Research On Control Strategy Of Power System Out-of-step Splitting

The construction of the large-scale interconnected power grids has become an inevitable trend at home and abroad.At the same time,the safety and stability problems of the power system are also more urgent.As the last defense,the out-of step splitting control can prevent from the widespread outages under the complex fault accident,and it plays an important role in the domestic power system.Firstly,using a two-machine equivalent system model,the mechanism of power system out-of-step oscillating center migration is studied.The influence factors of the migration of oscillation center are analyzed and summarized,such as the instability mode change,the system impedance change,impedance irregularity and potential amplitude inequality.Then,the migration mechanism of the oscillation center is studied considering both impedance irregularity and potential amplitude inequality.The analysis show that oscillation mode alternating and impedance changing may cause the oscillation center to migrate discontinuously,while potential amplitude inequality and impedance inequality may cause the oscillation center to migrate continuously.Secondly,considering the influence of the oscillation center drift,a new splitting strategy is proposed based on wide-area information.Using a two-machine equivalent system model,the location of out-of-step center and the migration mechanism of oscillation center are studied considering both impedance irregularity and potential amplitude inequality.The potential lines which contain the oscillation center are filtered by the minimum voltage.The position function and potential amplitudes ratio of the equivalent systems at two sides are defined,the calculation method of the position and voltage of oscillation center is derived,and an out-of-step criterion based on voltage variation of oscillation center is presented.The final splitting surfaces are determined by synthesizing the drifting characteristics of oscillation center and the degree of unbalancedness of the post-splitting islands.Simulation results of IEEE 9-bus system verify the validity of the analysis and the effectiveness of the proposed strategy.Finally,a splitting section search optimization method is put forward based on the identification of coherent generators,the method can be divided into three stages: building power system graph theory model,initial section search based on the current tracking algorithm and final solution based on adjacent nodes transform column cross-section optimization.Among them,the initial dissection of the algorithm based on the trend tracking algorithm is limited to a smaller area,which greatly reduces the search space of the column section.Based on the initial section,the ultimate solution column optimization can quickly reduce the unbalance degree of the isolated islands,which based on the transformation of adjacent nodes,and achieve the rapid optimization of the solution column effect.This method solves the problem of the combination explosion and fast speed of the search space in the traditional unlisted section search.The effectiveness of the method was validated by the IEEE10 system 39 node system.