is used to solve the stability condition of time delay system. Based on the time-delay effect of the wide-area measurement signals, this paper redesigned the PSS with global optimization of power system. The attached two-area-four-machine system simulation illustrates that wide-area PSS designed by global optimization with the consideration of time-delay can limit internal low frequency oscillation with time-delay insensitivity, and improve the stability of power system. It implements global optimization of PSS with WAMS time delay stability.