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
Christopher Haller
Graduate Research Assistant
Oregon State University
Hai-Yue Han
Graduate Research Assistant
Oregon State University
Dr. Annette von Jouanne, Ph.D. P.E.
Professor
Oregon State University
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.