1. An Active Anti-islanding Scheme using Frequency Shift Acceleration Control for Inverter-based DGs
Seul-Ki KIM
KERI

2. Overview Introduction Islanding Condition
Frequency Shift Acceleration Control
Simulation Results
Experimental Results
Conclusions

3. Introduction Islanding operation Anti-islanding (AI) detection methods
Passive
Active
Proposed AI scheme
Zero NDZ
Easy implementation
Minimal PQ impact

4. Islanding Condition

5. Frequency ↑
Frequency ↓
Voltage ↑
Voltage ↓
ΔP = Pload – PDG
ΔQ = Qload – QDG

6. Frequency Shift Acceleration Control
Key concept
If ΔQ = Qload – Qinv > 0, freq. will increase.
then, decrease Qinv so freq. shift can accelerate.
If ΔQ = Qload – Qinv < 0, freq. will decrease.
then, increase Qinv so freq. shift can accelerate.

7. Power controller of common DGs (3-phase)

8. How to implement FSAC in power controller

9. Power controller with FSAC

10. Acceleration gain Kacc
I*q : q-axis current reference
Kw : weighting gain of i*q
Ka : frequency error amplifying gain

11. Weighting gain Kw
Kw > 5.94%  KW = 0.06

12. Amplifying gain Ka
Lower limit by small signal analysis

13. For system to be unstable

14. Amplifying gain Ka
Upper limit by frequency step analysis

15. To obtain Qinv deviation with less than l k l for lΔωl

16. Simulation Circuit (PSCAD/EMTDC)
Simulation Results
Simulation Circuit (PSCAD/EMTDC)

17. Simulation Conditions
Pinv = Pload = 20kW, Qinv = Qload = 0kVar
Detection Conditions (IEEE P1547)
Voltage : 110% > or < 88%
Frequency : 60.5 Hz > or < 59.3 Hz
Duration : over 10 cycles
R-L-C Load conditions (IEEE 929 & UL 1741)
Quality factor Qf = 2.5  QL & QC = 2.5 x Pinv
Gain (Kw = 0.06, 0.85 < Ka < 7.5 )

18. Without FSAC
With FSAC (Kw = 0.06, Ka = 2)

19. Reactive power generation
Frequency shift
D-axis current
Reactive power generation

20. Frequency
Ka = 1.25
Ka = 2

21. Frequency
60  59.8 [Hz]
Qinv
Ka = 7
Qinv
Ka = 2

22. Frequency
60  59.8 [Hz]
Ka = 20
Qinv
Vrms

23. Harmonic Spectrum
Without FSAC
With FSAC

24. Current THD
Current THD with Anti-Islanding

25. Experimental Results Grid Qf = 3.9 6.3kW - j3.5kVar 0kW - j0kVar

26. Before FSAC implementation
Grid Trip Signal
Inverter Voltage
Current injection into Grid
Inverter Current

27. After FSAC implementation (Ka = 2, Kw = 0.06)
Grid Trip Signal
Inverter Voltage
Current injection into Grid
Inverter Current

28. After FSAC implementation (Ka = 0.2, Kw = 0.06)
Grid Trip Signal
Inverter Voltage
Current injection into Grid
Inverter Current

29. After FSAC implementation (Ka = 0.6, Kw = 0.06)
Grid Trip Signal
Inverter Voltage
Current injection into Grid
Inverter Current

30. Conclusions Proposed FSAC Guided How to implement FSAC
Controller
Gain settings
Verified with Simulation and Experimental results
Benefits of FSAC
Zero NDZ possible
Minimized impact on power quality
Easy implementation