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

Design and Performance Analysis of a 5 MW

Medium-Speed Brushless DFIG drive-train

Peter TavnerWind Technologies LtdPast President of European Academy of Wind Energy

Page 2 All information confidential to Wind Technologies Ltd

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.


Brushless DFIG drive-train

Gearbox

x3

Partially-rated

AC/AC

Generator

DFIG

Gearbox

x1 or x2

Partially-rated

AC/AC

Generator

B’DFIG

Page 4

Synchronous mode operation

Converter controls Real power Reactive power

21r pp

f5060n

Synchronous speed

Brushless DFIG Operation

Grid, 50Hz Fractionally rated frequency converter

Brushless Doubly-FedInduction Generator (BDFIG)

Stator control winding

Stator power winding

50HzX Hz


Why is Brushless Better?

DFIG Brushless DFIG

Converter Rating Partially-rated Partially-rated

No Brushes/Slip rings

Gearbox 3 stage 1 or 2 stage

Grid Compatible Partially Fully


History of the Brushless DFIG1902- 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


Wind Technologies Progression in Brushless DFIG sizes

20 kW Brushless DFIG Wind Turbine

Rated power

Hub height

Rotor diameter

Generator

Gearbox

Converter

Yaw

20 kW

12.5 m

11 m

Brushless DFIG

2 stage helical

Grid –connected, partially-rated

Free yaw, down-wind

West Cambridge Site, CambridgeIn operation from March 2009


Manufacturing process for 250 kW Brushless DFIG

2 winding stator,4 pole & 8 pole

1 winding rotor,6 pole


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


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 Unit

Natural Speed 300 88 rev/min

Speed Range 192-408 56-120 rev/min

Gearbox Ratio 27.7 7.25

Nominal Voltage 690 V

Grid Frequency 50 Hz

Rated Power 5 MW 5 MW MW

Rated Torque 121 416 kNm

Proposed 5 MW Brushless DFIG Design Specification


Design Process For Brushless DFIG

Coupled Circuit Analysis

System Dynamics

LVRT & Grid Connection

Controller Optimization

Thermal Modelling

Analytical Design Software


Equivalent Circuit

I1 R1 j1Lr Rr /s1 Ir R2s2s1 I2

s2s1 2Vj1Lm2j1Lm1nV1 1

n n n

n

n n

n

Parameter BDFIG_2G BDFIG_1G

R1 (mΩ) 4.2 5.12

R2’’ (mΩ) 4.2 5.18

Rr’ (mΩ) 6.8 38.14

Lm1 (mH) 18.05 7.68

Lm2’’ (mH) 12.46 6.89

Lr’ (mH) 3.14 6.84


Finite Element Analysis – Flux Distribution


5 MW Brushless DFIG DesignBDFIG_2G BDFIG_1G Units

SupplyGrid Voltage 690 VGrid Frequency 50 Hz

StatorPW Pole Number 4 32CW Pole Number 12 36Winding Configuration DeltaPW Full Load Current 1859 1940 ACW Full Load Current 760 801 AAirgap Diameter 2191 3800 mm

CommonRotor Pole Number 8 34Stack Length 631 761 mmElectrical Steel Grade 450/65 W/kg/mmSpeed range 192 - 408 56 – 120 rev/minTorque 121 416 kNmRated Power 5000 5000 kWEfficiency 96.6 95.7 %Total Active Mass 9.45 12.39 TonneRotor Inertia 11183 122110 kg.m2


High-speed 3-stage PMG/DFIG

Medium-speed

1- or 2-stagePMG/BDFIG

Direct Drive PMG

Drive-train Technologies

Architecture Gearbox Generator

AC

ACPMG

ACAC

DFIG

PMGAC

ACAC

AC

BDFIG

PMGAC

AC



Gearbox 3G 2G 1G DD

Generator DFIG* PMG* BDFIG PMG* BDFIG PMG*

Generator dimensions

Rated speed (rev/min) 1200 1200 410 107 107 14.8Airgap diameter (m) 0.84 0.84 2.2 3.6 3.8 7.5Stator length (m) 1.15 0.94 0.63 0.68 0.76 1.25Number of pole pairs 3 25 8/12 80 16/18 147

Weight

Generator (Tonne) 19.7 3.4 15.4 16.1 20.1 88.2Gearbox (Tonne) 37.3 38.2 36.8 36.4 36.4 -Converter (Tonne) 3.3 6.3 3.1 6.3 3.1 6.3Total drive-train (Tonne)

60.3 47.9 55.3 58.7 59.6 94.4

*Data taken from UpWind



Gearbox 3G 2G 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


Efficiency Comparison


Comparison of conventional high-speed DFIG with medium-speed Brushless DFIG in a 5 MW Nacelle

Smaller Gearbox

No slip rings

2 stage gearbox

Cooling system

Brushless DFIG Fractionally Rated Converter


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.

Thank you

Documents

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