1,720,967 research outputs found
Fast Computation Method for Stator Winding Skin-Effect Additional Losses in Synchronous Machines with Open Slots and Arbitrary Rotor Geometry
No full textLarge medium-voltage electric machine stators are usually equipped with form wound coils made of flat conductors (strands) and embedded in open (rectangular) slots. Air-gap magnetic flux lines can enter the slot and, sweeping the strands placed nearest the slot opening, induce eddy currents in them. Such eddy currents cause additional losses which can be much higher than usual skin-effect and proximity losses. In order to avoid dangerous overheating and hot spots, the additional losses in question need to be carefully predicted in the design stage. Time-stepping finite-element analysis (TSFEA) can be used for the purpose, which however implies a large computational burden and requires the machine geometry to be modeled in detail. This article proposes alternative methods based on time-harmonic finite-element analysis (THFEA) simulations performed on highly simplified machine models and with no need to take rotor motion into account. The proposed methods are shown to produce very accurate results, compared to TSFEA, but with very significant time and computational savings
Potentials and limits of three-phase fractional-slot concentrated winding optimization
No full textFractional-slot concentrated windings (FSCWs) in three-phase permanent magnet machines are popular for several advantages but may cause severe performance issues due to their richness in air-gap magneto-motive force (MMF) space harmonics. This paper intends to explore the potentials and limits of FSCW optimization through multi-layer arrangements when applied to mitigate three problems, namely: permanent-magnet eddy-current losses, unbalanced magnetic pull (UMP) and torque ripple. It shows that, regardless of the algorithm adopted, the winding optimization is effective only on well-defined slot-pole combinations, which are strongly different depending what the optimization target is. Permanent magnet loss minimization is shown to be the field where the most effective results can be achieved, while UMP and torque ripple can be mitigated by winding optimization to a smaller extent and for a limited set of slot-pole combinations
On the analytical determination of the complex relative permeance function for slotted electrical machines
No full textThe complex relative permeance function is a suitable tool to predict the air gap magnetic field in slotted stator electrical machines. In the literature, the complex permeance function is usually identified by means of numerical techniques based on complex approaches such as conformal mapping or subdomain method. In this paper, an alternative approach is proposed. This method is based on solving the magnetostatic Laplace equation over a portion of the slotted air gap by imposing appropriate boundary conditions in the slot opening region. Such boundary condition tries to represent the theoretical trend of the magnetic field divergence near the corner-shaped ferromagnetic regions. The Carter theory for the slot fringing effect is also used. A fully analytical formulation for the complex relative permeance function is obtained, and its accuracy is assessed by comparison with Finite Element Analysis (FEA)
FEA-Assisted steady-state modelling of a spoke type IPM machine with enhanced flux weakening capability
Full text linkInterior permanent magnet (IPM) machines with spoke-type design are possible candidates for various applications, including vehicle traction. One of their drawback is the high demagnetizing current required in the flux weakening region to let the motor achieve high speeds. This problem can be mitigated by equipping the motor with a mechanical devices consisting of mobile rotor yokes. These move radially by centrifugal force so as to reduce the air-gap flux at high speed with no need for demagnetizing current injection. This paper addresses the problem of modeling such IPM motor to study its steady-state behavior under different operating conditions, both in the full-flux and in the flux-weakening region of the speed range. The approach uses a limited set of non-linear finite element analysis to characterize the dependency of motor flux linkages on the stator currents and rotor position. Interpolating functions are then obtained to mathematically capture this dependency and plug it into the steady-state electromechanical equations of the motor. The effectiveness and accuracy of the method are assessed through on-load measurements taken on the modelled motor both in low and high speed operation
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Analytical-based iron loss assessment in the SPM slotless machine stator core
No full textThe use of slotless machines has acquired growing interest when features such as low vibrations and noise, along with low losses at high speed, are required. However, a careful assessment of the iron losses in the stator core will be relevant already in the design or pre-design phase. Standard methodologies for the iron losses estimation are typically FE analysis with constant loss coefficients, which can lead to weak extrapolations with huge errors. In this paper, an analytical method for iron losses prediction is derived. It is based on the extension of the field solution in the stator iron core, where an accurate 2-D field solution of the slotless machine topology is found. The analytical solution is combined with a variable loss coefficients model, which can be efficiently computed by vectorized post-processing. The case study proves that the approach can predict all of the loss phenomena over a wide operating range with improved precision
Analytical Iron Loss Evaluation in the Stator Yoke of Slotless Surface-Mounted PM Machines
Full text linkOne of the attractive benefits of slotless machines is low losses at high speeds, which could be emphasized by a careful stator core loss assessment, potentially available already at the pre-design stage. Unfortunately, mainstream iron loss estimation methods are typically implemented in the finite element analysis (FEA) environment with a constant-coefficients dummy model, leading to weak extrapolations with huge errors. In this paper, an analytical method for iron loss prediction in the stator core of slotless PM machines is derived. It is based on the extension of the 2-D field solution over the entire machine geometry. Then, the analytical solution is combined with variable- or constant-coefficient loss models, which can be efficiently computed by vectorized post-processing. Our case study compares different approaches to predict the loss phenomena. Moreover, the paper proposes a lookup-table-based (LUT) solution as an alternative approach. For validation purposes, the models are matched against a sufficiently dense dataset of 180 measured loss points for a lamination sample in the Epstein frame, covering a wide range of frequencies and flux density levels, which are usually not available from commercial datasheets. Finally, all the methods are compared for the slotless machine case, highlighting that the LUT method depends on a sufficiently dense experimental dataset to achieve satisfactory accuracy.Analytical Iron Loss Evaluation in the Stator Yoke of Slotless Surface-Mounted PM MachinesacceptedVersio
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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