03-08-2012, 05:00 PM
Power System Stabilization by Synchronous Condenser with Fast Excitation Control
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INTRODUCTION
Power systems with long distance power transmission
lines tend to become unstable when the power flow is
heavy [l]. The power system stability is a key issue to determine
the available transmission power capacity (ATC)
in a power system especially in a deregulated market. Several
kinds of strategies to stabilize the power system have
been proposed and practically implemented so far. Excitation
controls of generator have achieved great success
as a power system stabilizer (PSS) [2]. Recently, semiconductor
controlled power apparatus referred to as flexible
AC transmission systems (FACTS) [3], [4] are also expected
as a powerful countermeasure against every possible
instability in power systems. However, the cost of
power electronics devices does not necessarily meet the
requirement of power systems, which may be an obstacle
to implement the FACTS in power systems.
APPLICATIONOF H-INFINITYCO NTROL SCHEME
TO EXCITATIOCNO NTROL
The control scheme designed according to the classical
method often includes a problem that the control should
be readjusted when the system condition is changed. Otherwise
the control scheme may no longer effectively operate
to satisfy the specification. Here, to avoid this problem
the H-infinity control scheme [8], [9], [lo] has been applied
to the excitation system of synchronous condenser.
The system configuration including the generator, synchronous
condenser, the infinite bus and the transmission
system is relatively simple. However, the system order
is 18th when the detail machine model is used. This is
undesirable in the context of control design especially in
case to apply a sophisticated control design method such
as the H-infinity control. Here, a simplified model for the
control design is derived first.
CONCLUSIONS
In this paper a power system stabilizing control by the
active power control of synchronous condenser using the
rotor revolving energy through the excitation control, is
proposed. Transient stability is improved by the inertia
effect of synchronous condenser just by installing it near
the generator. A control scheme to enhance the damping
of generator oscillation has been derived from the two machine
interconnected system model. Implemented control
scheme is similar to the conventional fast AVR and PSS as
a result. Some simulation results have demonstrated the
significant damping effect on the oscillation of generator
in a long distance bulk power transmission system. Moreover,
the H-infinity control scheme has been applied to the
excitation system of synchronous condenser. In the design
stage, a reduced model consisting of swing equations and
a simplified excitation system for the synchronous condenser,
is derived, where the model parameters have been
adjusted to obtain the frequency characteristics coinciding
with that of original system. As a result, a lower order
H-infinity controller has been designed. Several numerical
examples have demonstrated the significant effectiveness
on stabilization of generator oscillation and the robustness
of controller.