Study of a coherency-based simple dynamic equivalent for transient stability assessment

Earlier, a simple dynamic equivalent for a power system external area containing a group of coherent generators was proposed in the literature. In the proposed method, all the coherent generators are first decomposed into smaller generators. This is a new concept. The smaller generators are then aggregated in two levels. In this study, a new alternative and much more justified approach is proposed for the first-level aggregation. However, for the second-level aggregation, the same earlier approach is used. The resulting dynamic equivalent has a power system structure. In online applications, this equivalent does not require any measurement data from the external area. Very recently, the performance of the dynamic equivalent has been extensively investigated on the New England 39-bus 10-generator system, the IEEE 162-bus 17-generator system and the IEEE 145-bus 50-generator system. The results of this investigation are presented here for a complete validation of the proposed method.