Design and Testing of a 250 kW Medium-Speed Brushless DFIG

1. Design and Testing of a 250 kW Medium-Speed Brushless DFIG Peter Tavner Wind Technologies Ltd

2. Brushless DFIG Drivetrain Generator DFIG Gearbox x3 AC/AC Generator B’DFIG Gearbox x2 AC/AC

3. Brushless DFIG Benefits The Brushless DFIG proposition is to develop from the highly successful cost-effective DFIG WT drivetrain a brushless version that: • Reduces WT drivetrain OPEX costs by: • Raising generator reliability by eliminating brush-gear and slip-rings; • Raising drivetrain reliability by moving to medium speed from high speed, eliminating at least one gearbox stage; • Reduces WT drivetrain CAPEX costs by: • BDFIG retaining the DFIG benefit of a partially-rated Converter; • Lowering weight by moving to a medium speed drivetrain with a BDFIG and 2-stage gearbox; • BDFIG gains improved Grid Code ride-through performance over the DFIG, delivering lower Converter costs.

4. Brushless DFIG Operation • Operates in a synchronous mode • Converter controls • Real power • Reactive power B’DFIG Synchronous speed

5. Progression in Brushless DFIG sizes • 2003 – 6 kW machine at Durham University • 2002 – 7.5 kW machine at Cambridge University • 2008 – 20 kW machine installed into a 20 kW Wind Turbine • 2011 – 250 kW machine built and successfully tested

6. 20 kW Wind Turbine with B’DFIG 20 kW 12.5 m 11 m Brushless DFIG 2 stage helical Fractional – Grid connected Free yaw Rated power Hub height Rotor diameter Generator Gearbox Converter Yaw West Cambridge Site, Cambridge Installed in March 2009

7. Assembled 250 kW Brushless DFIG

8. Brushless DFIG Design Process Initial specification Speed range, supply voltage, operational constraints Analytical design software Pole numbers, machine dimensions, winding turns Steady state performance, electric and magnetic loading, winding currents Equivalent circuit analysis Wind Technologies’ design tools Coupled circuit analysis Dynamic and LVRT performance Current and flux densities, open and closed loop performance Finite Element analysis Final design

9. 250 kW Brushless DFIG Manufacture

10. Brushless DFIG Power Converter

11. Brushless DFIG Control Hardware

12. Rotor Bluetooth Transmission System January 2005

13. Test Rig Schematic

14. 250 kW Brushless DFIG Test Area

15. Video of test rig

16. Heat-Run Test at 250 kW

17. Efficiency versus Load

18. Dynamic Performance Applying full power at 100 kW/s Simulated PW real and reactive powers Measured PW real and reactive powers

19. Dynamic Performance Applying full power at 100 kW/s Measured torque Simulated torque

20. Dynamic Performance Applying full power at 100 kW/s Simulated PW and CW currents Measured PW and CW currents

21. Low Voltage Ride Through (LVRT) Tests Grid fault hardware

22. Low Voltage Ride Through (LVRT) Tests Grid fault hardware

23. Low Voltage Ride Through (LVRT) Tests Measured grid voltage Measured converter current Reactive current Real current Total generated power PW real and reactive currents

24. Conclusions • Brushless DFIG has been steadily developed • Design is fully understood and scalable • 250 kW Brushless DFIG believed to be the largest in existence • Performance as expected – efficiency high • Excellent LVRT performance demonstrated • The team currently designing Multi-MW systems to be fitted in wind turbines