Coupled Electromagnetic and Thermal Solution For Electric Machine Design

 

C o up upll ed E l ec tro troma magg net netic ic and an d T her mal olution ution for fo r herm al S ol E l e c t r i c M ac a c h i ne ne D e s i g n

Xiao HU Zed Ze d (Zhangjun (Zhangj un)) TANG TANG  A NSYS, INC.  ANSYS,

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Introduction • Electric ma m achine chi ne desig design n is a multimulti -physic phy sics s problem pro blem  –   –   –   – 

Electromagnetic Fluid and thermal Mechanical (Stress, Vibration) Power electronics/control

• Electrom lectr oma agne gn eti tic, c, thermal and and mechanical designs desig ns are interrelated  –  Losses from electromagnetic design affect temperature  –  Temperature rise will change material properties  –  Thermal induced mechanical stress

•  A d esi es i g n env en v i r o n m ent en t t h at acc ac c o m m o d ates at es all al l p h y s i c s and the th eir inte in tera racti ction on is highly hig hly de d esire sir ed environment  –   ANSYS Workbench environment © 2009 ANSY ANSYS, S, In Inc. c. All right rights s rese reserved. rved.

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 S imulation D riven P roduct D evelopment -

E l e c t r i c M a c h i ne n e D e s i g n M e t ho h o d o lo g y  

Much better better solu tion with  ANSYS CFD/Mech CFD/Mec h an anic ic al

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 M a x w e l l2 D f o r E l e c t r o m a g n e t i c  • Majo jori rity ty of Electr lectrom oma agn gne eti tic c De Desi sign gns s are Don one e in 2D for fo r Elect Electri ric c Ma Mach chin ine e  –  >80%  –  Faster   –  Enough accuracy

• Maxwell2D Transient Solver   –  Transient excitation  –  Transient motion  –  Motion induced transient effects

oupl plin ing g betw betwe een Maxw xwe ell ll3 3D a and nd ANS ANSY YS is • Cou possi pos sible ble and ffoll ollows ows the sa same me de desi sign gn flow fl ow © 2009 ANSY ANSYS, S, In Inc. c. All right rights s rese reserved. rved.

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D e s i g n F lo low  

Centroids

Temperature

Workbench Mesher 

Geometry Workbench DM Maxwell UDP

Losses Maxwell

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Mapped Losses  ANSYS Mechanical (automated)  ANSYS CFD (Scripted)  ANSYS, Inc. Proprietary Proprietary

 

 A c c u r a t e L o s s C o u p li n g • Most Los Losse ses s are D Dist istrib ributed uted

 –  Eddy loss (PMs)

– Core loss (Stator & Rotor)

• Time im e Av Ave erage raged d Spa Spati tia al L Los osses ses  –  Time constants are very different for electrical and thermal © 2009 ANSY ANSYS, S, In Inc. c. All right rights s rese reserved. rved.

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E x p o rt T herma hermall Data to  A N S Y S M e c h a n i c a l

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I mp mpo o rt Max w el elll L o a d s to  A N S Y S M e c h a n i c a l

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 M a x w e l l 2 D – A N S Y S T h e r m a l

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 M e c h a n i c a l E i g e n m o d e a n a l y s i s o f thermal p rere-ss tres s ed mo mod d el w ith  M a x w e l l 3 D t r a n s i e n t lo loss s e s

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1 . 7 5 K H z m od o d e r e s u lt s o f    prr e -s t r e s s e d s t r u c t u r a l m o d e l  p

Thermal The rmal deformation deformatio n

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N ee d fo forr C omp omputa utati ti on onal al F luid D y na n a m ic ic s (CF D) • CFD is tthe he sc scie ience nce of predicti predicting ng fflui luid d fl flow ow and he hea at transfe transferr by sol solvin ving g ma mathema thematic tica al equations • Ele lectri ctric c machine cool cooling ing iinvolv nvolve es fl fluid uid flow f low and he hea at transfer a and nd thu thus sc ca an b be ene nefit fit from fro m CFD sim simul ula ation ti on

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C F D M o d e ls ls f o r E le c t r i c M ac ac hi n e • Con onju jugate gate hea heatt tr tra ans nsfer fer wit with h mappe mapped d lo loss sse es from fr om Maxw xwe ell  –  Solids with different properties

 –  Liquid or air for cooling  Air trapped inside electric machine  –  Air • Mult Multii pl ple eR Re eferenc ference eF Frame rame ((M MRF) us use ed t o accou ccount nt for roto rotorr rota rotation tion  –  Steady state solution with the impact of rotating rotor 

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C o o l i ng M et ho h o d s f or o r E l ec t ri c  M a c h i n e s • Forced orced conve conv ection liquid cooling coolin g

 –  Most effective cooling  –  Expensive • Force orc ed conve conv ection cti on air air coolin coo ling g

 –  Effective cooling  –  Somewhat expensive • Natura tur al convection co nvection air coolin coo ling g

 –  Not as effective  –  Cheap

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T e s t C a s e s a n d P u r po pos e s • Three test cases are conducted to see the effectiveness of cooling and different temperature and its gradient distribution

Cooling Cooli ng Me Meth thod od

Mesh Me sh Siz Size e (K)

Case 1

Forced Water

916

Case 2

Forced Air

1007

Case 3

Natural Air

899

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G eo eometry/ metry/Mes Mes h •  A s ec ectt o r o f g eo eom m et etrr y i s u s ed

 –  Periodic boundary • Hex is us use ed in mo most st of the regio regions ns

 –  Except for the winding and the fluid region surrounding it, etc. • Forc orce ed a air ir co cooli oling ng has a an na air ir domain do main outside outsi de

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L o s s Di s t ri but b utii on o n f o r A l l C a s es • Spatial eddy loss distribution for the magnets • Spatial core loss distribution for the rotor, stator yoke, and stator teeth • Stranded winding copper loss •  All losses, which are highly non-uniform, non-uniform, are from Maxwell2D

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T emp emperat erature ure Di s tribu tributio tion n • Max temperature are 398K, 517K, and 550k respectively • Forced water cooling is the most effective and natural air cooling is the least. • Forced water cooling gives similar max temperature gradient • Temperature gradient is responsible for thermal stress. • To keep both temperature and its gradient low is the best

Forced water cooling © 2009 ANSY ANSYS, S, In Inc. c. All right rights s rese reserved. rved.

Forced air cooling 18

Natural air cooling  ANSYS, Inc. Proprietary Proprietary

 

 S u m m a r y f o r F o r c e d C o o l i n g • Force orc ed wate waterr c cool ooling ing is the most effectiv ffective e. • Natu tural ral a air ir c coo ooli ling ng iis s tthe he lea least st eff ffe ectiv ct ive e. • Forced or ced wa water ter coo cooli ling ng,, ho howeve wever, r, do doe es no nott necess nece ssa ari rily ly gi give ve the le lea ast tempe temperatur rature e gradient. tural ral a air ir c coo ooli ling ng m ma ay ffa ace ch cha all lle eng nge e of hig h igh h • Natu temperature. or ced wa water ter coo cooli ling ng m ma ay ffa ace ch cha all lle eng nge e of • Forced high hi gh tte emp mpe eratur rature e gr gra adi die ent nt..

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Ob s er vat Obs vations ions a b o ut N a tural C o nvec tion C o o l ing • Natu Natural ral co conv nvectio ection n He Heat at T Transf ransfer er C Coeffi oeffici cie ent (HT (HTC) is relatively uniform unifor m compare compared d with fo forced rced conve convection ction • Natural convection cooling can be simulated by using a constant HTC instead of a full CFD calculation. • Well accepted industry practice. •  A  Aii r t r ap app p ed i n s i d e el elec ectt r i c m ac ach h i n es i s n o t ef efff ec ectt i v e iin n h eat transfer and and th thus us can be removed from tthe he calcu calculation. lation. •  Air gap kept but modeled by STILL STILL air (details next) • If air domains bo both th insid in side e and ou outsid tside e of th the e electric m ma achi chine ne are remov remove ed, the pro problem blem be becom come es pur pure ely condu co nducti ctive ve • No full CFD

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I ne neff f ec t i v enes en es s o f T ra rap p p ed A i r  • Relatively low velocity and uniform temperature of the trapped air explains its ineffectiveness for heat transfer 

Velocity vector of trapped air (note the max velocity is only 2.5 m/s) © 2009 ANSY ANSYS, S, In Inc. c. All right rights s rese reserved. rved.

Temperature distribution of trapped air (note the temperature scale goes from 500K to 530K) 21

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T e s t C a s e s U s i ng n g N a t u r al al C o nv nvec ec tio tion n A ir C o o ling • Case 3 is from previous study and is used as a based line case here. • Case 4 contains only solids • Case 5 also contains the air gap between the rotor and stator to improve the accuracy. • The air gap is treated as if it is solid

Cooling Method

Trapped  Aii r   A

Full CFD

 Aii r Gap  A

Mes h Mesh Size (K)

Case 3

Natural

Yes

Yes

Yes

899

Case 4

 Air  Natural  Air 

No

No

No

394

Case 5

Natural

No

No

Yes

397

 Air  © 2009 ANSY ANSYS, S, In Inc. c. All right rights s rese reserved. rved.

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T emp emperat erature ure Di s tribu tributio tion n • Max temperatures are 550K, 566K, and 563k respectively • Trapped air has minimum impact on max temperature as expected •  Air gap has an impact on rotor temperature distribution

Full CFD (case3) © 2009 ANSY ANSYS, S, In Inc. c. All right rights s rese reserved. rved.

Solid on only, n no o CF CFD (c (case4) 23

 Air gap

Solid an and ai air g ga ap, n no o CF CFD (c (case5)  ANSYS, Inc. Proprietary Proprietary

 

Comparison

Max Windi ng Max Temp Te mperature erature (K)

Er r o r

Max Ro t o r Temp Te mperature erature (K)

Error 

Performance on 4 CPUs CPUs

Case 3 Case 4

550 566

0% 2.9%

528 508

0% 3.8%

4 ~ 12 hrs