Sci.Int.(Lahore),25(4),703-706,2013
ISSN 1013-5316; CODEN: SINTE 8
703
COMPARISON OF USING SVC AND STATCOM TO PROVIDE
REACTIVE POWER FOR A GRID-CONNECTED WIND POWER
PLANT TO STABILIZE THE OUTPUT VOLTAGE DURING
STARTUP AND FAULT CONDITIONS
Faegheh Irannezhad1, Behrooz Vahidi1*, Mehrdad Abedi1, Mohammad Rashidi1
1
-Department of Electrical Engineering, Amirkabir University of Technology
Tehran 1591634311, Iran
* Corresponding author email: vahidi@aut.ac.ir
ABSTRACT: In this paper our study highlights the stability of wind farms with Fixed Speed Induction
Generators (FSIG) during startup and fault conditions. Also, focusing at the use of Static Var Compensator
(SVC) and Static Synchronous Compensator (STATCOM) to improve the performance of wind farms to
investigate. Due to the nature of an Asynchronous Generator during starting and fault condition and
because of the large amount of slip of rotor, generator consumes a large amount of reactive power that it
causes variation in small networks and changing in voltage level profile. Here in this exercise we illustrate
the necessity of using compensators using previous works and then by using of wind turbine model in
MATLAB we applied it in our network and simulated this network with SVC and STATCOM, and finally we
discuss output diagrams.
Key Words: Power Quality, SVC, STATCOM, Wind Power Plant
1. INTRODUCTION
With the progress of industrial society and the increasing
needs for energy and especially electrical energies and
increasing environmental and economical concerns and
Concerns about the ending of fossil energy resources in the
world using of wind energy to generate electricity has been
widely considered word-wide and wind generator in large
scale has been installed. For optimal utilization and
expecting outputs of such generators one of the fundamental
topic is the system simulation and modeling error conditions.
Voltage control has always been one of the most important
power quality parameters. The wind power generators, while
using the induction capacity and sensitivity of this kind of
generators, encounter significant reduction in voltage
profiles most of the time. Thus we should control the voltage
fluctuation precipitately. So we can use the reactive power
compensators like capacitor bank, SVC and STATCOM to
regulate and control output voltage of wind generator [1].
As for the importance and widespread usage of reactive
power compensator in voltage regulation in power systems,
we target just to discuss the voltage regulation of this
equipment and not the harmonic reduction or increase in the
transmission capacity of this equipment in this paper.
2. NECESSITY OF USING OF REACTIVE POWER
COMPENSATOR IN WIND POWER PLANTS
We usually use induction generator in wind turbines.
Induction generators because of consumption of reactive
power cause reduction in voltage profile of wind power
plants. Erstwhile they connect the wind turbine straight to
grid to compensate the requirement of reactive power from
grid. But increasing the number of wind power plants causes
other problems. Therefore, manufacturers are looking for
better solutions to supply reactive power. Induction
generator during start-up requires current of about 7 to 8
times larger than its nominal range at 1.5 second and it
causes sudden reducing in the operating voltage of power
plant [2].
Reactive power compensation of wind instruments is
classified into three categories:
1. Static Var Compensator SVC
2. Static synchronous Compensator STATCOM
3. Switchable Capacitor Banks
2.1. Static Var Compensator SVC [1]
One of the methods of Reactive power compensation for
wind power plants is the utilization of SVC. SVCs are
reactive power generator or a kind of var static absorber that
is connected in parallel to grid and its output regulate to
swapping the capacitor or inductor current. In this way we
can maintain and control the voltage in the licensed range.
Static Var Compensator containing three categorize:
1. Thyristor Controlled Reactor TCR
2. Thyristor Switched Capacitors TSC
3. Fixed and reactive capacitor controlled by thyristor
TCR/FC
4. Thyristor-controlled
compensator
and
thyristorcontrolled reactor bank TSC/TCR
Usually in wind power plants we use the Thyristorcontrolled compensator and thyristor-controlled reactor bank
TSC/TCR [3].
This compensators act like a dynamic reactive power control
device. SVCs have a maximum and minimum capacity that
can control reactive power in this range and finally it causes
the voltage stability in wind power plants. SVCs will be
designed and constructed so that in its performance range
response continuous and smooth to sudden changes in
voltage and prevent voltage collapse. These compensators
usually install in a local network bus of wind power plant
and they increase the reliability. SVC control system block
diagram is shown in figure 1.
Using the SVC voltage profile greatly improved than the
non-compensated and compensated capacitor and
detrimental effect of step changes in capacitor banks on
mechanical equipment occurs slowly and softly with SVCs.
704
ISSN 1013-5316; CODEN: SINTE 8
Sci.Int.(Lahore),25(4),703-706,2013
its maximum rated value in the condition of maximum
induction output current (IQmax = ICmax), Icmax is maximum
capacitor current of compensation and ILmax is maximum
SUBSTATION
WT1
20kV
WT2
Figure 1. The block diagram of control system of SVC
2.2. Static Synchronous Compensator (STATCOM):
Another compensator that can be used in wind power plants
is STATCOM. The operation of this compensation
instrument is based on voltage source converter (VSC) or
current source converter (CSC). In this compensators power
electronic semiconductors IGCT, IBT and GTO are used.
Here output AC voltage of VSCs controlled automatically
and in amount that necessary adjust inductive current
required by inductor generators in local network bus. Also
this compensator can act as a harmonic active filter [4].
This compensators cause voltage regulation in output
voltage of wind turbines and improve voltage stability in
transient faults. And like SVCs have faster response and
slowly and softness effect on transient errors than the noncompensated and compensated capacitor and by apply a kind
of dynamic voltage profile control can maintain the voltage
sufficient [5].
3. DESIGN TO REGULATE VOLTAGE SLOPE
In order to meet the general requirements for designing of
compensators in wind power plants, output reactive power of
compensator should be controlled to maintain and change
the voltage at the junction with the power system. Figure 2
shows the location of compensator in the power network.
The voltage of output terminal of Induction generators in
wind turbine allowed varying within defined standards.
Here ∆Vcmax is Deviation (decrease) of terminal voltage in
maximum rated value of the capacitor current (IQmax = ICmax),
and ∆VLmax is deviation (increase) of terminal voltage from
WT3
690/20
Kv
Reactive
Power
Compensation
Figure 2. A view of local network of wind power plant
VRe f
VRe f
KIQ
(1)
In this equation K is adjustment slope and defines like Eq.
(2):
K
Vc m ax
I c m ax
V L m ax
I L m ax
(2)
induction current of compensation [5] and [6].
Eq. (1) shows that Vref, by increasing in compensation
current (That is determined by selective slope K) is
controlled to be less than the nominal voltage
(uncompensated). And conversely is controlled to increase
with the increase in nominal compensation current. Order to
maximum capacitor current or maximum induction current is
achieved [7].
From desirable characteristics of terminal voltage versus
output current of compensator With a control loop, a signal
can being produced commensurate with the extent of KIQ
and with the determined polarity and add to reference
voltage. Effective reference of Vref that control terminal
voltage is like Eq. (1):
Figure 3. Our case study Using MATLAB library
ISSN 1013-5316; CODEN: SINTE 8
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6. CONCLUSION
Because of the increasing use of wind power it seems that it
is necessary to discuss important problems of wind power
plants like their voltage profile. In case of induction
generator the best way to solve this problem of voltage drop
is using of reactive power compensator. According to studies
using of SVC or STATCOM is beneficial way than capacitor
banks. This is because that changes is not step and sudden
and its response occurs soft and slow. Also the time of
response to transient error will reduce and voltage stability
will be improved considerably.
And finally all these factors will increase the reliability of
wind power plants. So it seems inevitable to use SVC or
STATCOM in wind power plants.
Our studies show that STATCOMs have faster response in
compensation and correction of voltage profile than SVC.
Also The SVC has better performance in the long term and
except transient conditions. But since our purpose is mainly
to prevent system instability in certain circumstances and is
mainly transient conditions, so with regardless of the cost
and higher casualties of STATCOMs we can prefer
STATCOM over SVC.
1.3
1.2
1.1
1
Vabc-without(pu)
4. CASE STUDY
In generation part, our generator based on MATLAB library
is composed of a 9MW wind power farm. This farm is
composed of 6 unit of 1.5MW turbine that is connected to
25kV distribution grid, which transfers energy to the 120kV
grid. 25 kV feeders are 30 km long. In generation part we
have 2300V and 2MVA series consist of a motor load
(1.68MW induction motor load with PF0.93) and a 200MW
resistive load that is connected to the same feeder at bus
25kV. A 500kW load is located on 575 V bus of wind farm.
Figure 3 shows our grid.
5. OUTPUT
5.1. Voltage of 25 kV Feeders
In this chart, the output voltage of 25 kV feeders and the
difference between the compensated and uncompensated
network have been shown.
Figure 4-1 shows the output voltage of a compensated
network, Figure 4-2 the shows output voltage of a network
that compensate with STATCOM and figure 4-3 shows the
output of a network with SVC compensation.
5.2. Comparison between the Reactive Power
Compensators at Wind Power Plants
As was mentioned using of power grid to supply required
reactive power for wind power plants is not suitable method
and may create a serious problems. Another method is using
of capacitor banks that nowadays is most common in power
plants. Cheap and low cost of these capacitors is one of the
practical advantages of this method. And improve voltage
profile and correction of power factor of induction generator.
But that creates problems, including step and sudden
changes in capacitors and the stress and sudden changes in
wind turbine gearboxes that causes depreciation and loss of
life of wind turbine and finally their response to transient
errors are very slow [8]. Using of SVC and STATCOM
versus previous method we will see a significant
improvement. Quick and appropriately response to sudden
and transient changes in the system, improve voltage
stability and voltage profile are some of the main advantages
of this methods. Increasing the reliability of wind power
plants in large and small disturbances is another benefit of
compensators [3].
The ability to provide the maximum offset voltage of the
reduced system compensation with SVC and STATCOM
has better response and the ability of STATCOM to keep
output capacitor current in low voltage of system make
STATCOM more fruitful than SVC to improve transient
stability [5] and [6].
As shown in figure 4-2, figure 4-3 STATCOM does
compensation and correction of voltage profile faster than
SVC. But SVC has a better performance in long the long
term. But since our purpose is mainly to prevent system
instability in certain circumstances and mainly transient fault
thus regardless of higher cost and losses of STATCOM over
SVC, we might prefer STATCOM to SVC.
Comparison between compensator is given in table I.
0.9
0.8
0.7
0.6
0.5
0.4
0
2
4
6
8
10
Time(sec)
12
14
16
18
20
Figure 4-1: 25kV bus voltage without compensator
1.3
Va
Vb
Vc
1.2
1.1
Vabc-bus-statcom(pu)
Sci.Int.(Lahore),25(4),703-706,2013
1
0.9
0.8
0.7
0.6
0.5
0
2
4
6
8
10
Time(sec)
12
14
16
Figure 4-2: 25kV bus voltage using STATCOM.
18
20
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1.6
1.4
Vabc-bus-svc(pu)
1.2
1
0.8
0.6
0.4
0.2
0
2
4
6
8
10
Time(sec)
12
14
16
18
Figure 4-3; 25kV bus voltage using SVC
Table I: Comparison Between Compensator
SVC
compensator
Type
Losses
Harmonic
Maximum
delay
Transient
behavior of
system during
voltage
turbulence
Maintenance
cost
Compensation
cost
TCRTCR-FC
TSC
Controlled
Impedance
Low
Low
1 cycle
High
0.5 cycle
STATCO
M
Synchrono
us voltage
source
Medium
Very low
withdraw
Medium
Good
Medium
Medium
Medium
High
20
Sci.Int.(Lahore),25(4),703-706,2013
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STATCOM”, 22th ICEE, (in Persian), 2007.
[5] Abdel – Rahman, M. H. Youssef, F. M. H. and Saber, A.
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