Performance Improvement of a Grid Connected Wind Farm System

IOSR Journal of Electrical and Electronics Engineering (IOSR-JEEE)
e-ISSN: 2278-1676,p-ISSN: 2320-3331, Volume 12, Issue 1 Ver. II (Jan. – Feb. 2017), PP 18-21
www.iosrjournals.org
DOI: 10.9790/1676-1201021821 www.iosrjournals.org 18 | Page
Performance Improvement of a Grid Connected Wind Farm
System
Dr. Gouranga Chandra Biswal
Department of Electrical Engineering Bhilai Institute of Technology, Durg, India
Abstract: Renewable energy sources are becoming more promising means of green energy production. But the
increasingly penetration level of wind energy into existing power system presents many technical challenges.
Power quality is a measure of the system performance. It requires consideration of problems like voltage
regulation, stability, harmonics etc. This paper presents an overview of grid connected system and analysis of
its stability. The system is assumed with fixed speed Induction generator integrated to a weak grid. Change and
improvement in performance is observed with various FACT devices. The simulation model has been developed
in MATLAB/SIMULINK R2016a.
Keywords: Wind Farm Integration, Point of Common Coupling, Reactive Power Compensator, Flexible AC
Transmission system (FACTS)
I. Introduction
With increase in demand of power and decrease of fossil fuels, mankind has been forced to search
alternative sources for the generation of electricity. Wind power in spite of being stochastic in nature has proved
itself as a viable solution to this problem. As the wind turbine technology is developing at a good pace, more
and more wind power plants are being integrated with the conventional form of generation. With the increase in
the ratio of wind generation to conventional generation, several problems related with integration of wind farms
have emerged. These problems are due to distinct properties of the generators used with the conventional form
of generation and wind based generation.
Table 1 below, depicts the world wide data of wind power generation till the end of 2015.
Table 1: Top ten markets by the end of 2015
S. No Country MW %
1 China 1,45,362 34.10
2 USA 75,471 17.50
3 Germany 44,947 10.50
4 India 27,151 06.40
5 Spain 23,025 5.40
6 U.K 13,603 3.20
7 Canada 11,205 2.60
8 France 10,305 2.40
9 Italy 8,958 2.10
10 Brazil 8,715 2.00
Rest of the World 58,275 13.70
World Total 4,32,419 100.00
Source: BTM, Wiser and Bollinger, 2015
In thermal and hydro power based generation, synchronous generators are used while in wind based
generation mostly induction generators are used. Induction and synchronous generators do not exhibit similar
behavior during power system stresses. Moreover, increase in wind power based generation requires a reliable
transmission system for power evacuation to the load centre. As the wind farms are mainly concentrated in far
flung and rural areas their interconnection with the grid becomes a problem. This problem is mainly due to the
existence weak transmission grids in the rural areas.Wind energy system converts the obtainable kinetic energy
in the wind into mechanical energy that can spur an electrical generator. Predominantly, wind power generators
are self excited induction generators. Induction generators characteristics are strongly affected by the massive
reactive power absorbed during their normal operating conditions. This reactive power trouble may engender
dynamic voltage instability in the system. The needed reactive power of induction generator can be provided
either by the grid or self capacitor bank in parallel with the generator stator terminals. The stability of a system
determines whether the system can settle down to the original or close to the steady state after the transients
disappear. Transient stability refers to the capability of a system to maintain synchronous operation in the event
of large disturbances such as multi-phase short-circuit faults or switching of lines. The resulting system response

Performance Improvement of a Grid Connected Wind Farm System
involves large excursions of generator rotor angles and is influenced by the nonlinear power angle relationship.
Stability depends upon both the initial operating conditions of the system and the severity of the disturbance.
Recent development of power electronics introduces the use of flexible ac transmission system (FACTS)
controllers in power systems. FACTS controllers are capable of controlling the network condition in a very fast
manner and this feature of FACTS can be exploited to improve the voltage stability, and steady state and
transient stabilities of a complete power system. Dynamic reactive power compensators are always required to
stabilize the voltage and to supply the desired reactive power at wind generator bus under normal and abnormal
operation. FACTS devices can be very profitable to simultaneously deliver reactive power and support bus
voltage at wind generator interface. The system instability of wind farms based on fixed speed induction
generators is largely caused by the excessive reactive power absorption by the fixed speed induction generators
after fault due to the large rotor slip gained during fault. The STATCOM considerably improve the system
stability during and after disturbances.
FACTS Devices:
Definition of FACTS from records consistent with IEEE, has the abbreviation of flexible AC Transmission
structures, is described as follows:
‘’Alternating current transmission systems incorporating power electronics based and other static controllers
to enhance controllability and power transfer capability‟‟
The solutions to enhance the first-class of deliver of the electrical networks, go through the applications
tendencies in semiconductor power systems, this is to mention, the usage of static power converters in electrical
networks. The technological advances in electricity semiconductors are permitting the improvement of systems
that react greater like a really perfect transfer, completely controllable, admitting high frequencies of
commutation to principal levels of tension and energy. Recent development of energy electronics introduces the
usage of record controllers in power system.It is well known fact that for reactive power compensation FACTs
devices can be used.Table 2. gives an idea about the cost of various reactive power sources including all FACTS
devices. The main disadvantage of FACTS devices is expensive. It provides smooth and fast response to secure
power system during normal and steady state operations. FACTS controllers may be based on thyristors with no
gate turn-off or power devices with gate turn-off capability. FACTS controllers are used for the dynamic control
of voltage, impedance and phase angle of high voltage AC transmission lines.
Table 2. Different FACTS devices as well as their cost
S. No FACTS Device Cost (Rs/kVar)
1 Shunt Capacitor 432
2 Series Capacitor 1080
3 SVC 2160(controlled portions)
4 TCSC 2160(controlled portions)
5 STATCOM 2700
Figure 1. Schematic diagram of a FACT device (SVC)
The thyristor controller and switches provide fast control of the overall SVC reactance between its
capacitive and inductive design limits. Due to the network impedance, this capability translates into dynamic
bus voltage control. As a consequence, the SVC can improve transmission stability and increase power
transmission limits across a given path as shown in figure 1.
Modelling Of Grid Connected Wind Farm:
For modeling and simulation of wind farm as mentioned above MATLAB has been used which is shown in fig.1

Fig 2: SIMULINK model of a grid connected wind farm.
The figure consist of 2 wind farms each of 12MW capacity, and in each farm three different ratings of
wind induction generator is present i.e. 3MW, 4MW and 5MW. The system consists of a 220KV,50-Hz, sub
transmission system with short circuit level of 2500 MVA, feeds a 33 KV distribution system through 220
kV/33kV step down transformer. A 20MVA FACTS device is used as reactive power compensator at the
common point of coupling.
II. Results And Discussions
The dynamic behaviors of the wind farm distribution network with and without the application of an
external three-phase fault with and without reactive power compensation are investigated for „the constant wind
speed‟. The dynamic performance of WTIG for the constant wind speed is analyzed for different cases:
1) Case 1: without Fault and without STATCOM
2) Case 2: without fault and with STATCOM
3) Case 3: with fault and without STATCOM
4) Case 4: with fault and with STATCOM
A consistent wind velocity of 11 m/s is applied to the wind turbine.
The reaction of the lively electricity injected into the network is low in the case1 because no reactive
energy assist in the community, because of insufficient reactive power reimbursement WTIG machine stability
is lost.The active electricity is injected to the distribution network reduces considerably for the cases3 when a 3
phase fault is applied at t=3 sec. and cleared 3.1sec. For the case of machine without STATCOM, the active
strength injected will become very low with and without fault. However, for the cases2&4 of system with
STATCOM, due to the reactive electricity support, the stability of the machine is maintained and the WTIGs
keep delivering the approximate rated electricity to the distribution network after the fault clearance.The
reaction of the WTIG speed will increase, for the case1 and while a three segment fault is carried out at t=3sec.
And cleared 3.1sec.For case3 of device without STATCOM, the system looses balance and the velocity of the
WTIG maintains to growth. For the machine with STATCOM (case2&4), the steadiness of the system is
maintained after the fault clearance. This is due to the fact that, the reactive power supplied through the
STATCOM.The reaction of the WTIG terminal voltage drops drastically for the cases1 and the low voltage
condition starts at t=3sec, at which the fault is implemented and lasts for 3.1sec .For case of system without
STATCOM, the WTIG terminal voltage drops straight away after the fault clearance. For the device with
STATCOM due to reactive energy help, the WTIG terminal voltage is slightly accelerated at once after the fault
clearance. So the system maintains stability and finally the WTIG terminal voltage recovers for both the
cases2&4.The results are shown in fig2 to 5.
Fig. 3: Case1 (without Fault and without STATCOM) Fig. 3 Case2 (without Fault and with STATCOM)

As from figure 2 and 3 it can be inferred that voltage quality as well as stability of the system is
increased by a good margin. Thus, STATCOM turns out to be a good compensator; also the voltage is
maintained at a nominal value. Similarly, the other two cases are also shown in figure 4 and 5.
Fig. 4: Case3 (with Fault and without STATCOM) Fig. 5: Case 4 (with Fault and with STATCOM)
From figure 4 and figure 5 depicting the two cases with faults, the overall system turns out to be stable
as STATCOM helps to regain the nominal voltage back to normal state by providing additional reactive and
active power.
III. Conclusion
This paper investigates the effect of STATCOM in a wind energy connected distribution network. The
stability improvement of a distribution system connected with WTIG is studied. The dynamic behaviors of the
wind farm distribution system with and without the application of an external three-phase fault with and without
STATCOM are investigated. The amount of active power supplied to the grid is more and reactive power
supplied by grid is low for the cases with STATCOM than for the cases without STATCOM. It is also found
that the WTIG with no STATCOM has lower value of rotor speed and has higher value on terminal voltage than
with STATCOM.
References
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Performance Improvement of a Grid Connected Wind Farm System

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Performance Improvement of a Grid Connected Wind Farm System