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Modeling of iron losses in permanent magnet synchronous motors with field-weakening capability for electric vehicles
KTH, Superseded Departments, Electrical Systems.
KTH, Superseded Departments, Electrical Systems.ORCID iD: 0000-0002-8990-3745
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.

Place, publisher, year, edition, pages
2003. Vol. 4, no 2, 87-94 p.
Keyword [en]
efficiency, electric drive, EV, modeling, permanent magnet motor, power density, core losses
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
URN: urn:nbn:se:kth:diva-22744ISI: 000184699200004OAI: diva2:341442
QC 20100901Available from: 2010-08-10 Created: 2010-08-10 Last updated: 2010-09-03Bibliographically approved
In thesis
1. A Permanent Magnet Traction Motor for Electric Forklifts: Design and Iron Loss Analysis with Experimental Verifications
Open this publication in new window or tab >>A Permanent Magnet Traction Motor for Electric Forklifts: Design and Iron Loss Analysis with Experimental Verifications
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.
Trita-EE, ISSN 1653-5146 ; 2006:59
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
urn:nbn:se:kth:diva-4241 (URN)978-91-7178-520-6 (ISBN)
Public defence
2006-12-19, M3, KTH, Brinellvägen 64, Stockholm, 10:15
QC 20100903Available from: 2006-11-15 Created: 2006-11-15 Last updated: 2010-09-03Bibliographically approved

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