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Comparison of different stator topologies for BLDC drives : master's thesis
Mitja Garmut, 2020, magistrsko delo

Opis: The focus of this Master's thesis was to increase the output-power density of a fractional-horsepower BLDC drive. Different stator segmentation topologies were analyzed and evaluated for this purpose. The presented analysis was performed by using various models with different complexity levels, where a Magnetic Equivalent Circuit (MEC) model and a 2D transient Finite Element Method (FEM) model combined with a power-loss model, were applied systematically. Characteristic behavior of the BLDC drive was obtained in this way. The models were validated with measurement results obtained on an experimental test drive system. The influence of the weakening of the magnetic flux density and flux linkage, due to segmentation were analyzed based on the validated models. Furthermore, the increase of the thermal-stable output power and efficiency was rated, due to the consequently higher slot fill factor. Lastly, a detailed iron-loss analysis was performed for different stator topologies. The performed analysis showed that segmentation of the stator can enable a significant increase of the output power of the discussed BLDC drives, where the positive effects of segmentation outweigh the negative ones from the electromagnetic point of view. Segmentation, however, also impacts other domains, such as Mechanical and Thermal, which was out of the scope of this thesis, and will be performed in the future.
Ključne besede: fractional-horsepower BLDC drive, stator segmentation, fill factor increase, thermal-stable output power, Finite Element Method model
Objavljeno v DKUM: 17.11.2020; Ogledov: 659; Prenosov: 0
.pdf Celotno besedilo (1,69 MB)

Simulation-based Evaluation of Frequency Response Analysis as a Diagnostic Tool for Deformations of Windings in Power Transformers : master's thesis
Ivan Papa, 2020, magistrsko delo

Opis: In this master’s thesis, we have established a model of a transformer winding. This model is based on the multi transmission line theory that allows us to model each turn of the winding separately. By using that approach, it was possible to calculate the frequency response of a winding in the required frequency range from 20 Hz to 2 MHz. The purpose of this simulation was to evaluate the frequency response analysis as a diagnostic tool for deformations of windings in power transformers. An evaluation was performed using sensitivity analysis of several parameters that indicate winding deformations. Finally, axial bending deformation was simulated and successfully diagnosed by applying the frequency response analysis.
Ključne besede: Power transformer, Frequency response analysis, Diagnostics, MTL model
Objavljeno v DKUM: 03.11.2020; Ogledov: 511; Prenosov: 55
.pdf Celotno besedilo (2,64 MB)

MOS-FET as a current sensor in power electronics converters
Rok Pajer, Miro Milanovič, Branko Premzel, Miran Rodič, 2015, izvirni znanstveni članek

Opis: This paper presents a current sensing principle appropriate for use in power electronics’ converters. This current measurement principle has been developed for metal oxide semiconductor field effect transistor (MOS-FET) and is based on UDS voltage measurement. In practice, shunt resistors and Hall effect sensors are usually used for these purposes, but the presented principle has many advantages. There is no need for additional circuit elements within high current paths, causing parasitic inductances and increased production complexity. The temperature dependence of MOS-FETs conductive resistance RDS−ON is considered in order to achieve the appropriate measurement accuracy. The “MOS-FET sensor” is also accompanied by a signal acquisition electronics circuit with an appropriate frequency bandwidth. The obtained analogue signal is therefore interposed to an A-D converter for further data acquisition. In order to achieve sufficient accuracy, a temperature compensation and appropriate approximation is used (RDS−ON = RDS−ON(Vj)). The MOS-FET sensor is calibrated according to a reference sensor based on the Hall-effect principle. The program algorithm is executed on 32-bit ARM M4 MCU, STM32F407.
Ključne besede: power electronics, converters, MOS-FET, current measurement, thermal model
Objavljeno v DKUM: 22.06.2017; Ogledov: 1073; Prenosov: 344
.pdf Celotno besedilo (1,32 MB)
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On new approach to rheological modeling of an electrostatic ash and water - quadratic law
Primož Ternik, 2002, objavljeni znanstveni prispevek na konferenci

Opis: In the paper a new rheological model for an electrostatic ash and water mixture is proposed. The fundamental equation of the rheological model was used to determine the relationship between the shear stress and the shear rate as well as the equation of a velocity profile for the flow through a straight pipe. Experimental results obtained from a capillary viscometer were used as the basis to determine the parameters for the proposed model by the non-linear regression analysis. With the Quadratic law a numerical analysis of a mixture flow through a capillary pipe with the finite volume method was performed. The derived equations for the velocity profile, shear stress and shear rate were validated through a comparison of numerically obtained and theoretical results. Finally, the compariosn between the Quadratic and the Power law is presented.
Ključne besede: fluid mechanics, non-Newtonian fluids, mixture of electrofilter ash and water, flow in pipes, capillary pipes, rheological model, velocity profile, shear stress, finite volume method, numerical analysis, quadratic law, power law, mehanika fluidov
Objavljeno v DKUM: 01.06.2012; Ogledov: 2038; Prenosov: 43
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