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EECElectrical Energy Conversion

18 March 2009

Possible solutions to overcome drawbacks of direct-drive

generators for large wind turbinesDeok-je Bang , Henk Polinder ,

Ghanshyam Shrestha , Jan Abraham Ferreira

Electrical Energy Conversion, DUWINDDelft University of Technology

The Netherlands

d.j.bang@tudelft.nl

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EEC

Increasing Wind Turbine power,

Direct-drive generator is large &

heavy.

Hence, it is expensive.

Background

mTP

For large direct-drive generators,

New configuration with high force density

and less material is required.

Hence, the cost reduction is achieved.

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Objective

• Find solutions of large direct-drive generators

Electromagnetic material

Structural material

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Contents

1. Promising solutions for large direct-drive

2. Challenges of large direct-drive

3. Rough design of new direct-drive PM

generators

4. Prototype (downscaled)

5. Summary

6. Further researches

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1. Promising solutions for large direct-drive (Source: Bang et al. 2008)

A.Active part• Permanent magnet synchronous generator

(PMSG)

B. Inactive part• Ring shaped construction of which air gap is

maintained by the bearingless drive

C. Practical issues• Modular construction for easy production,

handling and maintenance

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2. Challenges of large direct-driveA. Minimize inactive material

(1) New ring shaped construction

U-phase

V-phase

W-phase

U-phase

V-phase

W-phase

RotorU-phase

V-phase

W-phase

W-phase

V-phase

U-phase

Stator

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(2) New bearingless drive

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(1) Buoyant rotating partin order to

• Support heavy structure easily• Reduce structural material for supporting• Give flexibility in supporting and guiding heavy structure

B. New supporting and guiding concept

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(2) Hydrostatic bearingin order to

• Prevent the touchdown of rotor on stator• Maintain the air gap when the bearingless drive is in failure• Reduce a peak power consumption of the bearingless drive

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A

A’

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3. Rough design of new direct-drive PM generators: 5 & 10 MW

Turbine specification

Power 5 MW 10 MW

Speed 12.1 rpm

8.6 rpm

Rotor diameter 126 m 178 m

Rated wind speed 12 m/s 12 m/sGenerator

Air gap diameter 6.3 m 8.88 m

Air gap length 6.3 mm 8.88 mm

Force density 40 kN/m2

40 kN/m2

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A. Active mass

5 MW 10 MW

Copper 8.0 ton15.1 ton

Stator iron

21.8 ton

42.7 ton

Rotor iron

10.1 ton

20.9 ton

PM 3.2 ton 8.9 ton

Total 43.1 ton

87.6 ton

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B. Inactive mass

Assumption:• Max. normal pressure acting on rotor & stator is about 325 [kN/m2]

• Deflection < 10% of g• Deflection of stationary part is neglected

• th and tb of stationary part are the same with rotating part’s

for the deflection modelling of rotating part

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5 MW 10 MW

Rotor part 9 ton 62.4 ton

Stator part 10.6 ton 69.9 ton

Fluid (water)

13.4 ton 40.8 ton

Total 33 ton 173.1 ton

Modeling of rotor deflection:

Mass estimation:

IE

lwg h

384

505.0

4

max

b

b

AE

wlg

4

05.0max

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C. Total mass estimation

• Concept-1: EESG DD

(Enercon concept, m/T=66.5 kg/kNm at 4.5

MW)

• Concept-2: PMSG DD

(Zephyros concept, m/T=46.4 kg/kNm at 1.5

MW)

• Concept-3: PMSG DD

(Theoretical design, m/T=25 kg/kNm at 2, 3 &

5 MW)

• Concept-4: PMSG DD

(NewGen concept, m/T=18.4 kg/kNm at 4 MW)

• Concept-5: DFIG 3G

(DFIG concept, m/T=17.4 kg/kNm at 3.5(4)

MW)

Assumption: m/T of each concept is constant in

scaling up.

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5 MW 10 MW

Concept-1 262 ton 738.4 ton

Concept-2 183 ton 515.2 ton

Concept-3 98.7 ton 277.6 ton

New concept

76.1 ton

260.7 ton

Concept-4 72.6 ton 204.3 ton

Concept-5 68.7 ton 193.2 ton

In the rough design, general steel structure was used for inactive part construction. Therefore it is expected that the inactive mass can be reduced further by structural optimization.

• Generator mass comparison of different

concepts

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4. Prototype (downscaled): Sponsored by Wintech in Korea

Rotor

StatorRollers

• Modular construction (machine type: TFPM machine)

• Ring shaped construction

3ph_

1set

StatorRotor

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Power analyzer

Torque sensor

Rotor

Stator

Rollers

Gearbox

Driving Motor

Motor driving unit

Power analyzer

Torque sensor

Rotor

Stator

Rollers

Gearbox

Driving Motor

Motor driving unit

Driving motor

3ph AC machine

- Pn: 14.3 kW

- Nn: 2600 rpm

- Tn: 52.7 Nm

Pulley & Belt

- DPulley_1=6 in - DPulley_2=12 in

Gearbox 43:1 gear ratio

Pulley & Belt

• Experimental setup

Experimental analysis is going on.

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5. Summary• New direct-drive concepts have been proposed

with

- New bearingless drive concept

- New guiding/supporting concepts

• Rough design of new 5 & 10 MW direct-drive PM generators have been done

• Downscaled prototype has been built

- Structure: Ring shaped, doubled-sided AF machine

- Machine type: (TF)PM machine

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?

6. Further researches• Electromagnetic optimization• Detailed design on the new direct-drive concept• Structural mass minimization• Find sealing solution

Steel Al. profile

?

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Thanks for your attention !

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Back up slides

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Promising solutions for large direct-drive (Source: Bang et al. 2008)

A. Active part• Permanent magnet

synchronous generator (PMSG)

B. Inactive part• Ring shaped construction of

which air gap is maintained by the bearingless drive

C. Practical issues• Modular construction for easy

production, handling and maintenance

PM

Core

Winding

Secondary part

Primary part

Core

Source: Dubois (2004), Ph.D. Dissertation

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Strength of PM machine

• high energy yield and light weight

• no additional power supply for the

field excitation

• improvement in the efficiency

• higher reliability without slip rings

• higher power/weight ratio

compared to EE machines

Direct-drive permanent magnet synchronous generator (PMSG DD)

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Inactive part (proposed in 2008)

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Conventional bearingless drive

Concept with complicated winding and control

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New bearingless drive