Research On Unstable Mode And Splitting Strategy Based On Transient Energy Function

For many years, a good result has been obtained by using the splitting strategy based on ideal two-group instable mode. However, with the construction of AC / DC power grid in China, the operation mode and fault mode are becoming more and more complex, resulting in new problems and challenges in safety and stability of power system. Both the practical experience and simulation results demonstrate the fact that the subsystem loses stability fast after the splitting of the original system. Therefore, the research is urgent and demanding to find the way to classify unstable modes and propose splitting strategies under multi-group oscillation.Compared with multi-group instable phenomenon, successive instable phenomenon is more common in power system. The lack of analytical method is a serious problem to analyze multi-group oscillation. Since the motion of the multi machine system under large disturbance can be divided into the relative motion between clusters and the relative motion in clusters, the concept of transient energy between clusters and transient energy within clusters can be put forward. The time of out-of-step(tm) can be acquired based on the characteristic of transient energy between clusters of original system and CCEBC. By analyzing the characteristic of the transient energy between clusters of subsystem, the critical clearing time(tn) can be acquired. The unstable modes can be classified into successive-instable mode, strict multi-group mode and lax multi-group mode by comparing the length of tm, tn and tc(fault clearing time).when the unstable mode is successive-instable mode or lax multi-group mode, the subsystem will lose stability by using traditional splitting strategy, which can easily cause large area blackout. Therefore, new splitting strategies are provided for different instable modes in this paper, which is of significance to the stability of subsystems under multi-group oscillation. When the unstable mode was successive-instable mode, using the passive splitting strategy to split the out-of-step power system during tm to tn will keep the subsystem stable. When the unstable mode was lax multi-group mode, the usage of the active splitting strategy to split the out-of-step power system before tn will keep the subsystem stable. However, when the unstable mode was strict multi-group mode, the out-of-step power system can be only splitted into multi groups.The validity of the previous analysis has been testified through simulation verification of actual power grid model and 10-machine IEEE test system.