Design and Performance Analysis of a 5 MW Medium-Speed Brushless DFIG drive-train

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Design and Performance Analysis of a 5 MW
Medium-Speed Brushless DFIG drive-train

• Peter Tavner
• Wind Technologies Ltd
• Past President of European Academy of Wind Energy

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Overview

• Wind Technologies Brushless DFIG propositions
• History of the Brushless DFIG
• Wind Technologies progress in machine sizes
• Design of a 5 MW brushless DFIG generator
• Comparison of different wind turbine
  drive-trains
• Conclusions.

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Brushless DFIG drive-train
Generator DFIG
Gearbox x3
Partially-rated AC/AC
Gearbox x1 or x2
Generator BDFIG
Partially-rated AC/AC
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Brushless DFIG Operation

• Synchronous mode operation
• Converter controls
• Real power
• Reactive power

Synchronous speed
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Why is Brushless Better?
DFIG Brushless DFIG
Converter Rating Partially-rated Partially-rated
No Brushes/Slip rings r a
Gearbox 3 stage 1 or 2 stage
Grid Compatible Partially Fully
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History of the Brushless DFIG

• 1902- Siemens patent based on Lydall , 2 WRIM
  with connected rotors
• 1907 1914- First Hunt papers, 2 WRIM
  incorporated in a frame with 1 rotor winding
• 1920s- Integration into 1 machine in 1 frame
  realised commercially in Germany UK
• 1930s- Practical cascade-mode BDFM machines
  produced for rock-crushing and ship propulsion
  applications in UK , Germany USA
• 1970- Broadway paper design analysis for the
  integrated machine, nested loop rotor winding
  synchronous mode of operation
• 1980s- Weier proposed and installed a
  cascade-mode BDFM for limited range variable
  speed wind turbine with a small size converter
• 1990s-Introduction of large rating IGBT Voltage
  Source Converters
• 1990s-Some work in Brazil by WEG
• 2000s-Wind Technologies at Cambridge University
  and later Durham University started to develop
  synchronous-mode BDFIG with IGBT VSC,
  specifically to replace DFIG but retain
  partially-rated converter in large wind turbines,
  44 papers published
• 2010-Wind Technologies IP consists of 3 Patents
  50 man-years work covering Electromagnetic design
  of the BDFIG and control of its partially-rated
  Converter

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Wind Technologies Progression in Brushless DFIG
sizes
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20 kW Brushless DFIG Wind Turbine
20 kW 12.5 m 11 m Brushless DFIG 2 stage
helical Grid connected, partially-rated Free
yaw, down-wind
Rated power Hub height Rotor diameter Generator
Gearbox Converter Yaw
West Cambridge Site, Cambridge In operation from
March 2009
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Manufacturing process for 250 kW Brushless DFIG
2 winding stator, 4 pole 8 pole
1 winding rotor, 6 pole
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Assembled 250 kW Brushless DFIG
Frame size 400
Rated power 250 kW
Speed range 500 rev/min 36
Rated torque 3670 Nm
Rated voltage 690 V
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Proposed 5 MW Brushless DFIG Design Specification
Parameter Value Unit
Rotor Diameter 115 m
Hub Height 120 m
Turbine Rotational Speed 7.7 16.5 rev/min
Cut in wind-speed 3.5 m/s
Rated wind-speed 12 m/s
Parameter BDFIG_2G BDFIG_1G BDFIG_1G Unit
Natural Speed 300 88 88 rev/min
Speed Range 192-408 56-120 56-120 rev/min
Gearbox Ratio 27.7 7.25 7.25
Nominal Voltage 690 690 690 V
Grid Frequency 50 50 50 Hz
Rated Power 5 MW 5 MW 5 MW MW
Rated Torque 121 121 416 kNm
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Design Process For Brushless DFIG
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Equivalent Circuit
Parameter BDFIG_2G BDFIG_1G
R1 (mO) 4.2 5.12
R2 (mO) 4.2 5.18
Rr (mO) 6.8 38.14
Lm1 (mH) 18.05 7.68
Lm2 (mH) 12.46 6.89
Lr (mH) 3.14 6.84
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Finite Element Analysis Flux Distribution
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5 MW Brushless DFIG Design
BDFIG_2G BDFIG_1G Units
Supply
Grid Voltage 690 690 V
Grid Frequency 50 50 Hz

Stator
PW Pole Number 4 32
CW Pole Number 12 36
Winding Configuration Delta Delta
PW Full Load Current 1859 1940 A
CW Full Load Current 760 801 A
Airgap Diameter 2191 3800 mm

Common
Rotor Pole Number 8 34
Stack Length 631 761 mm
Electrical Steel Grade 450/65 450/65 W/kg/mm
Speed range 192 - 408 56 120 rev/min
Torque 121 416 kNm
Rated Power 5000 5000 kW
Efficiency 96.6 95.7
Total Active Mass 9.45 12.39 Tonne
Rotor Inertia 11183 122110 kg.m2
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Drive-train Technologies
Architecture Gearbox Generator
High-speed 3-stage PMG/DFIG
Medium-speed 1- or 2-stage PMG/BDFIG
Direct Drive PMG
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Comparison of different wind turbine drive-trains
Gearbox 3G 3G 2G 1G 1G DD
Generator DFIG PMG BDFIG PMG BDFIG PMG
Generator dimensions
Rated speed (rev/min) 1200 1200 410 107 107 14.8
Airgap diameter (m) 0.84 0.84 2.2 3.6 3.8 7.5
Stator length (m) 1.15 0.94 0.63 0.68 0.76 1.25
Number of pole pairs 3 25 8/12 80 16/18 147
Weight
Generator (Tonne) 19.7 3.4 15.4 16.1 20.1 88.2
Gearbox (Tonne) 37.3 38.2 36.8 36.4 36.4 -
Converter (Tonne) 3.3 6.3 3.1 6.3 3.1 6.3
Total drive-train (Tonne) 60.3 47.9 55.3 58.7 59.6 94.4
Data taken from UpWind
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Comparison of different wind turbine drive-trains
Gearbox 3G 3G 2G 1G 1G DD
Generator DFIG PMG BDFIG PMG BDFIG PMG
Cost (000 )
Generator construction 94 25 81 117 106 714
Converter 67 200 60 200 60 200
Electrical subsystem 190 189 190 190 190 189
Gearbox 373 382 304 218 218 -
Total drive-train cost 724 796 635 725 574 1103
Annual energy (MWh)
Generator losses 601 824 750 496 946 1021
Converter losses 254 792 261 809 261 810
Gearbox losses 919 919 689 460 459 -
Total losses 1774 2535 1700 1765 1666 1831
drive-train efficiency 92.5 89.3 92.8 92.5 93.0 92.3
Data taken from UpWind
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Efficiency Comparison
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Comparison of conventional high-speed DFIG with
medium-speed Brushless DFIG in a 5 MW Nacelle
2 stage gearbox
Cooling system
Brushless DFIG
Fractionally Rated Converter
No slip rings
Smaller Gearbox
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Conclusions

• Brushless DFIG steadily developed by Wind
  Technologies.
• Brushless DFIG is in operation in a 20 kW Wind
  Turbine at Cambridge.
• 250 kW Brushless DFIG built and tested with
  successful rated and fault ride-through results.
• Two medium-speed 5MW Brushless DFIGs designed to
  fit into medium-speed drive-trains with 1- or
  2-stage gearboxes.
• Performance of these drive-trains compared
  against high- medium-speed geared and direct
  architectures.
• Medium-speed Brushless DFIG drive-train is
  competitive with alternative designs in respect
  of weight, cost and efficiency and reduces
  drive-train CAPEX
• A large scale Brushless DFIG is practicable and
  scalable from current designs
• BDFIG drive-train appeared in Eize de Vries
  article Products of 2012 in January Issue of
  Wind Power Monthly ranked 2nd in Top Turbines for
  2012 in competition alongside GE Wind, Winergy,
  Emerson Romax.

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• Thank you