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the annual energy capture is in the range of 20-30% higher than the fixed speed wind
generator [6] . The use of capacitor banks is eliminated because it has both active and
reactive power control capability which also enhances its contribution to voltage and
load flow distribution control in the power system. The lower mechanical stress
imposed by DFIG on the gearbox extends the life span of this expensive device. The
controllability of the speed makes it possible to use aerodynamic pitch control, which
effectively limits the generated power during high wind speed periods. Flickers
caused by the aerodynamic torque oscillation and the wind gust are greatly reduced
thereby improving the power quality of the network.
Until quite recently, the power system mainly consisted of the synchronous
generators. The behaviour and the characteristic of these conventional generators to
network disturbance are generally well understood by the utility operators. With the
advent of wind power, induction generator technologies are introduced into the power
system. This poses a lot of concern to most utility operators as the response of these
generators to network disturbance is not well understood.
Most existing literature is focused on the analysis of the behavior of power system
networks as a result of wind farm integration [4, 7-9]. In this paper, however, the
behaviour of a wind farm as a result of disturbance in the power system network is the
subject of study. The study is limited to Wind farm (WF) consisting of variable speed
DFIGs.
The rest of the paper is organized as follows; section two presents the model of the
wind conversion system made of variable speed DFIG. In section three, the system
under study is described. Simulation results obtained are discussed in section four
while section five presents the conclusions.
250
1
94.4
200
1
58.7
150
12
0.3
9
3.8
100
7
4.1
59
4
7.6
50
3
9.4
3
1.1
2
3.9
1
0.2
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3.6
1
7.4
7
.
6
6
.1
0
1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010
Year
Fig. 1.
Source: Adapted from [1]
2
Modelling of DFIG Wind Conversion System
Wind conversion system (WCS) comprises of the aerodynamic system, the
mechanical shaft system, electrical system of the induction generator, the pitch
control system, the speed control system, the rotor side converter controller and the
grid side converter controller. All these systems are combined together to form a unit
system of a wind farm as depicted in Fig 2.
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