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1.
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: 460; Prenosov: 0
.pdf Celotno besedilo (1,69 MB)

2.
Thermal regime of annual air temperature in Bosnia and Herzegovina
Nusret Drešković, Ranko Mirić, 2017, izvirni znanstveni članek

Opis: Horizontal air temperature is defined by the value of the mean air temperature for a certain surface area unit. It is defined by the value of horizontal thermal gradient, i.e. the value of average change of horizontal temperature per unit area. In order to define the horizontal change of air temperature in Bosnia and Herzegovina, a GRID thermal model was constructed whose spatial resolution is 20 m. Based on obtained thermal model geo-database it was determined that the mean annual air temperature for the whole area of Bosnia and Herzegovina is about 10.9 °C, keeping in mind that there are significant thermal differences with respect to the two existing climate zones. More specifically, on the territory of the northern temperate climate zone the average annual temperature is about 9.7 °C, while in the Mediterranean climate zone the said value is 12.1 °C. In this work, it was also found that thermal contrasts are very pronounced as well, due to the fact that average annual temperature in the highest mountain peak zones in southeastern Bosnian highlands is negative and is found to be -1.4 °C (Maglić peak), while at the Neum coastal zone it is measured at 15.9 °C. The above stated pronounced thermal contrasts are determined on a small horizontal distance, as a consequence of climactic position of Bosnia and Herzegovina as well as highly pronounced terrain dynamics.
Ključne besede: Bosnia and Herzegovina, horizontal thermal gradient, GRID thermal model, climate zones, average annual air temperature
Objavljeno v DKUM: 17.04.2018; Ogledov: 984; Prenosov: 71
.pdf Celotno besedilo (1,15 MB)
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3.
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: 949; Prenosov: 324
.pdf Celotno besedilo (1,32 MB)
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4.
The combined analysis of phonon and electron heat transfer mechanism on thermal conductivity for nanofluids
Jurij Avsec, 2008, izvirni znanstveni članek

Opis: The paper features the mathematical model representing the analytical calculation of phonon and electron heat transfer analysis of thermal conductivity for nanofluids. The mathematical model was developed on the basis of statistical nanomechanics. We have made the detailed analysis of the influence of temperature dependence on thermal conductivity for nanofluids. On this basis are taken into account the influences such as formation of nanolayer around nanoparticles, the Brown motion of solid nanoparticles and influence of diffusive-ballistic heat transport. The analytical results obtained by statistical mechanics are compared with the experimental data and they show relatively good agreement.
Ključne besede: statistical nanomechanics, phonons, electron heat transfer, nanofluids, thermal conductivity, thermodynamic properties, mathematical model, statistical nanomechanics
Objavljeno v DKUM: 31.05.2012; Ogledov: 1961; Prenosov: 98
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5.
The calculation of thermal conductivity, viscosity and thermodynamic properties for nanofluids on the basis of statistical nanomechanics
Jurij Avsec, Maks Oblak, 2007, izvirni znanstveni članek

Opis: The paper features the mathematical model of calculation of thermophysical properties for nanofluids on the basis of statistical nanomechanics. Calculation of properties for nanofluids for real substances is possible by the classical and statistical mechanics. Classical mechanics has no insight into the microstructure of the substance. Statistical mechanics, on the other hand, calculates the properties of state on the basis of molecular motions in a space, and on the basis of the intermolecular interactions. The equations obtained by means of classical thermomechanics are empirical and apply only in the region under observation. The main drawback of classical thermomechanicsis that it lacks the insight into the substance of microstructure. Contrary to classical mechanics, statistical mechanics calculates the thermomechanic properties of state on the basis of intermolecular and intramolecular interactions between particles in the same system of molecules. It deals with the systems composed of a very large number of particles. The results of the analysis are compared with experimental data and show a relatively good agreement. The analytical results obtained by statistical mechanics are compared with the experimental data and show relatively good agreement.
Ključne besede: statistical thermodynamics, thermophysical properties, viscosity, thermal conductivity, thermodynamic properties, mathematical model, nanofluids, statistical nanomechanics
Objavljeno v DKUM: 31.05.2012; Ogledov: 1852; Prenosov: 125
URL Povezava na celotno besedilo

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