Parameterized modal analysis using DIgSILENT Programming Language

Abstract

A parameterized modal analysis is proposed to evaluate power system small signal stability and a simulation procedure using DIgSILENT Programming Language (DPL) is presented for this purpose. Modal analysis, or small-signal stability analysis, refers to the ability of a system to withstand small perturbations around an equilibrium point without reaching instability or displaying sustained oscillations. This is an important problem in real systems as sustained oscillations may cause mechanical failures in generating 2 units and make the system vulnerable to the point of losing stability. In order to define the most critical scenario, the standard approach employed by the industry is to consider the system at its maximum loading. This Chapter proposes that critical scenarios should be further sought as in even lighter loading conditions low frequency oscillations may dangerously appear. Using DPL, the system modal analysis is parameterized in order to search for critical operating points. To validate the importance of employing a parameterized modal analysis, a real case is studied: the Northern Chile Interconnected System. The obtained results applying parameterized modal analysis show that the system in a real operation only requires minor deviations from the programmed operating points to incur in dangerous low frequency oscillations. These results validate the importance of searching for critical scenarios and DPL scripting is used to program the steps of the proposed analysis. The scripts and applications presented in this chapter set the basis for additional development to identify critical scenarios for modal analysis in other real systems. Keywords: Power system dynamics, electromechanical modes, RMS simulations, small signal stability, power system damping.