Studies On Boundary Features Of Power System Dynamic Security Region

In the trend of modern interconnected bulk power systems, how to analyze transient stability and dynamic security problems is an extremely important task for power system planning and operation. A dynamic security region (DSR) that is defined in injection space is unique for a specific configuration and a given fault. The security of the operation point can be determined only by simply judging whether the current injection lies in the DSR. Moreover, according to the relative distance between the operating point and the boundary of DSR, the index of security margin and security transition probabilities can be determined. DSR has extensive on-line application prospect since it can provide more security information and is more suitable for security monitoring, assessment, control and pricing. On the basis of the formers' work, some global and practical boundary features of DSR are studied and some conclusions are obtained as follows:1. Based on lots of simulations, this paper validates the following two global boundary features of DSR: (1) the boundary of DSR is close whether considering the limits of node injections or not, and (2) the original point is always inside DSR. Then, three practical boundary features of DSR are proposed. These facts and features have been evaluated on the 10-generator, 39-bus New England Test System by 2-dimension section of the DSR.2. Based on formers' research about coherency identification using Reachability Grammiam, this paper introduces K-medoids algorithm to coherency identification, and avoids the iterative computation generated by using Reachability Grammiam. At the same time, a new method of identifying instability modes near normal operating point is proposed. This method is based on the approximate invariance of Reachability Grammiam on injections of different operating points near normal operating point and identifies instability modes quickly at the normal operating point instead of the critical operating point. A program about identifying instability modes has been developed and the method has been evaluated on the 10-generator, 39-bus New England Test System and IEEE 17-generator, 162-bus Test System. Using the result of identifying instability modes, a new strategy of search critical operating point is proposed. Owing to its low search scale, this strategy can get some critical operating points quickly, which represent certain instability mode. The speed and accuracy of the direct method determining the practical DSR can be improved by using this strategy.