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Steady State and Dynamic Performance of an SVC Device With
Matlab/SimPowerSystems
Conference Paper · April 2008
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Bekri Oum El Fadhel Loubaba
Mohammed-Karim Fellah
Taher Moulay University of Saida
University of Sidi-Bel-Abbes
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‫اﻟﻤﻠﺘﻘﻰ اﻟﺪوﻟﻲ اﻟﺜﺎﻧﻲ ﺣﻮل اﻟﻬﻨﺪﺳﺔ اﻟﻜﻬﺮﺑﺎﺋﻴﺔ‬
International Conference on Electrical and Electronics Engineering 21‐23 April 2008
Steady State and Dynamic Performance of
an SVC Device With
Matlab/SimPowerSystems
O. L. BEKRI *
loubabab@yahoo.fr
M.K. FELLAH **
mkfellah@yahoo.fr
*
Institute of Sciences and Technology.
University Center Dr Moulay Tahar, Saïda, Algeria.
I. Phone. : 048 47 47 07
Fax : 048 47 42 62
**
ICEPS laboratory (Intelligent Control & Electrical Power Systems)
Electrical Engineering Department, Engineering Sciences Faculty
University of Sidi Bel-Abbes, Algeria.
Abstract— The Static Var Compensator (SVC) is
generally used as a voltage controller in power systems.
It can help maintain the voltage magnitude at the bus it
is connected to at a desired value during load
variations. The SVC can both absorb as well as supply
reactive power at the bus it is connected to by control
of the firing angle of the thyristor elements.
In this paper, we present the control limits of the SVC
in the first part, and the dynamic performance of the
SVC
in
the
second
part,
using
Matlab/SimPowerSystems.
Keywords— FACTS, SVC, dynamic performance,
SimPowerSystems
Résumé— Le compensateur statique d’énergie réactive
(Static Var Compensator ou SVC) est généralement
utilisé comme un contrôleur de tension dans les
systèmes d’énergie. Il peut aider à maintenir
l’amplitude de la tension dans le noeud où il est
connecté à une valeur désirée lors des variations de
charge. Le SVC peut à la fois absorber ainsi générer
de la puissance réactive au nœud où il est connecté par
le contrôle de l'angle d’amorçage des thyristors.
Dans cet article, nous allons, en premier lieu, présenté
les limites de contrôle du SVC. En seconde partie, nous
présenterons la performance dynamique du SVC en
utilisant
le
logiciel
de
simulation
Matlab/SimPowerSystems.
I.
INTRODUCTION:
The first device in the group of shunt connected
FACTS devices and in the whole family of the
FACTS was the SVC (Static Var Compensator)
appeared about two (2) decades ago [1]. The SVC is
normally installed to prevent excessive voltage
variations at the selected terminal(s) during major
power lines or generating stations being lost and for
a continuous voltage support during the daily load
cycle, but none to control active power flow.
The IEE defines the SVC as “A shunt connected
static Var generator or absorber whose output is
adjusted to exchange capacitive or inductive current
so as to maintain or control specific parameters of
electrical power system (typically a bus voltage)”.
II.
STATIC VAR COMPENSATOR:
SVC is basically a shunt connected static var
generator/load whose output is adjusted to exchange
capacitive or inductive current so as to maintain or
control specific power system variables; typically,
the controlled variable is the SVC bus voltage [2].
One of the major reasons for installing a SVC is to
improve dynamic voltage control and thus increase
system loadability. The two most popular
configurations of this type of shunt controller are the
fixed capacitor (FC) with a thyristor controlled
reactor (TCR), and the thyristor switched capacitor
(TSC) with TCR. Of these two setups, the second
(TSC-TCR) minimizes standby losses; however,
from a steady-state perspective, we can model the
SVC as a variable reactive power source. Figure 1
shows the schematic diagram of a SVC.
A. The Thyristor Controlled Reactor (TCR) [3]:
The TCR consists of a fixed reactor of inductance L
and a bidirectional thyristor valve. In a practical
valve, many thyristors (typically 10 to 40) are
connected in series to meet the required blocking
voltage levels. Applying simultaneously a gate pulse
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International Conference on Electrical and Electronics Engineering 21‐23 April 2008
to all thyristors of a thyristors valve brings the valve
into conduction. The valve will automatically block
approximately at the zero crossings of the AC
current, in the absence of a firing signal. Thus, the
controlling element is the thyristor valve.
•
V =
I
Bl max
SVC is fully inductive
( B = Bl max )
where:
V : Positive sequence voltage (pu)
Vref : Reference voltage (pu)
I : Reactive current (pu/pbase) (I> 0 indicates an
inductive current)
Xs : Slope or droop reactance (pu/pbase).
Bc max :
Maximum
capacitive
susceptance
(pu/pbase) with all TCSs in service, no TSR or
TCR.
Bl max :
Maximum
inductive
susceptance
(pu/pbase) with all TSRs in service or TCRs at
full conduction, no TSC.
Typical values for the slope X s are in the range of
Fig. 1 : Schematic diagram of an SVC
The current TCR is essentially reactive, lagging the
voltage by nearly 90°. The active component of the
current is very small and the losses of the device are
of the order of 0.5 to 2℅ of the reactive power;
therefore, one of the modeling assumptions is that
the resistance of the inductor may be neglected.
Another assumption that is made here is that the
voltage applied to the TCR is sinusoidal, which for
the SVC, a shunt device, is reasonable as the supply
voltage is the bus voltage.
The firing angle α is defined as the angle in
electrical degrees between the positive going zerocrossing of the voltage across the inductor and the
positive going zero crossing of the current through
it. The thyristors are fixed symmetrically; therefore,
the maximum possible firing angle is 180°. Full
conduction is obtained with a gating angle of 90°.
0.02 to 0.05 p.u. with respect to the SVC base. The
slope is needed to avoid hitting limits for small
variations of the bus voltage. At the voltage limits,
the SVC is transformed into a fixed reactance. A
typical value for the controlled voltage range is 10
%.
a. SVC V-I Characteristic [4]:
The SVC can be operated in two different modes:
•
In voltage regulation mode (the voltage is
regulated within limits, as explained
below). See figure 2.
A.1. Control and limits of the SVC:
The steady state control law for the SVC is the
typical current-voltage characteristic the V-I
characteristic is described by the flowing three
equations:
• V = Vref + Xs I SVC
is
in
regulation
range (- Bc max < B < Bl max )
•
V =
I
Bc max
SVC is fully capacitive
Fig. 2: The SVC V-I characteristic in voltage regulation
mode
•
( B = Bc max )
In var control mode (the SVC susceptance
is kept constant). See figure 3.
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International Conference on Electrical and Electronics Engineering 21‐23 April 2008
Fig. 5: The actual positive_sequence susceptance B1 and
control signal output B of the voltage regulator
Fig. 3: The SVC V-I characteristic in var control mode
Primary Voltages
Voltage
Measurement
+
TCR
B
-
Secondary Voltages
pulses
Voltage
Regulator
Vra
Vref
Synchronizing Unit
(PLL)
Pulse Generator
n_TSC
α
Distribution
Unit
TSC
Control System
Fig. 4: single line diagram of an SVC and its Control System Block diagram
As long as the SVC susceptance B stays within the
maximum and minimum susceptance values
imposed by the total reactive power of capacitor
banks (Bcmax) and reactor banks (Blmax), the voltage
is regulated at the reference voltage Vref. However,
a voltage droop is normally used (usually between
1% and 4% at maximum reactive power output).
Figure 6 shows the SVC reactive power output (pu).
A positive value indicates inductive operation.
b. The SVC dynamic response:
The figure 4 shows a single-line diagram of a static
var compensator and a simplified block diagram of
its control system.
From figure 5 to figure 9:
Initially, the source is generating its nominal
voltage. At t= 0.1s, the voltage is decreased
(0.97pu). At t= 0.4s, the voltage is increased
(1.03pu) and finally, at t= 0.7s, return to nominal
voltage (1pu).
Figure 5 shows the actual positive-sequence
susceptance Bactual and control signal output Bcontrol
of the voltage regulator.
Fig. 6: The SVC reactive power output
Figure 7 shows the actual system positive-sequence
voltage Vactual and output Vm of the SVC
measurement system.
Figure 8 compares the SVC susceptance B (output
of the voltage regulator) for two different short
circuit levels: 3000MVA and 600MVA. If we
decrease the system strength, the average time delay
due to valve firing is not negligible and we instead
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‫اﻟﻤﻠﺘﻘﻰ اﻟﺪوﻟﻲ اﻟﺜﺎﻧﻲ ﺣﻮل اﻟﻬﻨﺪﺳﺔ اﻟﻜﻬﺮﺑﺎﺋﻴﺔ‬
International Conference on Electrical and Electronics Engineering 21‐23 April 2008
observe an oscillatory response and eventually
instability.
Fig. 9.b: The phasor current Ib flowing into the
SVC
Fig. 7: The actual system positive-sequence voltage V-I
and output Vm of the SVC measurement system
Fig. 9.c: The phasor current Ic flowing into the SVC
Fig. 8: The SVC susceptance for two different short-circuit
levels: 3000 MVA and 600 MVA
Figure 9 shows the phasor currents Ia, Ib, and Ic
flowing into the SVC.
From figure 10 to 13, we compare the SVC reactive
power with different value of the firing angle α.
Fig. 10: The reactive power for
α = 0°
Fig. 11: The reactive power for
α = 90°
Fig. 9.a: The phasor current Ia flowing into the
SVC
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International Conference on Electrical and Electronics Engineering 21‐23 April 2008
Ia
Va
Fig. 12: The reactive power for
α = 120°
Fig. 13: The reactive power for
Fig. 14: The voltage and the current of the source
α = 180°
Fig. 15: The SVC reactive power
Vmeas
A.2. Dynamic performance of the SVC on a
transmission system
Vref
From figure 14 to figure 17:
Initially, the source voltage is set at 1.004 pu,
resulting in a 1.0 pu voltage at SVC terminals when
the SVC is out of service (fig. 14). As the reference
voltage Vref is set to 1.0 pu, the SVC is initially
floating (zero current). This operating point is
obtained with TSC1 in service and TCR almost at
full conduction (α = 96 degrees) (fig. 15).
At t=0.1s, voltage is suddenly increased to 1.025 pu
(fig. 14). The SVC reacts by absorbing reactive
power (Q=-95 Mvar) to bring the voltage back to
1.01 pu (fig. 15). The 95% settling time is
approximately 135 ms. At this point, all TSCs are
out of service and the TCR is almost at full
conduction (α = 94 degrees) (figure 17).
At t=0.4 s, the source voltage is suddenly lowered to
0.92 pu (fig. 14). The SVC reacts by generating 256
Mvar of reactive power (fig. 15). Thus increasing
the voltage to 0.974 pu. At this point, the three TSCs
are in service and the TCR absorbs approximately
40% of its nominal reactive power (α =120 degrees)
(figure 17).
Fig. 16: Vmeas and Vref
The TSCs are sequentially switched on and off
(figure 18). Each time a TSC is switched on the TCR
α angle changes from 180 degrees (no conduction)
to 90 degrees (full conduction) (figure 17).
Finally, at t=0.7s, the voltage is increased to 1.0 pu
and the SVC reactive power is reduced to zero
(figure 15).
A.3.
Steady-state voltage and current in TCR AB
The figures 19 and 20 simulate steady-state voltage
and current in TCR AB for α =120 degree. The
figure 19 shows the voltage across the TCR and the
current through it, the current and the voltage are not
sinusoidal anymore.
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International Conference on Electrical and Electronics Engineering 21‐23 April 2008
Fig. 20: Thyristor pulses on the TCR AB
Fig. 17: The phase degree TCR
The major contribution of this study can be
summarized as follows:
1. Description of the SVC behavior.
2. Study of Steady-State and Dynamic
Performance
of
the
SVC
using
Matlab/SimPowerSystems: control and limits
of the SVC and dynamic performance of the
SVC on a transmission system.
REFERENCES
[1] A.Oudalov, «Coordinated control of multiple
Fig. 18: The number of TSCs
Iab TCR Vab TCR
Fig. 19: The TCR voltage and current in branch AB
III.
CONCLUSION
The simulation described in this article illustrates
application of SimPowerSystems to study the
steady-state and dynamic performance of a static var
compensator (SVC) on a transmission system.
The SVC is a shunt device of the Flexible AC
Transmission Systems (FACTS) family using power
electronics. It regulates voltage by generating or
absorbing reactive power.
FACTS devices in an electric power system»,
thesis presented to the Engineering Sciences
Faculty, Lausanne, Switzerland 2003.
[2] N. Mithulananthan, C. A. Cañizares, J. Reeve,
and G. J. Rogers, "Comparison of PSSS, SVC
and STATCOM Controllers for Damping Power
System Oscillations," IEEE Transactions on
Power Systems, Vol. 18, No. 2, May 2003, pp.
786-792.
[3] C.A. Canizares, « Modeling of TCR and VSI
Based FACTS Controllers " Report AT-UCR
99/595, ENEL Ricerca, Area Trasmissione e
Dispacciamento, Milan, Italy, December 1999.
[4] Mathworks/SimPowerSystems, 7.5 version,
2007.
[5] C.A. Canizares, and Z. Faur, «Analysis of SVC
and TCSC controllers in voltage collapse», IEEE
Transactions on Power Systems, Vol. 14, No. 1,
February 1999, pp. 158-165.
Loubaba Bekri : received her Bachelor (1986) and Engineers
(1992) degree in Electrical Engineering from Sidi Bel-Abbes
University in Algeria, and her Master (2002) from ENSET,
Oran,Algeria. She worked in University Center Dr Moulay Tahar,
Saïda, Algeria from 1992 to 2008.
Mohammed Karim Fellah : was born in Oran, Algeria, in 1963.
He received the Eng. degree in Electrical Engineering from
University of Sciences and Technology, Oran, Algeria, in 1986,
and The Ph.D. degree from National Polytechnic Institute of
Lorraine (Nancy, France) in 1991.
Since 1992, he is Professor at the University of Sidi-bel-Abbes
(Algeria) and Director of the Intelligent Control and Electrical
Power Systems Laboratory at this University. His current research
interest includes Power Electronics, HVDC links, and Drives.
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