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

2. 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

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

4. Model Structure

5. Wound rotor induction generator
Saturation
Generator Model
Reactive power controller
Active power controller
Rotor Side Converter Controller

6. Turbine Model
tip-speed ratio
pitch angle
Pitch Controller

7. Drive-train Model
Grid Model

8. Case 1: Small disturbance, no protection action
Rfault = 0.05 pu
Avg. wind speed = 7.5 m/s

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

10. Case 2: Protection action during super-synchronous speed
Rfault = 0.01 pu
Avg. wind speed = 11 m/s

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

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

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

14. Case 3: Protection action during sub-synchronous speed
Rfault = 0.01 pu
Avg. wind speed = 9 m/s

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

16. Effect of Saturation in the Model
saturation curve
Effect of Saturation in the Model
stator current
rotor current

17. 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