| Power
System Contingencies
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Introduction
Power
system voltage control has a hierarchy structure with three levels: the primary,
secondary, and the tertiary voltage control. Over the past 20 yrs, one of the
most successful measures proposed to improve power system voltage regulation has
been the application of secondary voltage control, initiated by the French electricity
company, EDF, and followed by some other electricity utilities in European countries.
The secondary voltage control
closes the control loop of the references value setting of controllers at the
primary level. The primary objective of secondary voltage control is to achieve
better voltage regulation in power systems. In addition, it brings in the extra
benefit of improvement of power system voltage stability, for this application,
several methods to design secondary voltage controllers have been proposed.
The useful concept of secondary voltage control is explored for a new application-the
elimination of the voltage violations in power system contingencies. For this
particular application, the coordination of various secondary voltage controllers
is proposed to be based on a multi agent request -and- answer type of protocol
to between any two agents. The resulted secondary voltage control can only cover
the location where voltage controllers are installed. This paper presents results
of significant progresses in investigating this new application to eliminate voltage
violations in power system contingencies via secondary voltage control.
A collaboration protocol, expressed graphically as finite state machine, is proposed
for the coordination among multiple FACTS voltage controllers. The coordinated
secondary voltage control is suggested to cover multiple locations to eliminate
voltage violations in the adjacent locations to a voltage controller. A novel
scheme of a learning fuzzy logic control is proposed for the design of the secondary
voltage controller. A key parameter of the learning fuzzy logic controller is
proposed to be trained through off-line simulation with the injection of artificial
loads in the controller's adjacent locations. FACTS
(Flexible AC Transmission Systems) Sudden
changes in the power demands or changes in the system conditions in the power
system are often followed by prolonged electromechanical oscillations leading
to power system instability. AC transmission lines are dominantly reactive networks
characterized by their per mile series inductance and shunt capacitances. Suitably
changing the line impedance and thus the real and reactive power flow through
the transmission line is an effective measure for controlling the power system
oscillations and thereby improving the system stability.
Advances in
high power semiconductors and sophisticated electronic control technologies have
led to the development of FACTS. Through FACTS the effective line impedance can
be controlled within a few milliseconds time. Damping of the power system oscillation
is possible through effective changes in the line impedance by employing FACTS
members (SVC, STATCOM, UPFC etc).
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