Coherency and aggregation techniques incorporating rotor and voltage dynamics

Dynamic equivalents have been widely used to reduce computational efforts when a large number of scenarios have to be studied to evaluate the stability of interconnected power systems. Most coherency methods developed for model reduction do not consider the effect of voltage variations on the coherency of generators due to weak coupling between real power and voltage. In reality, however, the coherency of generators can be influenced by voltage related factors such as location and speed of AVR controls, generator terminal voltage variation, and load bus voltage variation. The reduced dynamic equivalent is not accurate if the voltage characteristics of the original system are not included in the model. This paper presents coherency identification techniques incorporating rotor and voltage dynamics in order to improve the accuracy of dynamic equivalents. This paper also presents a new method to match the power flow conditions for generator aggregation. This new technique is shown to be critical for the accuracy of aggregated dynamic models. Numerical results based on the model of an actual power system in Asia are presented to demonstrate the performance of the proposed method.