1. Fault Ride Through Techniques of DFIG-based Wind Energy Systems Presenter: Lingling Fan, Co-authors: Chanxia Zhu, Minqiang Hu (Southeast University, Nanjing China) Assistant Professor Electrical Engineering University of South Florida Tampa, FL 33620 USA 1

2. Outline Objectives Analysis of DFIG behavior during faults Single phase fault ride through Three-phase fault ride through Simulation results Conclusion 2

3. Objective Design control schemes to help DFIG ride through faults Faults: Balanced (symmetrical) or unbalanced (unsymmetrical) In literature, ride through balanced faults and unbalanced faults are treated separately A control scheme for all 3

4. Doubly Fed Induction Generator 4 fmfm RSC AC/DC Pr = sPs Ps GSC DC/AC

5. DFIG converter control loops 5 GSC DC/AC RSC DC/AC

6. Analysis of DFIG behavior during unbalanced faults 6 Unbalanced stator currents Positive sequence (f e ) Negative sequence (-f e ) Zero sequence I r : f e -f m =sf e Rotor currents I r : -f e -f m =-(2-s)f e s: slip = 1-f m /f e f m : electric frequency corresponding to rotating speed. f e : nominal frequency 60 Hz (stator) – 50 Hz (rotating speed) = 10 Hz -60 Hz (stator) – 50 Hz (rotating speed) = -110 Hz

7. 7 Analysis of DFIG behavior during balanced faults

8. Reference frames 8 Pos. Neg. Sequences and DC can be separated by a dc filter!

9. Extraction scheme 9

10. Fault ride through schemes- modify RSC current control loops 10

11. An alternative- PR controller 11

12. Simulation Results – unbalanced fault 12

13. Simulation Results – unbalanced fault 13

14. Simulation Results – unbalanced fault 14

15. Simulation results – balanced fault 15

16. Simulation results – balanced fault 16

17. Conclusion Proportional Resonant control is proposed for RSC to mitigate rotor current high frequency components and surge. Simulation results demonstrate the effectiveness. A major contribution: both unbalanced and balanced faults are considered. 17