Effect of load increase and power system stabilizer on stability delay margin of a generator excitation control system

Abstract

This paper studies the impact of load increase and a power system stabilizer (PSS) on the stability delay margin of a single-machine-infinite-bus system including an automatic voltage regulator. An analytical method is proposed to determine the stability delay margin of the excitation control system. The proposed method first eliminates transcendental terms in the characteristic equation of the excitation system without making any approximation and transforms the transcendental characteristic equation into a regular polynomial. The key result of the elimination process is that the real roots of the new polynomial correspond to the imaginary roots of the transcendental characteristic equation. With the help of the new polynomial, it is also possible to determine the delay dependency of system stability and the root tendency with respect to the time delay. Delay margins are computed for various loading conditions and PSS gains. It is observed that the delay margin generally decreases as the PSS gain and load demand increase, resulting in a less stable system.

An Accurate Method for Delay Margin Computation for Power System Stability

“…A single machine infinite bus system with AVR and PSS is shown in Figure 2 and the block diagram of the system is shown in Figure 3 [25,30,31]. The time delay is present in the terminal voltage measurement.…”

“…For the stability analysis, the linear model is usually used. The flux-decay model with an exciter is shown in Figure 4 [25,30,31]. PSSs are used in power systems to dampen the inherent oscillations and improve the stability.…”

“…The PSS signal is fed to the AVR to regulate the terminal voltage of the generator. The basic block diagram of a PSS is shown in Figure 5 [25,30,31]. The generator speed deviation is the input signal of the PSS.…”

“…The parameters in the model are defined as [25,30,31]: The SMIB with an exciter: The exciter output voltage, and E fd0 is the reference…”

“…This, in turn, increases the efficiency and reduces the computations. In Reference [25], Rekasius substitution is used to transform the transcendental characteristic equation into normal polynomial and a single-machine-infinite-bus system equipped with an automatic voltage regulator (AVR) and a power system stabilizer (PSS) is chosen as a case study. The delay margin is calculated for different values of the PSS gain.…”