Direct-Drive Rotary Generator Design by Genetic Algorithm for Ocean Wave Energy Application

Research Conducted: June - September 2009 Presentation: October 5, 2009

Dr. Ted K.A. Brekken, Ph.D.

Assistant Professor

Oregon State University

brekken@eecs.oregonstate.edu

Christopher Haller

Graduate Research Assistant

Oregon State University

haller@eecs.oregonstate.edu

Hai-Yue Han

Graduate Research Assistant

Oregon State University

haiyuehan@gmail.com

Dr. Annette von Jouanne, Ph.D. P.E.

Professor

Oregon State University

avj@eecs.oregonstate.com

Presentation Outline

1. Wave Energy Background

2. Design Considerations

3. Mechanical Layout

4. Time Domain Electromagnetic Analysis

5. Conclusion

Wave Energy Background

• 11 foot spar

• 4 foot diameter float

• Designed for water depth

of 135 feet

2007 10kW Seabeav I

2007 10kW Seabeav I

Preparing for sea trial

in Newport

[5]

2007 10kW Seabeav I – Sea Trial

2008 10kW L-10

• 25 feet tall, 11 feet wide

•Direct Drive

Integrated Linear Generator

No pneumatics or hydraulics

• Developed in collaboration

with C.P.T. and the Navy

2008 10kW L10 – Sea Trial

OSU Facilities to Advance Wave Power

O.H. Hinsdale Wave Research Lab

(HWRL)

Wallace Energy Systems and Renewables Facility

(WESRF)

OSU – Key Location for Wave Power Research• 750 KVA Adjustable Power Supply

• Variable Voltage input(0-600Vac), 600A• 3-phase adjustable (while loaded) for

balanced and unbalanced testing• Highest Power University Lab in the

Nation• Enables Multi-Scale energy research

• Four Quadrant Dynamometer • Programmable torque/speed• Dynamic Vector Controls 0-4000 rpm

• Bidirectional Grid Interface • Regeneration back to the utility grid

• Flexible, 300 hp,Motor/Generator test-bed

• 120KVA programmable source• Transient VLrms=680V• Steady State VLrms= 530V• Frequency range: 45Hz to 2KHz

• 10 kW Linear Test Bed• 2 m/s, 10 kN• 1 ms/, 20 kN

Wallace Energy Systems and Renewables Facility (WESRF)

Why Wave Energy?

[2,3,4]

• Wind Energy → 587 W/m2 with 8 m/s mean

distribution of wind speed

• Solar Energy → 200 W/m2 Year Round Average

• Wave Energy → 30kW/m Year-Round-Average Available

Why Wave Energy?

Wave Power Density in Kilowatts per Meter [kW/m][1]

Design Considerations

Design Considerations

• Low Speed Operation (5 rpm)

• Reciprocating Rotary Design

• High Torque Load

• Caustic Ocean Environment

• Serviceability Complications

Top Level Design Choices

Machines Considered

• PMAC

• Doubly Fed Induction

• Induction

• Reluctance

• Vernier Hybrid

Characteristics

• Axial / Radial

• Super Conductor

• Crescent Shaped

• Air / Iron Core

Mechanical Layout

Single Coil & C-Core Structure

Three-Phase Coil Configuration

Cross-Sectional Top-Down View

Single Layer Structure

Top Level Machine Structure

Floating Machine Structure

Time Domain Electromagnetic

Analysis

Simplified Magnetic Circuit

Calculation Methods

• Magnetic Circuit Analysis

• Magnetic Shear Line to

2nd Quadrant B-H

Operation intercept

Initial Motor Chromosome

Primary Gene Set

1 Radius of Machine

2 Length of One Side of C-Core

3 Distance Across Air Gap

4 Cross-Sectional Area of Magnets

5 Length of Magnets

6 Thickness of Magnets

7 Wire Turns

8 Wire Gauge

9 Machine Layers

Initial Genetic Algorithm• Initial population created.

• Population doubled.

• Random cross breeding between 1st and 2nd population set

• Random mutations w/ fixed-rate / fixed-probability (quantity)

• All genes saturation checked / adjusted.

• Fitness of chromosomes evaluated, sorted from best to worst.

• Worst ½ of chromosomes discarded, repeat back to doubling.

• Best motor tracked throughout process.

Refined Generator Chromosome

Simplified / Refined Gene Set

1 Magnet Width

2 Magnet Length

3 Magnet Thickness

4 Air Gap Distance

5 Wire Gauge

Time Domain RefinementSimplified GA Variables

1 Magnet Width

2 Magnet Length

3 Magnet Height

4 Air Gap Distance

5 Wire Gauge

• Maximum allowable turns

in air-gap.

• Steel thickness based upon

allowed flux density.

• Many safety/saturation

checks removed.

• Processing speed 4.3 times

faster than previous model.

Genetic Algorithm Cost Functions

• -Total Power

• -Total Power, -Efficiency, +Steel Volume

• -Total Power, -Efficiency, + Total Mass, +AWG, +Wire Turns

• -Total Power, Efficiency, +Total Mass, +AWG Size, Wire Turns

Used for final evaluation:

• -Total Power, -Efficiency, +Total Mass, +Magnet Volume

{Negative numbers indicate a “more fit” machine}

Parametric Sweep of 5 Genes

• Swept 25 steps nested sweep.

• 9,765,625 evaluations.

• 1.5x the run time of the

refined (2nd) design, 2.8x slower

run time of original design (1st).

• Evaluated with GA cost

function for fitness.

• Results different from GA.

Results

GA vs. Sweep ResultsVariable GA Sweep Units

1 Magnet Width .0020 0.0063 [m]

2 Magnet Length .1157 0.2990 [m]

3 Magnet Height .0254 0.0244 [m]

4 Air Gap Distance

.0034 0.0200 [m]

5 Wire Gauge 20 19 AWG

Characteristics GA Sweep Units

  Open EMF (per coil) 0.258 122 [V]

Current (per coil, @ 2.5 [A / mm2]) 1.294 1.632 [A]

Single Layer Total Power 9 1843 [W]

Efficiency (from R. loss) 94 87 [%]

Single Layer Mass 20 811 [kg]

Coil Turns 1 319 qty

Torque (per wheel) 18.5g 4192 [Nm]

Finite Element Analysis

Conclusion

Conclusions & Future Work

Conclusions:

• 5 [rpm] generator is feasible.

• Generator possible, but heavy.

• Weight and slow speed lead to issue of cost.

Future Work Direction:

• Examine larger variety of motor topologies.

• Perform more in-depth cost analysis.

• Refinements to manufacturability.

Bibliography[1] http://www.geni.org/globalenergy/library/renewable-energy-resources/ocean.shtml Global Energy Network Institute

[2] http://blogs.mysanantonio.com/weblogs/clockingin/wind%20turbine.jpg

[3] http://venturebeat.com/wp-content/uploads/2009/07/solar-panel-1.jpg

[4] http://eecs.oregonstate.edu/wesrf/projects/images/Wave%20Energy_Final.ppt

[5] Steven Ernst. Personal interview, 2009. Oregon State University.

[6] Duane C. Hanselman. Brushless Permanent-Magnet Motor Design, 1994.

[7] Magcraft. Permanent magnet selection and design handbook. National Imports,

April 2007.

[8] Ned Mohan. Electric Drives: An Integrative Approach, 2003.

[9] Joseph Prudell. Email, 2009. Oregon State University.

[10]Joseph Prudell. Novel design and implementation of a permanent magnet linear

tubular generator for ocean wave energy conversion, 2007. Thesis for Master of

Science.

[11] P.C. Sen. Principles of Electric Machines and Power Electronics, 1997.

[12] Mueller & McDonald. A Lightweight Low Speed Permanent Magnet Electrical Gen-

erator for Direct-Drive Wind Turbines, 2008.

Acknowledgement

Thanks to Grainger Center for Electric Machinery and Electromechanics for

supporting this research.