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Thermal Analysis and Management of High-Performance Electrical Machines
KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis deals with thermal management aspects of electric machinery used in high-performance  applications  with  particular  focus put  on electric machines designed for hybrid electric vehicle applications.

In the first part of this thesis,  new thermal models of liquid (water and oil) cooled electric machines are proposed.  The proposed thermal models are based on a combination of lumped parameter (LP)  and numerical methods. As  a first  case study,  a permanent-magnet  assisted  synchronous reluctance machine (PMaSRM) equipped with a housing water jacket is considered.  Particular focus is put on the stator winding and a thermal model is proposed that divides the stator slot into a number of elliptical copper and impregna- tion layers.  Additionally, an analysis, using results from a proposed simplified thermal finite element (FE)  model representing only a single slot of the sta- tor and its corresponding end winding, is presented in which the number of layers and the proper connection between the parts of the LP thermal model representing the end winding and the active part of winding are determined. The approach is attractive due to its simplicity  and the fact  that it closely models the actual temperature distribution for common slot geometries.  An oil-cooled induction machine where the oil is in direct contact with the stator laminations  is also considered.  Here, a multi-segment structure is proposed that  divides  the  stator,  winding and cooling  system  into  a number  of an- gular  segments.   Thereby,  the  circumferential  temperature  variation  due to the  nonuniform distribution  of the  coolant  in the  cooling  channels  can be predicted.

In the  second part  of this  thesis,  the  thermal  impact  of using  different winding impregnation  and steel  lamination  materials  is  studied.   Conven- tional varnish, epoxy and a silicone based thermally conductive impregnation material are investigated and the resulting temperature distributions in three small induction machines are compared. The thermal impact of using different steel lamination materials is investigated by simulations using the developed thermal  model  of the water  cooled  PMaSRM. The  differences  in alloy con- tents and steel lamination thickness are studied separately and a comparison between the produced iron losses and the resulting hot-spot temperatures is presented.

Finally, FE-based approaches  for  estimating  the  induced  magnet  eddycurrent losses in the rotor of the considered PMaSRM are reviewed and compared in the  form  of a case  study  based on simulations.   A  simplified three-dimensional  FE model  and an analytical  model,  both  combined  with time-domain 2D FE analysis, are shown to predict the induced eddy current losses with a relatively good accuracy compared to a complete 3D FE based model.  Hence, the two simplified approaches are promising which motivates a possible future experimental verification.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. , x, 83 p.
Series
Trita-EE, ISSN 1653-5146 ; 2013:022
Keyword [en]
Computational fluid dynamics, directly cooled electric machines, finite element analysis, heat transfer, hybrid electric vehicle, induction machines, lumped-parameter thermal model, permanent-magnet assisted synchronous reluctance machines.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-122695ISBN: 978-91-7501-733-4 (print)OAI: oai:DiVA.org:kth-122695DiVA: diva2:623376
Public defence
2013-06-13, sal F3, Lindstedtsvägen 26, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Note

QC 20130528

Available from: 2013-05-28 Created: 2013-05-27 Last updated: 2013-05-28Bibliographically approved
List of papers
1. Thermal Analysis of a PMaSRM Using Partial FEA and Lumped Parameter Modeling
Open this publication in new window or tab >>Thermal Analysis of a PMaSRM Using Partial FEA and Lumped Parameter Modeling
2012 (English)In: IEEE transactions on energy conversion, ISSN 0885-8969, E-ISSN 1558-0059, Vol. 27, no 2, 477-488 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an advanced lumped parameter (LP) thermal model for a permanent-magnet assisted synchronous reluctance machine (PMaSRM) developed for propulsion in a hybrid electric vehicle. Particular focus is put on the stator winding and a thermal model is proposed that divides the stator slot into a number of elliptical copper and impregnation layers. The model is enabled by the derivation of an approximate analytical expression for the thermal resistance of an elliptical cylinder with constant thickness. The approach is attractive due to its simplicity and the fact that it closely models the actual temperature distribution for common slot geometries. Additionally, an analysis, using results from a proposed simplified thermal finite element model representing only one slot of the stator and its corresponding end winding, is presented in which the number of layers and the proper connection between the parts of the LP thermal model representing the end winding and the active part of winding is determined. The presented thermal model is evaluated experimentally on a PMaSRM equipped with a water cooling jacket, and a good correspondence between the predicted and measured temperatures is obtained.

Keyword
Finite element analysis (FEA), hybrid electric vehicle (HEV), lumped parameter (LP) model, permanent-magnet assisted synchronous reluctance machines (PMaSRM), thermal measurements, thermal model
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Energy
Identifiers
urn:nbn:se:kth:diva-77525 (URN)10.1109/TEC.2012.2188295 (DOI)000304247200027 ()2-s2.0-84861454553 (Scopus ID)
Funder
StandUp
Note

QC 20150629

Available from: 2012-02-07 Created: 2012-02-07 Last updated: 2017-12-08Bibliographically approved
2. Thermal analysis of permanent-magnet synchronous reluctance machines
Open this publication in new window or tab >>Thermal analysis of permanent-magnet synchronous reluctance machines
2011 (English)In: 14th European Conference on Power Electronics and Applications, 2011Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a thermal analysis of permanent-magnet synchronous reluctance machines (PM-SRM). Particular focus is put on the rotor and two lumped parameter (LP) thermal models of the rotor are implemented and evaluated. The results of the two LP thermal models are compared to thermal simulations using the finite element method (FEM). Induced eddy current losses in the permanent magnets are computed using three-dimensional (3D) FEM computations whereas the losses in the electrical steel are obtained using a 2D FEM model. Based on type of cooling system, two cases are evaluated and the agreement between the two LP thermal simulations and the thermal FEM simulation is generally good but particular differences are highlighted. In the first case, the water cooling system manages to effectively handle the dominating copper losses which results in only a minor temperature difference between the shaft and the inner part of the stator teeth. In the second case, it is assumed that there is a significant temperature difference between the rotor shaft and the stator.

Keyword
Electric vehicle, Hybrid electric vehicle, Thermal design, Cooling
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-43249 (URN)000308003502011 ()2-s2.0-80053552004 (Scopus ID)978-161284167-0 (ISBN)
Conference
14th European Conference on Power Electronics and Applications, EPE 2011. Birmingham. 30 August 2011 - 1 September 2011
Funder
StandUp
Note

QC 20111116

Available from: 2011-10-13 Created: 2011-10-13 Last updated: 2014-09-11Bibliographically approved
3. Thermal Modeling of Directry Cooled Electric Machenes Using Lumped Parameter and Limited CFD Analysis
Open this publication in new window or tab >>Thermal Modeling of Directry Cooled Electric Machenes Using Lumped Parameter and Limited CFD Analysis
Show others...
(English)Article in journal (Other academic) Submitted
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-122839 (URN)
Note

QS 2013

Available from: 2013-05-28 Created: 2013-05-28 Last updated: 2013-09-12Bibliographically approved
4. Evaluation of Impregnation Materials for Thermal Management of Liquid-Cooled Electric Machines
Open this publication in new window or tab >>Evaluation of Impregnation Materials for Thermal Management of Liquid-Cooled Electric Machines
2014 (English)In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 61, no 11, 5956-5965 p.Article in journal (Refereed) Published
Abstract [en]

In this paper, the thermal impact of using different impregnation materials on high-performance liquid-cooled electric machines is studied. In this regard, varnish, Epoxylite, and a silicone-based thermally conductive material are considered. To study thermal effects of using different impregnation materials in theory, an advanced lumped-parameter thermal model of the studied electric machines is developed. In addition to the simulation studies, three identical induction machines using the aforementioned materials are manufactured and evaluated. Experimental tests are carried out at a wide range of current magnitudes and cooling conditions. A good agreement between the temperature measurements and corresponding simulation results is observed. It is demonstrated that using innovative thermally conductive materials in the stator slots and the end winding bodies of liquid-cooled electric machines results in a significant reduction in the winding hot spot temperature. Additionally, the influence of the critical parameters on the impregnation material performance, e. g., impregnation goodness and slot fill factor, is studied.

Keyword
Computational fluid dynamics, direct oil cooling, Epoxylite, hybrid electric vehicle (HEV), impregnation material, induction machines, lumped parameter (LP) thermal model, silicone-based thermally conductive material (SbTCM), vacuum impregnation, varnish
National Category
Control Engineering Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-122841 (URN)10.1109/TIE.2014.2308151 (DOI)000337123000016 ()2-s2.0-84902340101 (Scopus ID)
Funder
StandUpSwedish Energy Agency
Note

Updated from Submitted to Published. QC 20140715

Available from: 2013-05-28 Created: 2013-05-28 Last updated: 2017-12-06Bibliographically approved
5. Evaluation of stator and rotor lamination materials for thermal management of a PMaSRM
Open this publication in new window or tab >>Evaluation of stator and rotor lamination materials for thermal management of a PMaSRM
Show others...
2012 (English)In: Proceedings of the 20th International Conference on Electrical Machines, ICEM 2012, 2012, 1309-1314 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, the thermal impact of using different steel laminations in the stator and the rotor of a permanentmagnet assisted synchronous reluctance machine designed for an automotive application is studied. In this regard, two main parameters of the steel lamination materials, thickness and amount of alloy content in weight percent, are studied. Frequency characteristics of the iron losses of the studied materials are used to estimate iron losses in the stator and rotor laminations. An accurate lumped parameter model including a housing water jacket cooling system is used to model thermal effects and estimate the temperature distribution in critical parts of the machine. The predicted temperature distributions in the machines show that using lamination materials with different amounts of alloy content leads to 2%-10% variation in the temperatures of rotor and winding. However, using materials with different thicknesses results in substantial temperature changes in critical parts of the machine (up to 75%).

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - Transport
Identifiers
urn:nbn:se:kth:diva-104795 (URN)10.1109/ICElMach.2012.6350046 (DOI)000333806701044 ()2-s2.0-84870804197 (Scopus ID)978-146730142-8 (ISBN)
Conference
20th International Conference on Electrical Machines (ICEM12), Marseille 2-5 September 2012
Funder
StandUpTrenOp, Transport Research Environment with Novel Perspectives
Note

QC 20130111

Available from: 2012-11-13 Created: 2012-11-13 Last updated: 2014-10-14Bibliographically approved

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