Coherency based equivalents for long-term dynamic studies

Abstract

Dynamic equivalents are reduced order differential equation models of the dynamic characteristics of a power system. The reduced order model is formed by lumping together group of power plant units (coherent group) which ends to swing together for a given perturbation. Each power plant unit is represented as constituted by a synchronous machine, an excitation system, a turbine, a governor and a boiler models. The equivalent units are made up of similar models. The parameters of an equivalent model of synchronous machine, excitation system, governor, turbine and boiler are identified for each group of coherent units, by means of a least square fit of their transfer functions. The aggregation technique is demonstrated for a group of three power plant units. The accuracy of the reduced order model is evaluated by comparing time responses of the equivalent model with the response of the full power system model, for 39 buses New England System.