Representation of multiport rational models in an electromagnetic transients program: Networks with lumped and distributed parameters

The use of equivalents which reproduce the electrical network's behavior over a wide frequency range (Frequency Dependent Network Equivalent) is of fundamental importance to carry out electromagnetic transient studies in large-scale power systems, regarding high precision and acceptable computation time. There are several approaches for building these equivalents, being the most utilized the one based on rational models of transfer functions. Currently, due to its efficiency and robustness, the Vector Fitting has been the most used method to obtain these rational models. Thereby, the problem turns out to be how to include these rational functions of the complex frequency s in an electromagnetic transient program, particularly, in the ATP. Therefore, this paper proposes a method to represent multiport rational models (rational models of MIMO - multi-input multi-output transfer functions) in the ATP. The proposed method takes into account the passive and active behavior of the external system. Its accuracy is verified for a network with lumped and distributed parameters.