Multi-port equivalencing of external systems for simulation of switching transients

A multi-port external system equivalent model to simulate switching transients is developed based on direct time domain techniques, as opposed to the currently available models based on frequency domain methods. The model comprises discrete-time filters, which are built using the external system´s response at each of the M ports to a multisine excitation signal and solving a system identification problem. At each port, the filters obtained are converted into an equivalent Norton circuit consisting of M current sources (in parallel). A unique feature of the model is that it explicitly incorporates the travel time delay between the ports. The complete M-port model, having M decoupled equivalent Norton circuits, is easily integrated into the discrete-time representation of the study subsystem. The proposed model is validated by simulating the line energization and post-fault transients in a study subsystem connected at two ports to an external system