From Solar Airplanes to Carbon Nanotubes and Wires ... Nanotubes and Wires – Opportunities for the Coil Winding and Electric Machine Industries? Dan M. Ionel, Ph.D., IEEE Fellow

SPARK Introduction | February, 2016 | 1

From Solar Airplanes toCarbon Nanotubes and Wires –

Opportunities for the Coil Winding andElectric Machine Industries?

Dan M. Ionel, Ph.D., IEEE [email protected]

CWIEME Chicago, October 6, 2016

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Carbon Nanotubes and Wires for Electric Machines | CWIEME Chicago, Oct 2016 | 2/34

Abstract

The presentation introduces recent developments for carbon nanotubes (CNT) wire technology and electric machine design from University of Kentucky and collaborators. The advantages of CNT in terms of low specific mass and thermal conductivity are discussed together with advancements on improving their electrical conductivity. Inspired from the early developments of an EU stratospheric unmanned solar airplane, which required very light engines, a special brushless PM axial flux coreless multi-disc motor topology is proposed to serve as a benchmark for systematically comparing designs with conventional (copper or aluminum) and with CNT windings, respectively. It is shown that for the topology considered the CNT motors maybe superior in terms of light weight, especially for high speed applications. The possible opportunities generated by the new material and technology developments for the coil winding and electric machines industries and for products ranging from inductors for power electronics to single-phase fractional horsepower induction motors are discussed. The presentation includes a brief review of the latest research initiatives for the next generation of electric machines supported by the US Department of Energy.

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Dr. Dan M. Ionel

Dan M. Ionel is Professor of Electrical Engineering and L. Stanley Pigman Chair in Power at University of Kentucky in Lexington, KY. Previously, he held dual appointments in industry, as Chief Engineer with Regal Beloit Corp and before as Chief Scientist with Vestas Wind Turbines, and in academia, as Visiting and Research Professor with University of Wisconsin and Marquette University in Milwaukee, WI.

Dr. Ionel has more than 25 years of engineering experience and has designed electric machines and drives with power ratings between 0.002 and 10,000hp. He holds more than 30 patents and has published more than 100 journal and conference papers, including two winners of IEEE best paper awards. Dr. Ionel is an IEEE Fellow, the Chair of the IEEE Power and Energy Society Electric Motor Subcommittee, and the General Chair of the 2017 anniversary edition of the IEEE IEMDC Conference.

[email protected]

mailto:[email protected]

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SPARK and PEIK at University of Kentucky (UK)

• UK enjoys a longstanding tradition in electric machines and drives• Early developments on linear and PM motors, and vector control• Many learned machines using the Nasar and Boldea classic books

• PEIK - Power and Energy Institute of Kentucky, launched with large DOE grant in 2010• Core faculty in electric power engineering and many others in related fields• Endowment established and inaugural L. Stanley Pigman Chair started in 2015• On-going research on electric machines and drives, power electronics and systems,

renewable and alternative energy technologies• SPARK and other laboratories; faculty: 10+; graduate research students: 40+• Center for Applied Energy Research (CAER) at UK and ANSYS Inc. strategic partnerships.

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Center for Applied Energy Research (CAER) and ANSYS

Center for Applied Energy Research (CAER)• Established in 1975• One of University of Kentucky’s largest,

stand-alone, multidisciplinary research centers with more than 100 staff

• Fiber Development Laboratory with the largest solution spinning line found in an academic setting in North America

• Renowned research program on nanocarbon composites

ANSYS Inc.• The world’s largest simulation software

company• Multi-physics software• State of the art PC workstations and HPC large

scale system at UK.

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Outline

•Introduction

•Carbon nanotube materials

•Solar airplanes

•Benchmark electric machine - multi-disc coreless AFPM

motor

•Parametric design studies

•Comparative results

•Conclusion.

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• Individual carbon nanotubes (CNT) can have a conductivity up to 100 MS/m and very low mass density

• Conductivity substantially decreases when individual CNTs are assembled to form macroscopic conductors

• Conductivity may be enhanced by plating nanotubes with copper (Cu)

• Macroscopic CNT conductors also have negligible skin effect.

Material Conductivity(MS/m)

Density (kg/𝒎𝟑)

Temp. coeff. of resistance (/k)

Copper 58.0 8690 0.0038

Aluminum 35.0 2700 0.0043

CNT wire 1 (worst case) 2.4 1500 0.0015

CNT wire 2 (best case) 10.0 1500 0.0015

Carbon-Nano Tube (CNT) Material for Wires

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Fiber Development Laboratory at University of Kentucky (UK)

• Part of the large Center for Applied Energy Research (CAER)

• Largest solution spinning line found in an academic setting in North America.

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MWCNTs

Cu-plated MWCNTs

Bore dispersion

Alignment by drawing

Cu-MWCNT conductor core wire

Cu-plated Aligned MWCNT Wires

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CNT Demonstrations for Electromagnetic Devices

• Only couple of groups reported work on using CNT wires for electromagnetic devices, including electric machines

• Use of CNT wires in a high frequency transformer• Has higher resistance than its counterpart with copper windings• Performed as expected over a wide frequency range

• CNT wires have been demonstrated in a small PM synchronous motor• Concentrated coils• Rated for 30 W at 15,000 rpm• Efficiency of approximately 69%.

Transformer with CNT coils [3] Fractional slot PMSM with CNT coils [4]

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US DOE Research Program for NCT Wires and Machines

High performance conductors to minimize losses in the stator windings

• To be demonstrated on a 28 AWG NCT round wire with 1 m length

• Minimum of 33% reduction in I2R losses per unit weight or volume over a 28 AWG round copper or Al wire at 1500C

• Use the new wire to demonstrate a 1 hp single phase induction motor, including windings with electric insulation.

Source: US DOE-FOA-0001467, Next Generation Electric Machines: Enabling Technologies, 2016.

Photo courtesy of Regal Beloit Corp.

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Solar Airplanes

• The 80’s – the solar-powered Gossamer Penguin featured a 71-foot wingspan and a weight of 68 lb without the pilot. (Source: Design News Magazine)

• NASA Centurion (1999) and Helios (2003)

• See also André Noth, ”Design of Solar Powered Airplanes for Continuous Flight”, PhD Dissertation, ETH Zurich, 2008

• Latest news about perpetual solar flight

• … and the UK Solar Car – Gato Del Sol…

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Coreless AFPM for Solar Airplanes

• A coreless AFPM machine was originally developed for the EU stratospheric unmanned aircraft propulsion project at the University of Bath, England.

• The 90’s and 00’s – Heliplat, a Solar Powered Flying Platform for Telecommunications Applications [5]

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Multi-Disc Coreless Axial Flux Permanent Magnet (AFPM) Motor

• Multiple stator modules and rotor discs

• Coreless stator with coils and a light supporting structure

• Coils account for a significant proportion of the total weight of the machine

• Air-gap concentrated windings – considerable AC loss in the windings

• PM rotor.

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Number of rotor stacks 4

Number of poles 16

Number of stator stacks 3

Number of coils 12

3D Parametric Model

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Main Parameters for the Geometry

𝑳𝒂𝑷𝑴𝒊

𝑳𝒂𝒈

𝑳𝒂𝑷𝑴𝒐

𝑮𝑷𝑴𝑳𝒓

𝑳𝒔

𝑹𝒊𝒓𝑹𝒐𝒓

𝑹𝒊𝒔

𝑹𝒐𝒔

𝑾𝒄

𝑮𝒄

Parameter Value

𝑅𝑖𝑟 130.5 mm

𝑅𝑜𝑟 145 mm

𝑅𝑖𝑠 118 mm

𝑅𝑜𝑠 145 mm

𝐿𝑎𝑃𝑀𝑖 8 mm

𝐿𝑎𝑃𝑀𝑜 4 mm

𝐿𝑠 7 mm

𝐿𝑟 4 mm

𝐿𝑎𝑔 1 mm

𝑊𝑃𝑀 10.5 mm

𝑊𝑐 30 mm

𝐺𝑃𝑀 1 deg

𝐺𝑐 2 mm

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3D FEA Mesh

• Total number of elements: 414822

• Assigned mesh operations:

• Inside selection: PMs and back irons

• On selection: band surfaces facing PMs

Band object

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• Phase A coil terminals:BC

• Load Analysis: Instantaneous torque – ripple free in line with expectations.

• Open Circuit Analysis – EMF is sinusoidal as expected

Electromagnetic Field, Back EMF, and Torque

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• Airgap flux density

• Airgap flux density harmonic spectrum

Open-Circuit Analysis

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• Phase A coil terminals:BC

• Instantaneous torque

• Current density

Phase B

Current Excitation—Load Analysis

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• Airgap flux density due to armature reaction

• Harmonics cause losses in the PMs (and the rotor core)

• This can be mitigated by use of a special winding arrangements.

Load Analysis

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Multilayer Winding Arrangement

• Nearly sinusoidal air-gap flux density distribution is achieved by the use of the multi-layer winding arrangement

• This reduces loss in the PMs and rotor back

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Eddy Currents in the PMs

PM eddy current density distribution for a single layer winding (left), and a four layer winding (right). Maximum values for single layer and four layer winding are 3.26 A/m^2 and 2.01 A/m^2, respectively.

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Using CNT Instead of Copper Wire

Scaling methodology: Same loss/conductor volume for copper and CNT machines.

𝑃𝑒𝑚 ∝ 𝐷𝑜3 𝜎 𝐿

𝜎𝐶𝑁𝑇 ≪ 𝜎𝑐𝑜𝑝𝑝𝑒𝑟

• Increasing the number of stacks

• Increasing the axial length of the stator

• Increasing the diameter.

Compensate for reduction in power by

CNTCNToCNTCuCuoCu LDLD 33

CNTCuLet 5

oCuoCNT DD :1 Case

CuCu

CNT

CuCuCNT LLLL 236.25

oCuoCNT LL :2 Case

30.156

1

oCuoCNT DD

For the same EM Power,

Volume increases 2.23 times

Volume only increases 1.7 times

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Copper coils with 3 stator stacks

CNT material coils (worst conductivity) with 8 stator stacks and 0.375 times the current density.

CNT material coils (best conductivity) with 4 stator stacks and 0.78 times the current density.

Comparative Study 1: Increasing the Number of Stacks • The number of stacks is increased, such that:

• Loss/dissipation unit area for copper and CNT is the same• Torque is the same for all cases

• Achieved by in the CNT based design by:• Reducing current density per stator stack to reduce loss• Increasing the number of stacks to increase dissipation area, and compensate for

reduction in torque• Below: Example scaling at 1,000 rpm.

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CNT material coils (worst conductivity) with 2.8 times larger 𝐿𝑠𝑡𝑎𝑡𝑜𝑟 and 𝐿𝑃𝑀 and 0.35 times current density

CNT material coils (best conductivity) with 1.3 times larger 𝐿𝑠𝑡𝑎𝑡𝑜𝑟 and 𝐿𝑃𝑀,

and 0.76 times current density

Comparative Study 2: Increasing Stator Axial Length

• Constraints – equal torque and loss per unit dissipation area• Achieved in the CNT based design by:

• Increasing the axial length of the coils• This reduces the current density, (as coil area increases), and increases

dissipation area due to increase in length. Current is maintained the same. • The PM volume needs to be increased to compensate for the increased

reluctance of the magnetic circuit.

Copper

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Copper based machine CNT based machine with increased axial length

Coils

PMs

Back iron

Comparative Study 2: Increasing Stator Axial Length

Two-dimensional finite element analysis is utilized in order to find out the increase in PM thickness required to compensate for the higher air-gap reluctance.

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Comparative Study 3: Increasing Diameter Equal torque and loss per dissipation area in all designs

Comparative illustration of copper and CNT designs at 1000 rpm

Copper coils

CNT material coils (best conductivity)

with 1.1 times larger diameterand 0.75 times current density

CNT material coils (worst conductivity)

with 1.46 times larger diameterand 0.3 times current density

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Comparative Performance of AFPM with Cu and CNT Windings

• Parametric study 1 - number of stacks

• Parametric study 2 - stator axial length

• Parametric study 3 – outer diameter

• CNT #1 has the worst conductivity

• CNT #2 has the best conductivity.

CopperParametric 1 Parametric 2 Parametric 3

CNT #1 CNT #2 CNT #1 CNT #2 CNT #1 CNT #2

Active axial length [mm] 59 178 110 199.4 103.5 59 59

Active outer diameter [mm] 290 290 290 290 290 481.4 371.2

Number of turns 80 28 58 81 79 71 66

PM mass [kg] 1.54 5.14 3.08 6.35 3.07 4.89 2.74

Steel mass [kg] 0.79 0.79 0.79 0.79 0.79 2.18 1.29

Coil mass [kg] 7.20 4.02 2.41 4.97 2.40 3.32 1.98

Total active mass [kg] 9.54 9.95 6.28 12.12 6.26 10.40 6.01

Total volume [m3] 0.0057 0.0171 0.0106 0.0192 0.0100 0.0157 0.0093

Specific torque [Nm/kg] 2.09 2.01 3.18 1.65 3.19 1.92 3.33

Specific torque [Nm/m3] 3508.77 1169.59 1886.79 1041.67 2000.00 1273.88 2150.54

All machines are designed for the same rated torque (30 Nm) at the same speed (1000 rpm).

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Example Design Studies

Performance improvement achieved by replacing copper coils with carbon nanotube (CNT) windings. Machines with CNT windings maybe larger in size and lighter. AC supplementary losses in NCT windings are negligible. Further improvements possible due to better heath transfer.

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Parametric study 1 (stacks) Parametric study 2 (length) Parametric study 3 (diameter)

High Speed Operation

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Conclusion

• On going developments for carbon nano-tubes (CNT) with improved electric conductivity

• New materials may call for new design concepts – a synergetic multi-disciplinary approach is recommended

• Even with short term expected CNT improvements

• the material may have an advantage in terms of specific power per weight and high speed operation for specific topologies

• Illustrated on the proposed benchmark coreless axial flux PM machine

• The new CNT materials and related technologies may be disruptive

• It may take some time to deploy the new technology in conventional industrial applications

• First in line to benefit may be high-tech applications, such as those for aerospace, or high frequency electronics.

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References

[1] A. Lekawa-Raus, J. Patmore, L. Kurzepa, J. Bulmer, and K. Koziol, “Electrical properties of carbon nanotube based fibers and their future use in electrical wiring,” Advanced Functional Materials, vol. 24, no. 24, pp. 3661–3682, 2014.

[2] A. Lekawa-Raus, L. Kurzepa, X. Peng, and K. Koziol, “Towards the development of carbon nanotube based wires,” Carbon, vol. 68, pp. 597–609, 2014.

[3] L. Kurzepa, A. Lekawa-Raus, J. Patmore, and K. Koziol, “Replacing copper wires with carbon nanotube wires in electrical transformers,” Advanced Functional Materials, vol. 24, pp. 619–624, 2014.

[4] P. Juha, M. Juho, L. Pia, V. Julia, and O. Marcin, “At the cusp of the next electric motor revolution: Replacing copper with carbon nanomaterials,” in International Conference on Energy Efficiency in Motor Driven Systems, 2015.

[5] Frulla, G. 2002. Preliminary reliability design of a solar-powered high-altitude very long endurance unmanned air vehicle. Proceedings of the Institution of Mechanical Engineers 216, (4): 189, http://ezproxy.uky.edu/login?url=http:

[6] R. Hill-Cottingham, P. Coles, J. Eastham, F. Profumo, A. Tenconi, and G. Gianolio, “Multi-disc axial flux stratospheric aircraft propeller drive,” IEEE Industry Applications Conference, vol. 3, pp. 1634–1639, 2001.

[7] C. Subramaniam, T. Yamada, K. Kobashi, A. Sekiguchi, D. N. Futaba, M. Yumura, and K. Hata, “One hundred fold increase in current carrying capacity in a carbon nanotube-copper composite,” Nature communications, vol. 4, 2013

[8] Vandana Rallabandi, Narges Taran, D. M. Ionel and J. F. Eastham, “On the Feasibility of Carbon Nanotube Windings for Electrical Machines: Case Study for a Coreless Axial Flux Motor”, IEEE ECCE, Milwaukee WI, 2016.

[9] Vandana Rallabandi, Narges Taran, D. M. Ionel, and J. F. Eastham, “Coreless Multidisc Axial Flux PM Machine with Carbon Nanotube Windings”, accepted for publication in IEEE CEFC 2016, Nov 2016.

[10] Vandana Rallabandi, Narges Taran, and D. M. Ionel, “Multilayer Concentrated Windings for Axial Flux PM Machines”, accepted for publication in IEEE CEFC 2016, Nov 2016.

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University of Kentucky – Solar Car

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From Solar Airplanes to Carbon Nanotubes and Wires ... Nanotubes and Wires – Opportunities for the Coil Winding and Electric Machine Industries? Dan M. Ionel, Ph.D., IEEE Fellow