Voltage Regulation of Grid Connected Wind Farm
Using STATCOM
Mohammad Ali Tofigh, IEEE Member
Nasrudin Abd Rahim, IEEE Senior Member
Department of Electrical Engineering
University of Malaya
Kuala Lumpur, Malaysia
alitofigh@ieee.org
Department of Electrical Engineering
University of Malaya
Kuala Lumpur, Malaysia
nasrudin@um.edu.my
R. Vigna Kumaran
Department of Electrical Engineering
University Tenaga Nasional
Serdang, Malaysia
vigna@uniten.edu.my
Abstract – This paper presents analysis of voltage regulation by
using STATCOM to reduce voltage fluctuation in the grid
connected wind farms. A STATCOM is installed at the main bus
of power system network, point of common coupling, (PCC),
which wind turbine generator systems (WTGS) or wind
farm is connected to the power system. STATCOM
technology is shown to mitigate voltage fluctuation and to
improve power quality in the power system. This research
concludes with the discussion of voltage regulation analysis and
wind farm problem in power system network. In this research,
PSCAD/EMTDC software is used to model and simulate the
network.
Keywords: STATCOM, point of common coupling (PCC),
voltage fluctuation, wind farm
W
I.
INTRODUCTION
ind energy is one of the green energy resources in
the world. It has grown rapidly as an important
electricity source. Wind turbine is being used as a
generator for producing electricity to the distribution network.
When the rated power of wind turbines is still relatively
small, makes it necessary to group of wind turbines called
wind farms. The power produced by the wind farm is the sum
of the power produced by each wind turbine generator systems
(WTGS). When the wind farm becomes synchronize, for
instance the blade on different wind turbines all turn the
towers at the same time, then the power fluctuation at the
blade passing frequency will add together. The network
voltage fluctuations can be very high [1]. Voltage flicker is
concerned when the connection of large fluctuating loads [2].
Voltage flicker caused by the aerodynamic aspects of a wind
turbine in a wind power system. “The variations in wind speed
and wind direction result in variation and oscillation on the
system voltage, which can be mitigated by a STATCOM” [3].
The capacitor bank capacity of wind generator is reduced by
15% when STATCOM is installed at wind farm. As wind
speed is always fluctuating, the terminal voltage of wind
generator also fluctuates randomly, which has an adverse
effect on the rest of power system. The STATCOM with
reduced capacitor bank can decrease the voltage fluctuations
of multi-machine power system as well as wind generator
terminals [4]. STATCOM technology to have the capability to
increase stability and improve system dynamic response
following disturbances [5].
The application of STATCOMs is to increase power quality
and to reduce transmission line losses which have been also
studied for wind power systems. Generally, STATCOM is to
be installed at the point of common coupling (PCC), where the
wind farm is integrated with the utility system.
In this paper, an asynchronous generator with squirrel-cage
rotors is used as wind turbine generator because of its
advantages such as easy to construct and low operating costs
etc. STATCOM technology is applied to mitigate voltage fluctuation
and to improve power quality in the power system.
II.
POWER SYSTEM MODEL
The rapid increase in the number of wind turbines in power
systems on the one hand and the problems that are caused by
wind turbine on the other hand shows the importance of their
operating in power system analysis. Majority of horizontal
axis wind turbines have two or three blades. In this study, all
of wind turbines are based on 11 kv. There are two different
types of wind turbine generator systems, one of them is
synchronous generator and the other one is synchronous
generator. Figure 1 shows a simple power system.
978-1-4244-4813-5/10/$25.00 ©2010 IEEE
(a) Better performance under low voltage conditions;
(b) Faster response that is independent of the system
conditions and ;
(c) Reduce space requirement (smaller footprint).
Better performance under low voltage conditions;
(1) Faster response that is independent of the system
conditions and ;
(2) Reduce space requirement (smaller footprint).
(3) A STATCOM can be built up which will reduce the
engineering costs.
Figure 1. A simple power system network
In figure 1, (50 km) transmission line with 3 conductors has
been modeled by resistance and inductance, which is
connected to Y-∆ transformers. A fixed load is connected to
the bus. The wind farm (3 wind turbines) are connected to
In a STATCOM with an energy source on the DC side, it is
advisable to control both the magnitude and phase angle of the
injected voltage by the VSC in order to control the power and
reactive power output. A shunt compensator enables to
mitigate voltage fluctuations at the point of common coupling
(PCC).
There are some benefits for shunt compensator
(DSTATCOM), such as [7]:
(1) Limitation voltage swells caused by capacitor
switching.
(2) Reduction of voltage sags due to common feeder
faults.
(3) Controlling the voltage fluctuations caused by
customer load variations, it was found that voltage
fluctuation was reducing from 2.5% to 0.2% with
DSTATCOM.
The voltage regulator has a response time of few cycles
due to STATCOM.
Figure 2. A single phase STATCOM
point of common coupling (PCC) bus. Every wind turbine is
11 kv, 2.0 MVA. Figure 2 shows a single phase STATCOM.
In figure 3, the circuit consists of six switches that made up of
six GTO thyristors connected as a six-pulse voltage source
converters (VSC).
III.
SIMULATION AND RESULTS
In this section, PSCAD/EMTDC is used for wind farm
simulation. As it has been shown in figure 1, wind farm is
connected to point of common coupling (PCC). Wind farm
will be switched at 1.5 seconds. to the bus. Before wind farm
connected to grid should be synchronized at 11 kv. Figure 4 is
shown voltage waveform at point of common coupling (PCC)
before wind farm connected to grid.
Figure 4. Voltage waveform at PCC – before wind farm connection
Figure 3. A six-pulse VSC circuit
A STATCOM has several technical advantages over other
FACTS devices. These advantages are:
The current waveforms before wind farm switched in systems
are shown in figure 5.
As it has been mentioned, STATCOM has been applied to
mitigate of voltage fluctuation and to reduce harmonics.
(a)
(b)
Figure 5. Current waveforms before wind farm connected to grid;
(a) System 1, (b) System 2.
When the wind farm is switched to system, at 1.5seconds, the
voltage of bus point of common coupling (PCC) will be
produced fluctuation. Voltage fluctuation and harmonics are
shown in figure 6.
Figure 6. Voltage fluctuation waveform at 1.5 (s)
Figure 8. Model of STATCOM
Figure 8 has shown model of STATCOM consists of six
switches that made up of six GTO thyristors with anti parallel
diode connected as a six-pulse bridge. The analysis of the
circuit assumes that each switch is turned on only once in a
cycle of supply voltage and conducts for 1800 each. The
controller of STATCOM Is feedback controller working in
stationary ( ) or synchronously rotating (reference frame)
coordinates. The feedback gain matrix is usually based on the
pole assignment technique to guarantee sufficient damping.
Transformer in STATCOM has specification of below:
“3 phase Y-Y, 11kv/6.6 kv , voltage ratio, 2.0 MVA”
Inductances and resistances are used such as filter in the
STATCOM with low value. Value of inductances are
L = 0.1(H) and resistances are R = 100 (ohm).
As it has been shown in figure 6, voltage has been drop up to
9.711 kv. Wind speed has been set to 26 m/s. The current
waveforms during voltage fluctuation is shown in figure 7.
(a)
(a)
(b)
(b)
Figure 7. Current waveforms at 1.5 (s); (a) System 1, (b) System 2
Figure 9. Mitigation of voltage fluctuation wave form due to STATCOM;
(a) Normal scale, (b) Enlarge scale.
The voltage fluctuation mitigation due to STATCOM
connection has been shown in figure 9. According to the
figure voltage drop is up to 10.744 kv and also harmonics
have been reduced. According to footnote (NEC 210-19 FPN
No. 4) in the National Electrical Code states that a voltage
drop of 5% at the furthest receptacle in a branch wiring circuit
is acceptable for normal efficiency. After STATCOM
connection, current waveforms have better response.
(Figure10)
The results obtained were very satisfying. As a result,
STATCOM is more flexible than SVC and capacitor bank.
STATCOM has good performance and fast responsibility. The
point of common coupling (PCC) voltage results have been
shown that voltage stability at wind farm need STATCOM.
ACKNOWLEDGMENT
Here I would like to take the chance to appreciate Professor Dr.
Nasrudin Abd. Rahim, Department of Electrical Engineering,
University of Malaya and Associate Professor Dr. Vigna
Kumaran, Department of Electrical Engineering, University
Tenaga Nasional. Without their generous support, doing this
research would be impossible.
(a)
REFERENCES
[1]
[2]
(b)
[3]
Figure 10. Current waveforms due to STATCOM connection; (a) System 1,
(b) System 2
[4]
As results, the bus voltage is accepted due to STATCOM
application.
IV.
CONCLUSION
Wind farm problems connected to grid have been investigated,
discussed. Wind farm connected to grid using STATCOM has
been simulated using powerful software PSCAD/EMTDC.
[5]
[6]
[7]
Z. Saad-Saoud, , J. Ekanayake, , N. Jenkins, G.Strbac, and M. Lisboa
“Application of STATCOMs to wind farms”. IEE Proceedings
Generation, Transmission and Distribution , 145, pp.511-516, 1998.
T. Chuong and P. V. Hoa, “Study of Grid Integrated System”
International Symposium on Electrical & Electronics Engineering HCM
City, Vietnam: Power and System Engineering, pp. 189 – 194, 2007.
R. Fadaeinedjad, G. Moschopoulos, and M. Moallem, “Using
STATCOM to Mitigate Voltage Fluctuations Due to Aerodynamic
Aspects of Wind Turbines”. IEEE Conference, pp. 3648-3654, IEEE
Xplore, 2008.
S. Muyeen, M. Ali, R. Takahashi, and T. Murata, “Stabilization of Wind
Farms Connected with Multi Machine Power System by Using
STATCOM”, IEEE PowerTech 2007.
L. Qi, J. Langston and M. Steurer, “Applying a STATCOM for Stability
Improvement to an Existing Wind Farm with Fixed-Speed Induction
Generators”, IEEE, 2008.
Z. Lubosny, “Wind Turbine Operation in Electric Power System”,
Berlin, Germany: Springer, 2003.
K. Padiyar, “FACTS controllers in power transmission and
distribution”, Delhi: New Age International Limited, 2007.