Optimal re-dispatch of generating units ensuring small signal stability

This study presents a new re-scheduling method for generating units in the form of optimal power flow (OPF) problem, considering small signal stability (SSS) constraint of power system in normal operation andN-1 contingency of transmission lines outage. In base case, total operation cost is minimized, considering voltage stability margin andN-1 line contingency. The SSS of system is studied by using modal analysis. In case of unstable modes in the generator(s) rotor angle, the generators scheduling should be re-dispatched. Using modal analysis and sensitivity matrix, the generators are divided into three groups: increasing power generators, decreasing power generators, and unchanged power generators. In order to increase the accuracy of re-scheduling program, two new technical and economic indexes are introduced. The output power of the candidate generators is increased/decreased based on the indexes to stabilize generator(s) with unstable rotor angle (URA). The salient feature of proposed method is its capability on stabilizing system with one or more URA generators with minimum changes in base case OPF results. The Validity of proposed method is studied on IEEE 39-bus 10-machine, and IEEE 69-bus 16-machine test systems. The obtained results verify effectiveness of proposed re-dispatch algorithm in case of single or multiple URA generator(s).