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Project No:01
Project Name: Stability improvement of IG based wind farm using DFIG.
Objectives: Our objective is to improve the stability of a IG based wind farm using DFIG.
Introduction:
Wind turbines have to compete with many other energy sources. It is therefore important
that they should be cost effective. They need to meet any load requirements and produce
energy at a minimum cost per dollar of investment. Performance characteristics such as
power output versus wind speed or versus rotor angular velocity must be optimized in order
to compete with other energy sources. Yearly energy production and its variation with
annual wind statistics must be well known. The shaft torque must be known so that the
shaft can be built with adequate strength and turbine load is properly sized.
The double fed induction generator allows power output into the stator winding as well as
the rotor winding of an induction machine with a wound rotor winding. Using such
a generator, it is possible to get a good power factor even when the machine speed is quite
different from synchronous speed.
Fig-01: Doubly fed induction generator (DFIG) basic diagram in a wind turbine.
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Existing Model-IG:
Fig-02:Induction Generator (IG) Model.
Existing Model-DFIG:
Fig-03: Doubly Fed Induction Generator
Controlling of DFIG:
Controlling principle:
 Two axis current vector control
 Direct torque control
Rotor Side Converter:
To independently control the active power (rotor speed) and
reactive power at the stator terminal.
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Grid Side Converter:
To control of the grid side converter is to maintain the DC-link
capacitor voltage at a set value.
Real and reactive power control :
 Two axis current vector control
Conventional method, d–axis and q-axis current control.
 Direct torque control (DTC)
Controls the machine torque directly by selecting appropriate voltage vectors using the
stator flux and torque information.
Power flow in DFIG :
 Active power flow in the DFIG during sub-synchronous operation.
 Active power flow in the DFIG during super-synchronous operation.
Advantages of DFIG:
 Allow variable speed operation & Higher overall efficiency.
 Reduced acoustical noise, mechanical stress & Use partially-rated power converter
(approximately 30% of generator power) on the rotor circuit
Disadvantages of DFIG:Main drawbacks of the DFIG-based system are the use of
multiphase slip ring assembly with brushes for access to the rotor windings and a protection
issue in the case of grid faults.
Simulation Models :
IG based
wind farm
50 MVA
(10×5=50 MVA)
Grid
Fig-04: IG based wind farm (50 MVA)
IG based
wind farm
40 MVA
(8×5=40 MVA)
Grid
DFIG based
Wind farm
10 MVA
(2×5=10 MVA)
Fig-05: Proposed model (IG & DFIG)
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DFIG Model :
#1
#2
B
B
Va5
B
B
C
C 0.69 [kV]
#2
#1
Ec
Freq/Phase
Measurement
Vb
Vb5
PLL
theta
Vc
Vc5
PG[pu]
QG[pu]
e
25000 [uF]
e
Va
Va
Ia
Ia
PWM
Vb
Vb
Ib
Ib
Inverter
a b c
S
TL
W
W
MOD2
IM
Ic
Ib
Ia
W
c
b
a
TIME
Q
Vw Pmax
Vw Pmax
Inverter
Controller
Va
Va
Vb
Vb
Vc
Vc
Ic
Ic
Vc
Vc
1.0
V
theta W Edc PC
theta W Edc PC
theta1 Edc
theta1 Edc
Ia2
Ia2
Converter
Va2
Va2
Vb2
Ib2
Ib2 Controller Vb2
Ic2
Ic2
0.605 [ohm] 0.01155464887 [H]
C
P P[MW]
Q[pu]
P[pu]
f
Pig
P
+
d
C
Q[MVar] Q
Edc
d
C
0.605 [ohm] 0.01155464887 [H]
f
Vc2
Vc2
A
[H]
0.605 [ohm] 0.01155464887R=0
B
Vc5
Va
Va5
Pig PG[MW]
QG[MVar]
A
B
Vc2
Vc2
Ea
Ea
PLL
theta
+
theta D -
Eb
Eb
Ec
Ec
N
6.0
A
theta1
F
Pi
3 Phase
RMS
converter
0.0 [ohm]
C
C
11 [kV]
A
B
A
P
Power
Q
B
PWM
Vb2
Vb2
0.0 [ohm]
B
B
Vb5
0.0 [ohm]
A
P
Power
Q
B
Va2
Va2
0.0 [ohm]
A
A
5 [MVA]
c
b
a
C
A
NA
Ic2
Ia2
Ib2
Eb
C
C 0.34 [kV]
0.69 [kV]
A
0.0 [ohm]
NB
B
0.0 [ohm]
NC
Ea
ph
A
A
3 [MVA]
Vrms
A
N/D
D
B
C
Tm
Vw
Vw
Pmax
Pmax
Fig-06: PSCAD model of DFIG (5MVA)
Proposed Model:
Fig-07: Proposed PSCAD simulation model (IG & DFIG)
V VG
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Simulation & Results:
Speed (m/s)
16.0
14.0
12.0
10.0
8.0
6.0
100
50
0
150
Time (s)
250
200
300
1.200
1.150
1.100
1.050
1.000
0.950
0.900
0.850
0.800
0
50
100
150
Time (s)
200
250
300
Fig-09: Grid voltage (IG)
60
Real power (MW)
50
40
30
20
10
0
0
50
100
150
Time (s)
200
250
300
Fig-10: Response of real power (IG)
Reactive power
(MVAR)
Voltage (p.u.)
Fig-08: Wind speed
20.0
15.0
10.0
5.0
0.0
-5.0
-10.0
-15.0
-20.0
-25.0
-30.0
0
50
100
150
Time (s)
200
Fig-11: Response of reactive power (IG)
250
300
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50.040
50.020
50.000
49.980
49.960
49.940
0
50
100
150
Time (s)
200
250
300
Fig-12: Grid frequency (IG)
Speed (m/s)
16.0
14.0
12.0
10.0
8.0
6.0
0
100
50
150
Time (s)
250
200
300
Fig-13:Wind Speed
Voltage (p.u.)
Frequency (Hz)
50.040
1.200
1.150
1.100
1.050
1.000
0.950
0.900
0.850
0
50
100
150
Time (s)
200
Fig-14: Grid voltage (Proposed model)
250
300
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60
Real power (MW)
50
40
30
20
10
0
0
50
100
150
Time (s)
200
250
300
Fig-15: Response of real power (proposed model)
Reactive power ( Mvar )
40
30
20
10
0
-10
-20
0
50
100
150
Time (s)
200
250
300
Fig-16: Response of reactive power (proposed model)
Frequency (Hz)
50.040
50.020
50.000
49.980
49.960
49.940
0
50
100
150
Time (s)
200
Fig-17: Grid frequency (proposed model)
250
300
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Vgrid (IG)
1.200
Vgrid (IG & DFIG)
Proposed model
1.150
Voltage (p.u.)
1.100
1.050
1.000
0.950
0.900
0.850
0.800
0
50
100
150
Time (s)
200
250
300
Fig-18: Comparison of grid voltages.
Frequncy of grid (I.G.)
Frequency of grid (IG & DFIG)
Proposed model
Frequency (Hz)
50.020
50.000
49.980
49.960
49.940
0
50
100
150
200
250
300
Time (s)
Fig-19: Comparison of frequencies.
Conclusion: If we use DFIG with IG based wind farm ,then we will find that voltage will
be stable and frequency fluctuation will be less.