Multi-Objective Optimization of an Actively Shielded...
Transcript of Multi-Objective Optimization of an Actively Shielded...
Multi-Objective Optimization of an Actively
Shielded Superconducting Field Winding
David Loder
Dr. Kiruba Haran
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Outline
Design Concept
Field Computation
Optimization Scheme– Constraints
– Design Space
– Fitness Formulation
Results & Validation
Conclusions
Future Work
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Background & Motivation
Demand for high power density
Air-core superconducting machines
Containment of magnetic fields
– Eddy Current Shields [1]
– Magnetic Shields (steel)
– Active Shielding [2]
Fig.1. Actively Shielded Air-Core Superconducting Machine
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Design Concept
Fig.2. Cross Section Flux Density
Fig.3. Main Coils Only Excited
Fig.4. All Field Coils Excited 4
Field Computation
Fig.5. Radial Flux Density along D-axis Fig.6. Radial Flux Density at Armature
2-D Simplification of Biot-Savart (1)
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Superconducting Constraints
Fig.7. Flux Density in Main Coil
Fig. 8. Nb3Sn Critical Surface [3]
HyperTech T1505 Wires Selected
50% Safety Margin included
0.1% Strain Allowance6
Input θWinding
Geometry Valid?
Armature flux density met?
Within critical surface?
Assign small fitness
Compute Fitness (3)
Return fitness
Increasing Computational
Intensity
No
No
No
Yes
Yes
Yes
Fig.10. Fitness Formulation
Fitness Vector (3)
Define fitness to:– Maximize shielding
– Minimize coil usage
Bmax contained by stator (to below 0.5 mT): 35 mT
[5]
Min. fundamental of radial armature flux density: 2 T
Optimization Scheme: Evolutionary Algorithm [4]
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Preliminary Results
Fig.11. Pareto-Optimal Front
Design #39 vs. Optimized Uncompensated– 32 % ↓ Rmin
– 33% ↑ Coil Usage9
Validation
Fig.12. Design #39 FEA
Armature flux density: 6% error
Main coil peak flux density: 2% error
Fig.13. Operating Points [6]
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Conclusions
Combined shielding
– 97% Reduction in stator yoke
– 27% increase in coil usage
– Main coil peak field ↓ 5%
Fig.14. Passive Shielding Fig.15. Combined Active/Passive Shielding
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Stator Yoke
Future Work
Include End Windings
Include Stator Yoke in Optimization
Expand design space
– Pole Count
– Armature
– Stator Yoke
Incorporate manufacturing considerations in winding geometry constraints [7]
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[1] H. Woodson, “Eddy-current shield superconducting machine,” U.S. Patent 3772543 A, Nov 13, 1973.J. Clerk Maxwell, A Treatise on E lectricity and Magnetism, 3rd ed., vol. 2. Oxford: Clarendon, 1892, pp.68–73.
[2] M. Steckner and B.C. Breneman, “MRI magnet and MRI system with optimized fringe, fields, attractive forces and spatial constraints,” U.S. Patent 8729899 B2, May 20, 2014.
[3] J.W. Ekin, “Four dimensional JBT critical surface for superconductors,” J. Appl. Phys., vol. 54, no. 1, pp. 303-306, Sep. 29, 1982.
[4] S.D. Sudhoff, “Optimization-Based Design,” in Power Magnetic Devices: A Multi-Objective Design Approach. Hoboken, New Jersey: Wiley, 2014.
[5] ICNIRP, “Guideline to limits of exposure to static magnetic fields,” Health Phys., vol. 66, pp. 113-122, 1994.
[6] M.D. Sumption, S. Bhartiya, C. Kovacks, et. al., “Critical current density and stability of Tube Type Nb3Sn conductors,” Cryogenics, vol. 52, no. 2-3, pp. 91-99, Dec. 22, 2011.
[7] W. Stautner, K. Sivasubramaniam, S. Mine, J. Rochford, E. Budesheim, and K. Amm, “A cryo-free 10 T high-field magnet system for a novel superconducting application,” IEEE Trans. Aplied Superconductivity, vol. 21, pp. 2225-2228, Jun. 2011.
References