The document presents 3 cases simulating the dynamic response of a DFIG wind turbine during grid disturbances. Case 1 shows the response to a small disturbance without protection. Cases 2 and 3 simulate a fault during super-synchronous and sub-synchronous operation, respectively, with protection blocking the converter and short-circuiting the rotor. The conclusions note that DFIG provides better voltage recovery than SCIG during small disturbances but may disconnect for severe faults, and saturation effects are important to include in protection design.

1. Chalmers University of Technology
Dynamic Response of grid
Connected Wind Turbine with
DFIG during Disturbances
Abram Perdana, Ola Carlson Jonas Persson
Dept. of Electric Power Engineering Dept. of Electrical Engineering
Chalmers University of Technology Royal Institute of Technology

2. Chalmers University of Technology
Contents of Presentation
1. Background & objectives
2. Model of WT with DFIG
3. Simulation
a. Fault and no protection action
b. Fault in super-synchronous operation +
protection action
c. Fault in sub-synchronous operation + protection
action
4. Effect of saturation
5. Conclusions

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Objectives
Background
Presentation of DFIG’s
DFIG accounts for 50% of behavior during grid
market share disturbances in different
cases
Tightened grid connection
requirements  immunity of
DFIG to external faults is
becoming an issue
Possibilities and constraints
for designing fault ride
through strategy  safe for
both WT and the grid

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Model Structure
ωg igen
vwind Tm Induction
Drive-train The grid
generator
model u gen model
model
Te
ωt
Turbine ur
model fault
Pitch uinf
Rotor-side signal
controller
converter
β model

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Generator Model Rotor Side Converter Controller
Wound rotor induction generator
u s = rs ⋅ i s +
( )
d ψs
+ jωaψ s
Active power controller
dt
( )
Pref Pref Teref Teref ⋅ Ls
− irqref
ωr u s ⋅ Lm
d ψr
+ j (ωa − ωr ) ⋅ψ r
ωr
u r = rr ⋅ i r +
dt
us
Saturation
1,5
Reactive power controller
1
u sref Qsref irdref
- -
0,5 + +
0 us Qs
0 1 2 3 4
Current (pu)

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Turbine Model
pitch angle tip-speed ratio
Pitch Controller
β* 1
ωt s
β
max=90 max=90 rate limit
min=0 min=0 7 deg/sec
ωt *

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Drive-train Model
dωg
2H g = Tg + K s ⋅θtg + Ds ⋅ (ωt − ωg )
dt
Gearbox
Damping
Generator
Stiffness
Turbine
dωt
2H t = Tt − K s ⋅θtg − Ds ⋅ (ωt − ωg )
dt
Grid Model
0.027+j0.164 pu 0.027+j0.164 pu
Fault
DFIG 100 ms Infinite
Pgen = 2 MW (1 pu) Bus
Rfault
Vinf = 1 0o pu

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Case 1: Small disturbance, no protection action
0.027+j0.164 pu 0.027+j0.164 pu
Fault
DFIG 100 ms Infinite
Pgen = 2 MW (1 pu) Bus
Rfault
Vinf = 1 0o pu
Rfault = 0.05 pu
Avg. wind speed = 7.5 m/s

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Case 1: Small disturbance, no protection action
stator current rotor current
terminal voltage
active & turbine &
reactive power generator speed

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Case 2: Protection action during super-synchronous speed
0.027+j0.164 pu 0.027+j0.164 pu
Fault
DFIG 100 ms Infinite
Pgen = 2 MW (1 pu) Bus
Rfault
Vinf = 1 0o pu
Rfault = 0.01 pu
Avg. wind speed = 11 m/s

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Case 2: Protection action during super-synchronous speed
Sequence: ir
A. Fault occurs rotor
circuit
B. If ir > 1.5 pu:
converter is blocked &
rotor is short-circuited
C. Generator is disconnected
D. Fault is cleared

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Case 2: Protection action during super-synchronous speed
terminal voltage stator current
Insertion of external rotor resistance
active power reactive power

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Case 2: Protection action during super-synchronous speed
no disconnection disconnection + acting of pitch angle
generator & turbine speed generator & turbine speed
pitch angle

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Case 3: Protection action during sub-synchronous speed
0.027+j0.164 pu 0.027+j0.164 pu
Fault
DFIG 100 ms Infinite
Pgen = 2 MW (1 pu) Bus
Rfault
Vinf = 1 0o pu
Rfault = 0.01 pu
Avg. wind speed = 9 m/s

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Case 3: Protection action during sub-synchronous speed
terminal voltage stator current
turbine &
generator speed
active power reactive power

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1,5
saturation
Effect of Saturation 1 curve
in the Model
0,5
0
0 1 2 3 4
Current (pu)
stator current rotor current

17. Chalmers University of Technology
Conclusions
• DFIG provides a better terminal voltage recovery compared
to SCIG during (small) disturbance when no converter
blocking occurs,
• for severe voltage dips DFIG will be disconnected from the
grid (with conventional strategy)
– converter blocking during super-synchronous operation
causes high reactive power consumption,
– converter blocking during sub-synchronous operation causes
high reactive and active power absorption and abrupt change
of rotor speed
• Saturation model predicts higher value of stator & rotor
currents, therefore it is important to include in designing
protection