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A Permanent Magnet Traction Motor for Electric Forklifts: Design and Iron Loss Analysis with Experimental Verifications
KTH, School of Electrical Engineering (EES), Electrical Machines and Power Electronics.
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

This thesis presents the design analysis of a permanent magnet synchronous motor (PMSM) for the traction application in electric forklifts. Within the scope of the study, an existing induction traction motor for electric forklifts benchmarks the expected performances of the proposed PMSM designs, as design specifications. The possibility of using the same stator geometry as the one used in the induction motor is explored for fast prototyping. The eventual prototype design is expected to be field-weakened and to have a constant power speed range (CPSR) of 2.5 to 3.

A simple analytical design approach based on the CPSR contour plot in an interior permanent magnet parameter plane is derived to obtain the possible designs that meet all the design specifications and the targeted CPSR. A prototype design with an inset permanent magnet (IPM) rotor configuration is obtained with this approach. Finite Element Method (FEM) analysis is employed to verify the expected performance. In addition, further examinations are also carried out by taking into consideration the magnetic saturation and the stator resistance. Contour plots of torque and phase voltage are applied to procure the advanced current angle required at different speeds in the field-weakening operating region.

Two prototype motors have been manufactured during this thesis work, and various experimental tests are carried out to examine and validate the expected performance. The prototype can deliver a maximum output power of 9.4 kW at the rated speed of 1500 rpm, and it has an outer diameter of 180 mm, a shaft height of 112 mm, a bore diameter of 110 mm and an active length of 165 mm. Search coil windings are implemented in the main prototype to monitor and measure the flux density waveforms in the stator tooth and the yoke back. The prototypes are naturally cooled with the cooling fins and the ventilation holes in the stator housing. The thermal analysis based on the lumped-circuit approach and the numerical method are investigated and examined by the measured results. It has been shown that an accurate loss estimation is a pre-requisite to enable both approaches to accurately analyze the heat transfer phenomenon in electric machines. The strengths and disadvantages of each method are also discussed.

An analytical approach to estimate the iron loss in permanent magnet (PM) electrical machines is also developed and extensively investigated. The proposed technique is based on the flux density waveforms predicted in the various parts of the stator, namely the tooth, tooth projection and the yoke back. The waveform in the respective region is derived from the air gap flux density that consists of a fixed PM excitation and the armature field due to the fundamental current in the stator winding. The model can be applied at any operating point with different load, including the field-weakening region. This simple approach gives a good indication on how iron loss varies at various speeds and operating points. The predicted loss shows a very satisfactory agreement (± 4%) with the measured results at no-load or open-circuit condition, but larger discrepancies are found under the load condition. In the constant torque operation region, estimated losses are approximately on average 15% lower than the measured values. Under the field-weakening operation, the model becomes inadequate due to the excess eddy current loss caused by the highly distorted tooth flux density waveform. A correction factor for the eddy current loss is therefore essential to account the harmonic effect. The rectified estimations are then within ± 21% of the measured values. This simple approach has proved to be capable of estimating and modelling the difficult phenomenon of iron loss in PM motors, and it can be easily embedded in the design process for routine use in loss estimations.

Keywords: Constant Power Speed Range, Electric Forklift, Finite Element Analysis, Field-weakening Capability, Iron Loss, Permanent Magnet Electrical Motor, Saliency, Thermal Analysis

Place, publisher, year, edition, pages
Stockholm: KTH , 2006. , ix, 232 p.
Series
Trita-EE, ISSN 1653-5146 ; 2006:59
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-4241ISBN: 978-91-7178-520-6 (print)OAI: oai:DiVA.org:kth-4241DiVA: diva2:11419
Public defence
2006-12-19, M3, KTH, Brinellvägen 64, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100903Available from: 2006-11-15 Created: 2006-11-15 Last updated: 2010-09-03Bibliographically approved
List of papers
1. Thermal analysis - Lumped-circuit model and finite element analysis
Open this publication in new window or tab >>Thermal analysis - Lumped-circuit model and finite element analysis
2003 (English)In: IPEC 2003: Proceedings of the 6th International Power Engineering Conference, SINGAPORE: NANYANG TECHNOLOGICAL UNIV , 2003, 952-957 p.Conference paper, Published paper (Other academic)
Abstract [en]

This paper presents the thermal analysis of Permanent Magnet Synchronous Motors (PMSMs) for electric vehicle traction applications. Modem thermal design techniques can be classified into two general methods, analytical lumped circuit and numerical analysis. It is the aim of this paper to investigate the strengths and weaknesses of the two approaches. Two commercially available thermal design packages, Motor-CAD and FEMLAB, are used in our investigation. Motor-CAD is a 3-dimensional (3-D) lumped circuit analysis package dedicated to the thermal design of motors. FEMLAB is a multi-physics 2- and 3-dimensional finite element analysis (FEA) package.

Place, publisher, year, edition, pages
SINGAPORE: NANYANG TECHNOLOGICAL UNIV, 2003
Keyword
thermal, Permanent Magnet Synchronous Motors, lumped-circuit, finite element method (FEM)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24307 (URN)000234294200168 ()
Conference
IPEC 2003: 6th International Power Engineering Conference
Note
QC 20100901Available from: 2010-09-01 Created: 2010-09-01 Last updated: 2010-09-03Bibliographically approved
2. Modeling of iron losses in permanent magnet synchronous motors with field-weakening capability for electric vehicles
Open this publication in new window or tab >>Modeling of iron losses in permanent magnet synchronous motors with field-weakening capability for electric vehicles
2003 (English)In: International Journal of Automotive Technology, ISSN 1229-9138, E-ISSN 1976-3832, Vol. 4, no 2, 87-94 p.Article in journal (Refereed) Published
Abstract [en]

Recent advancements of permanent magnet (PM) materials and solid-state devices have contributed to a substantial performance improvement of permanent magnet machines. Owing to the rare-earth PMs, these motors have higher efficiency, power factor, output power per mass and volume, and better dynamic performance than induction motors without sacrificing reliability. Not surprisingly, they are continuously receiving serious considerations for a variety of automotive and propulsion applications. An electric vehicle (EV) requires a high-efficient propulsion system having a wide operating range and A capability of generating a high peak torque for short durations. ne improvement of torque-speed performance for these systems is consequently very important, and researches in various aspects are therefore being actively pursued. A great emphasis has been placed on the efficiency and optimal utilization of PM machines. This requires attention to many aspects related to the machine design and overall performance. In this respect, the prediction of iron losses is particularly indispensable and challenging, especially for drives with a deep field-weakening range. The objective of this paper is to present iron loss estimations of a PM motor over a wide speed range. As aforementioned, in EV applications core losses can be significant during high-speed operation and it is imperative to evaluate these losses accurately and take them into consideration during the motor design stage. In this investigation, the losses are predicted by using an analytical model and a 2D time-stepped finite element method (FEM). The results from different analytical approaches are compared with the FEM computations. The validity of each model is then evaluated by these comparisons.

Keyword
efficiency, electric drive, EV, modeling, permanent magnet motor, power density, core losses
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-22744 (URN)000184699200004 ()
Note
QC 20100901Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-09-03Bibliographically approved
3. A theoretical study on permanent magnet synchronous motors for electric vehicles
Open this publication in new window or tab >>A theoretical study on permanent magnet synchronous motors for electric vehicles
2003 (English)In: IPEC 2003: PROCEEDINGS OF THE 6TH INTERNATIONAL POWER ENGINEERING CONFERENCE, SINGAPORE: NANYANG TECHNOLOGICAL UNIV , 2003, 435-440 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper addresses the theoretical design of a conventional radial flux permanent magnet synchronous motor (PMSM) with field-weakening capability for electric vehicles. The study applies to both surface mounted and inset magnet rotor configurations. Various losses estimations are embedded into the design procedures to ensure that the desired overall drive performance is achieved. Influences of parameters such as air gap size and magnet thickness on the performances are studied. Back EMF and cogging torque are also investigated and analysed by using both the Finite Element Method (FEM) and an analytical approach. Design examples of various PMSMs with a given stator geometry are presented.

Place, publisher, year, edition, pages
SINGAPORE: NANYANG TECHNOLOGICAL UNIV, 2003
Keyword
permanent magnet synchornous motors (PMSMs), field-weakening, electric vehicles (EVs)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24306 (URN)000234294200077 ()
Conference
IPEC 2003: 6TH INTERNATIONAL POWER ENGINEERING CONFERENCE
Note
QC 20100901Available from: 2010-09-01 Created: 2010-09-01 Last updated: 2010-09-03Bibliographically approved
4. Design study of a traction motor for electric vehicles
Open this publication in new window or tab >>Design study of a traction motor for electric vehicles
2005 (English)In: ICEMS 2005: Proceedings of the Eighth International Conference on Electrical Machines and Systems, 2005, Vol. 1, 786-791 p.Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents the design study of a traction motor used in electric vehicles. The design is a permanent magnet synchronous motor (PMSM) type with an inset permanent rotor configuration. With the given constant power speed range (CPSR), a design methodology is developed to reach the required specifications.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24343 (URN)000235646000172 ()2-s2.0-33846975135 (Scopus ID)978-750627407-4 (ISBN)
Conference
Eighth International Conference on Electrical Machines and Systems
Note
QC 20100902Available from: 2010-09-02 Created: 2010-09-02 Last updated: 2011-07-13Bibliographically approved
5. A permanent magnet synchronous motor for traction applications of electric vehicles
Open this publication in new window or tab >>A permanent magnet synchronous motor for traction applications of electric vehicles
2003 (English)In: IEEE IEMDC'03: IEEE INTERNATIONAL ELECTRIC MACHINES AND DRIVES CONFERENCE, VOLS 1-3, NEW YORK: IEEE , 2003, 1035-1041 p.Conference paper, Published paper (Other academic)
Abstract [en]

This paper presents the design of a Permanent Magnet Synchronous Motor (PMSM) for traction applications of electric vehicles (EVs). The design is based on the stator geometry of an existing commercial available induction traction motor. The rotor configurations considered in this study are the surface mounted. magnet (SPM) and the inset permanent magnet (IPM) types. Both designs are investigated for the identical specification and their overall performances are-compared with the existing asynchronous motors. A schematic block diagram of the design flow chart applied is Illustrated. An analytical approach for calculating stator iron loss [1] is applied in the design procedure to ensure the required performance is reached. A thermal analysis of the prototype motor based on the lumped-circuit model and finite element analysis is also presented. Lastly, conclusions on the overall performance of. PMSMs for electric vehicle applications are made and discussed.

Place, publisher, year, edition, pages
NEW YORK: IEEE, 2003
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24344 (URN)000183794800153 ()
Conference
IEEE INTERNATIONAL ELECTRIC MACHINES AND DRIVES CONFERENCE
Note
QC 20100902Available from: 2010-09-02 Created: 2010-09-02 Last updated: 2010-09-03Bibliographically approved
6. transient thermal analysis using both lumped-circuit and finite element method of a permanent magnet traction motor
Open this publication in new window or tab >>transient thermal analysis using both lumped-circuit and finite element method of a permanent magnet traction motor
2006 (English)In: Transactions of south african institute of electrical engineers, 2006Conference paper, Published paper (Refereed)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-24340 (URN)
Note
QC 20100902Available from: 2010-09-02 Created: 2010-09-02 Last updated: 2010-09-03Bibliographically approved

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