Dr. Longya Xu The Ohio State University April, 2010.

2MW PM Machine Design for Direct–Driven Wind Turbine

Generator Application

Dr. Longya XuThe Ohio State University

April, 2010

Contents1. Introduction Major Wind Power System Configurations Challenges to Remain in Power Grid Why PM Direct-Driven WTG Getting Popular

2. Initial Design and Performance Analysis

Specifications and Sizing Stator and Rotor Design Performance Evaluation

3. Conclusions

1.2 Major Wind Power Generation System Configurations

Example: Windformer (ABB)

Capacity Trajectory of Single Unit

Off-Shore Wind Farm Based on HVDC

Multi Units connected in series and power transmitted through HVDC

Specifications and Sizing

V Rated(V, rms) 690 Frequency 5~11Hz

I Rated(A, rms) 1700 Speed 10~22 rpm

KW Rated 2,000 Torque (peak) 850kNm

The reason for low speed at:10~22 rpm

Tip Speed of Wind Blades: vtip = 115 meters/sec.

The reason for low Frequency at:5~11 hz

Sizing Equations

LDT rre2

Consider the electrical and magnetic loadings are relatively constant, we have a traditional sizing equation:

where subscript “r” indicates rotor related variables.

(1)

In (1) the electrical loading refers the current along the air-gap in the unit of Ampere per Meter (A/M).The magnetic loading refers the magnetic flux density passing through air-gap in the unit of Tesla.

Sizing Equation Alternative

LDTe300

where subscript “o” indicates the stator related variables and a coefficient proportion to the current density and magnetic flux density. Here current density is in the unit of Ampere per Square Meter and magnetic flux density in Tesla.

0

0

(2)

0 LD30

is also closely Do/Dr related and at certain value of Do/Dr, is maximized, or minimized.

Combining (1) and (2), we have two new sizing equations, one in terms of stator OD

LDTe5.2

0'0

LDT rre5.2'

(3)

(4)

another in terms of rotor OD

In sizing an electric machine, the new equations take many variables into

consideration: electrical loading, magnetic loading, Do/Dr ratio, and slot current density.

Stator OD 3820mm Pole # 60

Stator ID 3500mm Slot # 288

Stack L 1300mm Air-gap 6mm

Sizing Results

21x120

R1750

R1910

Stack l ength: 1300Ai rgap: 6

Stator Slot Shape and Dimensions

Stator current density at 2 MW

17.2

12

782

4

0.77(A/mm2)

Considerations on Slot Numbers

360 Slots: Integer Number/Pole/Phase

288 Slots: Fractional Number/Pole/Phase

Pros: reduced slot harmonics and cogging torque

Cons: reduced fundamentals and less effective in EM conversion

Pros: increased fundamentals and more effective EM energy conversion

Cons: more slot harmonics and increased cogging torque possibility

Considerations on Inner or Outer Rotor

Inner Rotor

Outer Rotor

Pros: traditional mechanical structure to design and manufacture

Cons: extra effort to install permanent magnets

Pros: easy installation of permanent magnets and better utilization of space

Cons: non-traditional mechanical structure and extra effort for bearing installation

Estimation of Losses and Efficiency

Estimated Copper Losses

Pcu= 3I2R = 2.7~3 kw

Assume equal amount of iron and other losses

Effi. = 97%

Expected energy efficiency

PFe+other = ~3 kw

FEM Comparison Results

(1) Outer Rotor with 360 Stator Slots

In order to keep copper losses the same in comparison, some changes are made as follows:• Cross-section of stator slot for conductor:

1400mm2 (288 slots) vs. 1120mm2 1400*288/360 (360 slots)

• Current (peak) flow in each conductor: 1300A(288 slots) vs.

1040A (360 slots)1300*8/10

FEM Comparison Results

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00Time [ms]

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

20.00

Y1

[Wb

]

Ansoft Corporation Outer rotor3XY Plot 1

Curve Info

FluxLinkage(WindingA)Setup2 : Transient

FluxLinkage(WindingB)Setup2 : Transient

FluxLinkage(WindingC)Setup2 : Transient

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00Time [ms]

-800.00

-600.00

-400.00

-200.00

0.00

200.00

400.00

600.00

800.00

Mo

vin

g1

.To

rqu

e [k

Ne

wto

nM

ete

r]

Ansoft Corporation Outer rotor3XY Plot 5

Curve Info

Moving1.TorqueSetup2 : Transient

Torque Production

Winding Flux

Linkage

(1) Outer Rotor with 360 Stator Slots

(2) Outer Rotor with 288 Stator Slots

FEM Comparison Results

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00Time [ms]

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

Y1

[Wb

]

Ansoft Corporation Outer rotorXY Plot 1

Curve Info

FluxLinkage(WindingA)Setup2 : Transient

FluxLinkage(WindingB)Setup2 : Transient

FluxLinkage(WindingC)Setup2 : Transient

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00Time [ms]

-800.00

-600.00

-400.00

-200.00

0.00

200.00

400.00

600.00

800.00

Mo

vin

g1

.To

rqu

e [k

Ne

wto

nM

ete

r]

Ansoft Corporation Outer rotorXY Plot 5

Curve Info

Moving1.TorqueSetup2 : Transient

Winding Flux

Linkage

Torque Production

(2) Outer Rotor with 288 Stator Slots

(3) Inner Rotor with 360 Stator Slots

FEM Comparison Results

Winding Flux

Linkage

Torque Production

0.00 20.00 40.00 60.00 80.00 100.00 120.00Time [ms]

-20.00

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

20.00

Y1

[Wb

]

Ansoft Corporation Innerrotor1XY Plot 2

Curve Info

FluxLinkage(Winding1)Setup1 : Transient

FluxLinkage(Winding2)Setup1 : Transient

FluxLinkage(Winding3)Setup1 : Transient

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00Time [ms]

-800.00

-600.00

-400.00

-200.00

0.00

200.00

400.00

600.00

800.00

Mo

vin

g1

.To

rqu

e [k

Ne

wto

nM

ete

r]

Ansoft LLC Innerrotor1XY Plot 1

Curve Info

Moving1.TorqueSetup1 : Transient

(3) Inner Rotor with 360 Stator Slots

(4) Inner Rotor with 288 Stator Slots

FEM Comparison Results

Winding Flux

Linkage

Torque Production

(4) Inner Rotor with 288 Stator Slots

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00Time [ms]

-15.00

-10.00

-5.00

0.00

5.00

10.00

15.00

Y1

[Wb

]

Ansoft LLC InnerrotorXY Plot 3

Curve Info

FluxLinkage(WindingA)Setup1 : Transient

FluxLinkage(WindingB)Setup1 : Transient

FluxLinkage(WindingC)Setup1 : Transient

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00Time [ms]

-800.00

-600.00

-400.00

-200.00

0.00

200.00

400.00

600.00

800.00

Mo

vin

g1

.To

rqu

e [k

Ne

wto

nM

ete

r]

Ansoft LLC InnerrotorXY Plot 1

Curve Info

Moving1.TorqueSetup1 : Transient

3. Conclusions• PM machine plays a critical role in WTG systems

• Direct-driven WTG requires a large size machine and heavy use of permanent magnet

• Optimal sizing of PM machine is significant

• Two rotor structures are possible• Slot/phase/pole fractional or integer

makes differences• FEM comparison results are

presented• Design of PM machine satisfying

specifications is achieved.

Thanks!

Q & A