Post on 14-May-2017
transcript
Electronically Controlled
Compensations and Network
Controllers
FACTS Devices
Dr. M. EL-Shimy 2014 EPM622_523 PS Control - ASU 1
References
Kundur, P. (1994). Power system stability and control. Tata McGraw-Hill
Education.
Miller, T. J. E., & Concordia, C. (1982). Reactive power control in electric
systems.
Ekanayake, J., Jenkins, N., Liyanage, K., Wu, J., & Yokoyama, A. (2012).
Smart grid: technology and applications. Wiley.
Milano, F. (2010). Power system modelling and scripting. Springer.
Acha, E., Agelidis, V., Anaya, O., & Miller, T. J. E. (2001). Power electronic
control in electrical systems. Newnes.
Mathur, R. M., Varma, R. K., & Varma, R. K. (2002). Thyristor-based FACTS controllers for electrical transmission systems (pp. 147-149).
IEEE.
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Power flow control by FACTS devices and FACTS
connections (Shunt, series, and hybrid)
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SVCs SVCs are static shunt compensators
Ideal SVC
From equivalent circuit point of view an SVC is
constructed of controllable shunt reactor (CSR) and
controllable shunt capacitor (CSC)
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An ideal SVC can fix the AC voltage a specific
desired value given that the reactive power
capability limits of an ideal SVC are infinite and
the response time is zero
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Realistic SVCs do not have infinite capacity and
their response time is limited
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Composite SVC – power system characteristics
System
SVC
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Harmonics
TCRs injects only odd harmonics
For single phase TCR
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Three phase TCRs
Delta connected all triple harmonics are
eliminated by the connection
In Y-connection the harmonics are of the same
orders as the single phase TCR
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The SVC voltage regulator processes the
measured system variables and generates an
output signal that is proportional to the desired
reactive-power compensation. Different control variables and transfer functions of the voltage
regulator are used, depending on the specific SVC application.
The measured control variables are compared with a reference signal,
usually Vref , and an error signal is input to the controller transfer
function.
The output of the controller is a per-unit susceptance signal Bref , which
is generated to reduce the error signal to zero in the steady state.
The susceptance signal is subsequently transmitted to the gate pulse–
generation circuit.
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Implementations of current droop
(slope) in the voltage regulator The SVC current is
explicitly measured and
multiplied by afactor
KSL representing current
droop before feeding as
a signal VSL to the
summing junction.
RR = response rate
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In certain cases, it may be difficult to faithfully
obtain the current signal.
This occurs when the SVC is operating close to its
floating state, that is, zero MVA reactive power.
The current signal then comprises a
predominant harmonic component and a
fundamental resistive component corresponding
to the real losses in SVC.
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To overcome this problem, in certain SVC
controllers the reactive power is computed and
fed back instead of using the SVC current.
The reactive-power signal is calculated by
multiplying the phase currents in SVC by a
fundamental-frequency voltage lagging behind
the actual phase voltage by 90o.
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The other easily
realizable option is the
susceptance-droop
feedback demonstrated
It is implicitly assumed
that the SVC bus voltage
remains close to 1 pu;
thus the SVC current
that is strictly equal to
Bref
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The previous loop can be
simplified to the gain-
time constant form
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SVC Applicatio
ns
Increase in steady-state
power-transfer capacity
Enhancement of
transient stability
Augmentation of power-system
damping SVC mitigation
of subsynchro
nous resonance
(SSR)
Prevention of voltage instability
Improvement of
HVDC link performanc
e
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Increase in steady-state power-transfer
capacity
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Let the transmission line be compensated at its
midpoint by an ideal SVC.
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The STATCOM (or SSC) is a shunt-connected
reactive-power compensation device that is
capable of generating and / or absorbing
reactive power and in which the output can be
varied to control the specific parameters of an
electric power system.
A STATCOM connected to the distribution
circuits is normally called a D-STATCOM.
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It is in general a solid-state switching converter
capable of generating or absorbing
independently controllable real and
reactive power at its output terminals
when it is fed from an energy source or energy-storage device at its input terminals.
REM: SVCs can not generate or absorb active power
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STATCOM applications
Dynamic voltage control in transmission and
distribution systems;
Power-oscillation damping in power transmission
systems;
Transient stability enhancement;
Voltage flicker control; and
Control of not only reactive power but also (if
needed) active power in the connected line, requiring
a dc energy source.
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V-I Characteristics
Unlike the SVC,
the STATCOM can provide
full capacitive-reactive power
atany system voltage - even as
low as 0.15 pu.
It is also capable of yielding
the full output of capacitive
generation almost
independently of the system
voltage (constant-current
output at lower voltages).
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