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Ride-Through of DFIG Operation at
Dead-band around Synchronous Speed
Prof. Kashem Muttaqi, and Mr. Yingjie Tan
School of Electrical, Computer and
Telecommunications Engineering,
University of Wollongong, NSW 2522 Australia
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Introduction
Doubly-Fed Induction Generator (DFIG)
Torque sensor
Gearbox
G
G
Grid
Tm
RSC
GSC
Turbine
Crowbar
Encoder
ira,b,c
ωr
ωr
Tm
Crowbar Cgate
Controller
Torque Tref
Controller
[iRd]ref
P0
Power
calculation
vsa,b,c
iga,b,c
isa,b,c
PWM
ira,b,c [vra,b,c]ref
θr,ωr
RSC
controller
VDC
[igq]ref
θs φsd ωs
Stator flux
estimator isa,b,c
PWM
[vga,b,c]ref
iga,b,c
GSC
controller
ωe
θe
PLL
vsa,b,c
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Low Rotor Current Frequency around
Synchronous Speed
Frequency of rotor current
𝝎𝒓 = 𝒔 𝝎𝒔
ω𝑠 −Frequency of stator current.
𝑠 −Frequency of stator current.
𝝎𝒔 − 𝝎𝒎
𝒔=
𝝎𝒔
ω𝑚 −Angular frequency of rotor speed.
The closer to the
synchronous speed, the
lower the frequency of rotor
currents.
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Problems
1. unbalanced heating
At synchronous speed,
the power losses spread
unequally among the half
bridges.
Source: M. Bruns, B. Rabelo, and W. Hofmann, "Investigation of doubly-fed induction generator
drives behaviour at synchronous operating point in wind turbines," in Proc. Power Electronics and
Applications, 2009. EPE '09. 13th European Conference on, 2009, pp. 1-10.
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Problems(Cont.)
2. Excessive maximum junction temperature
The maximum
temperature of IGBT is
higher at lower
frequencies of rotor
voltage.
Source: M. Z. Sujod, I. Erlich, and S. Engelhardt, "Improving the reactive power capability of the
dfig-based wind turbine during operation around the synchronous speed," IEEE Trans. Energy
Convers., vol. 28, no. 3, pp. 736-745, 2013.
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Problems(Cont.)
3. High junction temperature swings
The lower the frequency
of rotor current, the
higher the deviation in
junction temperature
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Solutions
1. Switching frequency reduction method
ΔT is larger than T,
frequency reduction is
implemented.
Source: L. Wei, J. McGuire, and R. A. Lukaszewski, "Analysis of PWM frequency control to improve
the lifetime of PWM inverter," IEEE Trans. Ind. Appl., vol. 47, no. 2, pp. 922-929, 2011.
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Solutions (Cont.)
2. Advanced pulse-width-modulation methods
Selecting appropriate
PWM type is necessary
in a different rotor speed
operating mode to have
lowest IGBT/diode power
losses and increases the
permissible output
current of RSC.
Source: M. Z. Sujod, I. Erlich, and S. Engelhardt, "Improving the reactive power capability of the
dfig-based wind turbine during operation around the synchronous speed," IEEE Trans. Energy
Convers., vol. 28, no. 3, pp. 736-745, 2013.
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Solutions (Cont.)
3. Proposed suboptimal maximum power point tracking
strategy
MPPT
SOPPT
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Solutions (Cont.)
3. Proposed multi-mode operation using crowbar
DFIG deadband: [ωs-ε, ωs+ε]
IG mode:
[ωl, ωh ]
13 m/s
1
IG Mode
with rotor
shortcircuited
directly
Torque (p.u.)
12 m/s
DFIG Mode
0.8
11 m/s
10 m/s
0.6
9 m/s
8 m/s
0.4
0.2
0
0.3
R=Rr+Rcb
A
B
7 m/s
6 m/s
5 m/s
0.6
R=Rr
0.9
Rotor Speed (p.u.)
1.2
1.5
IG Mode with
rotor shortcircuited
through
crowbar
resistor
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Solutions (Cont.)
3. Proposed multi-mode operation using crowbar (cont.)
DFIG Mode
IG Mode
DFIG Mode
DFIG Mode
IG Mode
DFIG Mode
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Conclusion
• Due to the low frequency of rotor current around synchronous
speed operating point in a DFIG based wind turbine generation
system, operating DFIG around synchronous speed can cause
thermal heating problem to the rotor windings as well as
semiconductor devices at the rotor side converter, which may
reduce the lifetime of the system.
• Ride through strategies should be implemented to either enable
safe operation around synchronous speed or to avoid operation
around synchronous speed, hence, reducing the maintenance and
operation cost and improving the reliability of the power supply.
• Two solutions from existing research work have been reviewed
and two approaches have also been proposed for the thermal
heating problem around synchronous speed.
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QUESTIONS?