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Superconducting Generators for Wind

Turbines

Abrahem Al-afandiHamad Almutawa

Majed AtaishiAdvisor & ClientDr. James McCalley

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Overview• Project Background. - What is it?- Why?• Objectives.• Approach Taken.• Suggested Designs.• Design Evaluation Methods.

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Project Background What is it?• Inland Direct-Drive Wind

Turbines.1. 5-MW PMSG.2. 10-MW HTS. Why Direct-Drive?• Integrated in nature.• Avoiding the need for large,

maintenance-intensive gearbox.

• Reduced size and weight.• Efficient & Reliable.

RPM

RPM

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Objectives• Suggested 5MW turbine using permanent magnet generator.• Suggested 10 MW turbine using high temperature

Superconductor generator.

Each suggested design has:1. To be Cost-effective.2. High Energy yield.3. Low weight and volume.4. Suitable cooling system.

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Our Approach• Top to bottom view of steps taken :

components & operation of Generator

Direct-Drive vs. Conventional

PMSG HTS

Different Topologies

Suggested Design 1

Materials

Different Topologie

sMaterials

Suggested Design 2

Designs Evaluation

Feasible for 5-MW

Feasible for 10-MW

Cost Analysis

Cost Analysis

Performance Attributes

Performance Attributes

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The DifferencePMSG HTS

Schematic layouts

HTS is lighter for higher

MW

Cooling Systems

Before Choosing Promising Designs

• There needs to be a balance among electrical, magnetic, thermal, mechanical, and economic factors for a well designed generator.

• These factors are always conflicting with each other. • No matter what kind of methods designers use to optimize,

the keys are:1. Low cost.2. High reliability and availability.3. High cost always prevents generators from

commercialization.In General, the better topology of DD generators has the maximum output, minimum expenses and highest

reliability.

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1. PMSG Topologies• Air Gap Orientation.1. Radial has relatively small diameter.2. Axial ha a compact design.

• Stator Core Orientation.3. Longitudinal is used in conventional designs.4. Transversal has less copper losses, diffi. To con.

• PM Orientation with respect to air-gap.5. Surface-Mounted PM is easer to construct.6. Flux- concentrating PM has higher remnant flux.

1.

2.

VS.

3.

4.

VS.

VS.5.

6.

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1. PMSG Topologies Cont.

• Copper Housing. 7. Slotted has a better retention of the armature windings, but has cogging torque. 8. Slot-less has low cogging torque.

• Iron Core VS. Coreless 9. Iron-Core has lamination losses and more weight.10. Coreless eliminates cogging torque and reduce weight.

VS.

7.

8.

9.

VS.

10.

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Two Possible PMSG Designs

Design 1Design

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• Radial-Longitudinal-Surface Mounted-Iron core-Slotted

Inner-rotor Outer-rotor

Simple Construction

Accommodates multi-pole structure due to larger rotor periphery.

Good Utilization of active materials

With stands demagnetization

Relatively Smaller diameter

Avoids the increase in mass,

Better torque density

Outer-rotor Double-rotor

Reduced weight due to high no. of poles

Simple Stator construction.

Reduced Yoke thickness and armature overhang.

Compact.

No Cogging torque No vibrations

Less iron losses and has a greater efficiency

Axial-Longitudinal-Surface Mounted- Coreless- Slot-less

• Axial machines are not suited for MW power ratings, since the outer radius becomes larger, and the mechanical dynamic balance must be

taken into consideration.

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PMSG Materials• Three PM materials were investigated.

Good Material to be used

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2. HTS Topologies

• Partially VS. fully superconductor.• Axial VS. Radial flux.• Air-core VS. Iron-core

Fully VS. Partially

Fully PartiallyStrengths Weaknesses

Highest power density

High AC losses

Almost ½ the mass of partially SC

Complicated cooling system (needs high power)

Smaller air-gap Increase the use of HTS> high cost.

Strengths WeaknessesExpected low AC loss (Damper shell)

Air-gap is relatively large(using thermal Isolation

Low cost ( SC only in field winding)

Increased weight

Rotating sealing(only with rotating field)

Partially is dominant until a breakthrough in AC losses is made

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Axial VS. Radial

Axial RadialStrengths WeaknessesHigh power per unit volume

Lower torque to mass ratio

Shorter than radial Structurally unstable when diameter is large

Compact Heavier than radial machines.

Strengths WeaknessesSuitable for MW DD due to large diameter.

Lower torque to volume ratio

Widely used in wind project. Simple Mech. Structure easier to be made stable enough.

Suitable for MW class

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Air-core VS. Iron-core

Air-core Iron coreStrengths Weaknesses Popular for 10 MW SCDD

Reluctance in magnetic circuit increases > more HTS wires needed > high cost

Reduce Weight For 10KW>7.5km

Better transient stability (sy. Reac. Smaller)

Higher peak torque and current when short circuit faults occur.

For stator: better cooling scheme, no cogging torque, small air gap flux harmonics, reduce vibration, better insulation but causes cooling difficulty

EMF acts directly on HTS coils > limits performance.

Strengths WeaknessLess HTS wires>less cost Presence of iron

increases rotor mass.

Better SC coil performances & higher sync. Reactance.

Subject to eddy current losses.

For 100KW> 2.6 km For stator: iron teeth brings unwanted teeth harmonics.

For stator: possible to use iron teeth with less losses due to low freq. 10hz. Can reduce cost of HTS

For Stator: Highly saturated. Offers robust mechanical support for armature windings. Less comp

For Stator: Highly saturated. Offers robust mechanical support for armature windings. Less complicated. Less expensive.

For Stator: cogging torque. Promising

if HTS price goes

down

Better performan

ce

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HTS Material

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Recommended Design 1• 5-MW PMSG wind Generator: Radial

Inner-rotor Outer-

rotor

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Recommended Design 2• 10 MW SCDD Wind Generator:• Partially SC with HTS field winding on the rotor.• Stationary armature windings.• Radial flux machine. • Iron-cored rotor with iron teeth stator winding.

From AMSC

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Performance AttributesA good design

should not only have high torque density,

but it has to have a low cost/torque

ratio.

This picture shows that RFPM has a relatively low Torque density.

This picture shows that RFPM has the lowest cost/torque ratio. (good)

Comparison table

Cost Analysis Model• Existing model From the National renewable

energy lab.• The purpose of the model is to calculate ICC, AOE.• The Model is valid for: 1-Power range from 0.75MW - 5MW. 2-Rotor diameter: 80m-120m.• It is valid for extrapolation for

power output up to 10MW and rotor diameter of 200m.

VariablesFor cost evaluation we need to get:• AEP(Annual Energy production).• ICC(initial capital cost).• AOE(Annual operating expenses).• FCR(Fixed charge rate).• COE(Cost of Energy).

AEP• AEP = CF(capacity factor) * rated power * 8760

hours• The capacity factor varies depending on the wind

farm.- AEP for 5MW generator is = 13.14GWh.- AEP for 10MW generator is = 26.28GWh.- The uncertainty percentage is:- +/- 0.02 for 5MW generator. - +/- 0.05 for 10MW generator.

Generator 5 MW 10 MW

AEP 13140 MWh

26280 MWh

ICC (total) 5583.62k $ 25510.96k $

AOE 145.4k $ 290.6k $

COE 0.061 $/KWh +/- 0.05

0.13 $/KWh+/- 0.09

Calculated Results

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Design evaluation Methods

We were given 4 ways to evaluate our designs:

1- Evaluation using proper software. ✖2- Hardware evaluation. ✖3- Literature review. ✔ - Technical papers. - IEEE articles and researches.4- Industry experts. ✔ - AMSC(HTS). - ABB & Gamesa(PMSG).

Cost Analysis Evaluation

Validating AEP:

COE in $/KWh for different power ratings and diameters:

Cost Estimation

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Remarks• Wind turbines are growing in

power capacity with each new generation.

• Wind farm economics is demanding increased reliability to minimize cost and maximize productivity.

• More power per tower.

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Question?