Prony analysis and modeling of a TCSC under modulation control

This paper illustrates the use of Prony signal analysis tools to derive a system model of the thyristor controlled series capacitor (TCSC) located at the Bonneville Power Administration´s (BPA´s) Slatt 500 KV substation near Arlington Oregon. The Slatt TCSC is part of EPRI´s flexible AC transmission systems (FACTS) initiative. The analysis presented in this paper was carried out to find linear models for the TCSC system using Prony analysis and to determine the range of validity for these linear models. Prony analysis is performed on output data files generated by simulations using BPA´s transient stability program (TSP) on the TCSC and surrounding system under both closed and open loop TCSC operation. TSP simulations of the power system are performed using a 2623 bus 455 machine stability model of the western power grid. Root loci of the open loop and closed loop identified systems were generated and the motion of the system´s transfer function poles was compared to those obtained by analyzing the system responses for various TCSC modulation controller gains. Comparisons are also made to the system (via TSP simulations) and transfer function responses in the time domain for both the open and closed loop identified transfer functions. The results shown here illustrate the advantages of closed loop identification and the nonlinearity of the system