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

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

• Peter Tavner
• Wind Technologies Ltd

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Brushless DFIG Drivetrain
Generator DFIG
Gearbox x3
AC/AC
Gearbox x2
Generator BDFIG
AC/AC
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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.

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Brushless DFIG Operation

• Operates in a synchronous mode
• Converter controls
• Real power
• Reactive power

BDFIG
Synchronous speed
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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

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20 kW Wind Turbine with BDFIG
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
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Assembled 250 kW Brushless DFIG
Frame size 400
Rated power 250 kW
Speed range 500 rpm 36
Rated torque 3670 Nm
Rated voltage 690 V
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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
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250 kW Brushless DFIG Manufacture
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Brushless DFIG Power Converter
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Brushless DFIG Control Hardware
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Rotor Bluetooth Transmission System
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Test Rig Schematic
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250 kW Brushless DFIG Test Area
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Video of test rig
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Heat-Run Test at 250 kW
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Efficiency versus Load
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Dynamic Performance
Applying full power at 100 kW/s
Measured PW real and reactive powers
Simulated PW real and reactive powers
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Dynamic Performance
Applying full power at 100 kW/s
Measured torque
Simulated torque
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Dynamic Performance
Applying full power at 100 kW/s
Measured PW and CW currents
Simulated PW and CW currents
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Low Voltage Ride Through (LVRT) Tests
Grid fault hardware
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Low Voltage Ride Through (LVRT) Tests
Grid fault hardware
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Low Voltage Ride Through (LVRT) Tests
Measured grid voltage
Measured converter current
Reactive current Real current
PW real and reactive currents
Total generated power
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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