Performance and Cost Assessment for Motors Using Alternative Rare Earth Free Magnets. Dr. Peter Campbell, Consultant

Transcription

1 Performance and Cost Assessment for Motors Using Alternative Rare Earth Free Magnets Dr. Peter Campbell, Consultant Acknowledgement: Author is a consultant to Northeastern University on a project funded under a cooperative agreement with U.S. Department of Energy's Advanced Research Project Agency Energy (ARPA E)

2 Critical Materials in Clean Energy DOE s ARPA-E is funding 14 projects in its Rare Earth Alternatives in Critical Technologies ( REACT ) program, aimed at developing costeffective alternatives to rare earths used for clean energy applications: 1 U.S. Department of Energy:

3 Critical Materials in Clean Energy Clean energy applications such as wind turbines and electric vehicles utilize magnets containing rare earth elements: 2 U.S. Department of Energy: Critical Materials Strategy, Dec. 2011

4 Rare Earth Element Criticality Rare earth magnets are of high importance to electric vehicle motors and wind generators, and their constituents Neodymium and Dysprosium are subject to continued high supply risk: Short term (0 5 years) Medium term (5 15 years) 2 U.S. Department of Energy: Critical Materials Strategy, Dec. 2011

5 Rare Earth Demand Percentage of total Demand for Neodymium oxide in 2010 was 29,243 tons, derived from USITC data for all types of metal permanent magnets imported to the U.S. 3 Arnold Magnetic Technologies: Materials & Magnet Market Update; SMMA Spring 2012 Management Conference.

6 Projected Rare Earth Demand Projected Demand for Neodymium oxide in 2015: 45,037 tons Percentage of total 3 Arnold Magnetic Technologies: Materials & Magnet Market Update; SMMA Spring 2012 Management Conference.

7 Rare Earth Supply Risk Critical applications require magnets to operate up to 180 o C Demand for dysprosium oxide in 2010: 2,843 tons (also derived from USITC data for metal permanent magnets imported to the U.S.) Projected demand for dysprosium oxide in 2015: 5,115 tons Meeting the demand depends upon Chinese raw material: Ionic clay, Jianzxi, China Bastnaesite, Mt. Pass, U.S.A.

8 Projected Rare Earth Supply 2 U.S. Department of Energy: Critical Materials Strategy, Dec. 2011

9 Rare Earth Supply Shortage Worldwide 2010 rare earth oxide production figures 2 do not even cover the estimated demand for use in U.S. metal magnets, as derived from USITC import data 3 ; Regardless of this discrepancy, by 2015 there will be shortfalls in the supply rare earths for critical applications, most serious for dysprosium, but also for neodymium; Such rare earth shortage would no doubt impact the projected growth of clean energy applications, particularly the already popular use in electric vehicle drive motors.

10 Rare Earth-Free Magnet Research One of DOE s ARPA-E projects under its Rare Earth Alternatives in Critical Technologies ( REACT ) program is a collaboration between university and industrial research groups, led by Northeastern University: Multiscale Development of L1 0 Materials for Rare-Earth-Free Permanent Magnets

11 Rare Earth-Free Magnet Research Goal: Create a magnet with zero rare earth content bridging the magnetic property void between ferrite and sintered rare earth-based magnets: Target energy product, (BH) max > 12 MGOe at 180ºC. Of the various sources of magnetic anisotropy, magnetocrystalline anisotropy provides the largest anisotropy and is predominant in today s high energy permanent magnets. Successful development of a high energy rare earth-free magnet requires an alternative source to the magnetocrystalline anisotropy arising from the 4f electronic state. 4 L.H. Lewis, K. Barmak, J.G. Goldstein, F. Pinkerton and R. Skomski: Towards Stabilization of L1 o - type FeNi Compounds for Permanent Magnet Applications, 22 nd International Workshop on Rare Earth Magnets and Their Applications (REPM 12), Nagasaki, September J. Paulevé, A. Chamberod, K. Krebs and A. Bourette: Magnetization Curves of Fe-Ni (50-50) Single Crystals Ordered by Neutron Irradiation with an Applied Magnetic Field, J. Appl. Phys., vol.39 (2) p.989, Feb

12 Rare Earth-Free Magnet Research A select group of transition-metal compounds form in the tetragonal L1 o structure with strong uniaxial magnetic anisotropy aligned perpendicular to the basal plane. One member of this group is L1 o -type FeNi (naturally occurring in certain meteorites and known as tetranite). Disordered FCC L1 0 -type structure with magnetic anisotropy Composition M S (kg) H A (koe) T C ( o C) Nd 2 Fe 14 B L1 o FeNi M s (saturation magnetization) is the maximum induced magnetic moment that can be obtained in a magnetic field (relates to B r ) ; H A, (magnetocrystalline anisotropy) is the energy necessary to deflect the magnetic moment in a single crystal from the easy to the hard direction (relates to H ci ).

13 Case Study: EV Drive Motor This case study is based on the design of a drive for a midsized hybrid EV sedan, whose typical motor would produce a peak power of 55kW for 18sec. from 2,000 to 10,000 rev/min. 6 U.S. Department of Energy report IS-5191: System Cost Analysis for an Interior Permanent Magnet Motor. 7 U.S. Department of Energy report ORNL/TM-2006/UQM: FreedomCAR Advanced Traction Drive Motor Development. 8 U.S. Department of Energy report ORNL/TM-2010/253: Evaluation of the 2010 Toyota Prius Hybrid Synergy Drive System.

14 EV Drive Motor Targets Targets for motor s active materials (stator & rotor cores, winding, magnets) are 20kg (.36 kg/kw) & $175 ($3.2/kW); Electric propulsion system should be able to operate on input voltages from fuel cells or batteries that range from 200 to 450V; To limit the sizes of wiring & semiconductors, maximum motor phase current is 400A; torque (Nm) speed (r.p.m.) Peak power must be developed at the minimum 200V supply and at 400A phase current; Efficiency should be >93% from 1,000 to 10,000 rev/min. at 20% of rated torque (i.e. at 262 x 0.2 = 52 Nm);

15 EV Drive Motor with IPM Rotor The motor topology has an internal permanent magnet (IPM) rotor, a cross between a traditional p.m. motor and a reluctance motor. IPM meets back-e.m.f. and minimum voltage constraints more easily than SPM. Re-designed to optimize use of its sintered Nd-Fe-B magnets: (inches) Stator diameter: 8.70 Rotor diameter: 6.04 Stack length: 3.40 Air gap: Magnet thickness: 0.100

16 EV Drive Motor with SPM Rotor An alternative motor topology satisfying the same specification uses a surface-mount permanent magnet (SPM) rotor, also designed to optimize use of its sintered Nd-Fe-B magnets. Eddy-current losses in magnets heating. Surface mount magnets require retention larger air gap, l g. Overall stator and rotor dimensions unchanged.

17 Motor Modeling The hybrid function of the IPM design is characterized using d-, q-axis analysis (r.m.s. values); Ψ m, d- and q-axis inductances calculated using FEA; T = 3p {Ψ m I q (L q L d )I d I q } i.e.: alignment + reluctance torque In IPM: L q >L d (I d normally ve); In SPM: L q L d, so: T = 3pΨ m I q = (3p/ω)E q I q

18 Sintered Nd-Fe-B Magnet Grade Under extreme steady state conditions, the magnet must operate up to 180 o C, so the motors were designed using ND35UH grade magnets:

19 Rotor Demagnetization Under extreme steady state conditions and peak phase current (400A), worst case demagnetization of the ND35UH magnets at 180 o C was analyzed using finite element analysis to ensure there is no irreversible loss of magnetization:

20 Peak Power at Minimum Voltage Motor with IPM rotor achieves its required 55kW peak operating profile (while meeting target active material weight) with contribution from both alignment torque and reluctance torque over the full speed range:

21 Rare Earth-Free Magnet s Target Optimization using FEA yields a minimum spec. for the new magnet s demagnetization characteristic to retain overall motor dimensions: At 180 o C, (BH) max 16 MGOe J, B (G) H (Oe)

22 Rotor Demagnetization Replacing sintered N35UH with the anticipated new rare earth-free magnets, the inevitably lower H ci is compensated with thicker magnets (greater l m ) in both the IPM and the SMP rotor topologies. Gain in magnet volume with rare earth-free: +88% (IPM) and +80% (SPM); Demagnetization at 180 o C is again analyzed to check no irreversible loss of magnetization:

23 Peak Power at Minimum Voltage Motor with IPM rotor achieves its required 55kW peak operating profile (while meeting target active material weight) with contribution from both alignment torque and reluctance torque over the full speed range:

24 Benefit vs. Sintered Nd-Fe-B For this EV drive motor utilizing N35UH grade sintered Nd-Fe-B, raw material value is saved by adopting rare earth-free magnets: N35UH GRADE ALLOY Nd Pr Dy Fe Co B Composition, wt%: Price 8, $/kg (FOB China): EV DRIVE MOTOR Magnet weight/motor + ALLOY & MAGNET PROCESS YIELD 10 Rare earth price/motor With IPM rotor: 650 gm. $69 With SPM rotor: 670 gm. $71 Target active material cost $175 9 as of December, 2012: Metal Pages Ltd, 10 private communication: Steve Constantinides, Arnold Magnetic Technologies, Sept. 2012

25 Dysprosium Price Fluctuations Current price (FOB China)

26 Neodymium Price Fluctuations Current price (FOB China) 9 Metal Pages Ltd,

27 The Rare Earth-Free Magnet Research Goal: Create a magnet with zero rare earth content bridging the magnetic property void between ferrite and sintered rare earth-based magnets: Target energy product, (BH) max > 12 MGOe at 180ºC. EV drive motor requirement: the new magnet should achieve: B r 8.1 kg; H ci -5.7 koe; H c -4.9 koe at 180 o C (BH) max 16 MGOe at 180 o C, ( 24 MGOe at 20 o C) Motors, industrial, general, auto etc. the largest segment of the current rare earth magnet market, with significant potential growth enabled by replacing ceramic ferrite with this rare earth-free magnet in applications such as automotive accessory motors to reduce vehicle weight.

28 Conclusions The benefits of replacing rare earth magnets with the anticipated rare earth-free magnet include: Providing freedom from future unpredictable rare earth pricing fluctuations and supply risks; Providing savings of all rare earth raw material cost; Not necessarily having a negative impact the size, weight, or performance of a motor; Feasibility being readily determined and demonstrated by product re-design of any motor using FEA. We would like to engage potential users ongoing involvement in evaluating rare earth-free material specifications and new magnet materials: Contact: Dr. Peter Campbell: drpeterc@earthlink.net; (919)