The Power System Stabilizer (PSS) uses auxiliary stabilizing signals to control the
excitation system so as to improve the power system's dynamic performance. The application
of PSS can help in damping rotor oscillations and improve the stability of the system. If
no adequate damping is available, the oscillation can increase and cause system
separation. PSS is installed in the power generator to help the damping of power system
oscillations. To enhance power stability, various techniques are adopted in the design of Power
System Stabilizer (PSS) like adaptive and self-tuning control in which the output of PSS is
varied with load condition. Low frequency oscillation can be created by small disturbances
in the system, such as changes in the load, and are normally analyzed through the
small signal stability of the power system. These small disturbances head to a steady
increase or decrease in generator rotor angle caused by the lack of synchronizing torque or
to rotor oscillations of increasing amplitude due to a lack of sufficient damping torque.
The most typical instability is the lack of sufficient damping torque on the rotor's low
frequency oscillation. PSS is the most effective device for stabilizing and damping low
frequency oscillation while increasing the stability margin of the power system (Omer, 2006).
A
PSS prepares a supplementary input signal in-phase with the synchronous rotor speed
deviation for excitation systems, resulting in generator stability. Robust controllers are based on
the optimization of the -norm of the transfer matrix between the system disturbance
and its output via linear matrix inequalities (Ahmed et al., 1996; and Silijak et al.,
2004). DeMello and Concordia (1969) introduced a model with a single machine connected
to an infinite bus, which is used to analyze the nature of the low-frequency
electromechanical oscillations in power systems. The PSS has been used by utilities in real power
systems as it has been shown to be the most cost effective electromechanical damping
control (Kundur et al., 1989; and Kundur, 1994). Recently, many modern techniques have
been used to design different PSS structures. However, utilities prefer to choose
lead-lag structure due to its simple structure and reliability in real power systems.
In the past two decades, various types of PSS have been designed. For
example, adaptive controller-based PSS have been used in many applications (Larson and
Swann, 1981). Most of these controllers are based on system identifications and
parameter estimations, therefore from the computational point of view, they are time consuming.
It is evident from the various publications that interest in application of Fuzzy
Logic-based PSS (FLPSS) has also grown in recent years (Nallathambi and Neelakantan, 2004).
Low computation burden, simplicity and robustness make FLPSS suitable for
stabilization purposes. Different methods for designing such devices are proposed using
Genetic Algorithm (GA) and artificial neural network (Cheng et al., 1986; Wenxin et al., 2003; and Michele and Richard, 2005). |
