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1.
The development of ARM-based portable and adaptable power supply
Tomislav Brlek, 2019, master's thesis

Abstract: This master’s thesis describes a development of a portable and adjustable power supply. The first part of the thesis introduces us to the working principle of power supplies in general. Next, we present a functional design of a portable and adjustable power supply and a list of its required functionalities. Chapter “switched-mode power supplies” introduces us to the theoretical basics of the said power supplies, while chapter “linear regulators” introduces us to different types of linear regulators and tells us more about how they work. Everything regarding which microcontroller was used and why it was used is described in the “ARM microcontroller” chapter. Besides microcontrollers, it also talks about which integrated development environment is used and how the microcontroller is programmed. A full and detailed description of each part of the analog circuitry can be found in the chapter “describing the development of the portable and adjustable power supply”. Lastly, the user interface is described in detail.
Keywords: portable power supply, ARM processor, variable laboratory bench power supply, LCD touchscreen, energy efficient, lithium battery, battery charger, voltage control
Published: 13.11.2019; Views: 393; Downloads: 67
.pdf Full text (3,85 MB)

2.
Exergy analysis of a Brayton cycle with variable physical properties and variable composition of working substance
Marija Živić, Antun Galović, Jurij Avsec, Mario Holik, 2016, original scientific article

Abstract: The exergy analysis of a Brayton cycle is performed in the paper. The four input variables: the ratio of the compressor exit and inlet pressures, the ratio of inlet temperature of gases in turbine and inlet temperature of air in compressor and the isentropic efficiencies of the compressor and turbine are analysed. The temperature ratio is varied in a way that the compressor inlet temperature of air is maintained constant, while the turbine inlet temperature of flue gases is varied from 900 to 1200°C. In the combustion chamber methane is completely combusted with excess air ratio which is determined by the temperature of flue gases at the turbine inlet. The analysis further includes variability of the molar heat capacities of air and flue gases with temperature and variability of their heat capacity ratios. The exergy destruction in turbine, compressor and combustion chamber and also total exergy efficiency of the cycle are considered in the analysis.
Keywords: Brayton cycle, variable physical properties, variable composition of working substance, maximum work output, maximum thermal efficiency
Published: 12.07.2017; Views: 1252; Downloads: 266
.pdf Full text (789,62 KB)
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3.
SOFT SWITCHING FOR IMPROVING THE EFFICIENCY AND POWER DENSITY OF A SINGLE-PHASE CONVERTER WITH POWER FACTOR CORRECTION
Tine Konjedic, 2015, doctoral dissertation

Abstract: This thesis investigates the possibilities for increasing the power conversion efficiency and power density of a single-phase single-stage AC-DC converter with power factor correction capability. Initially, the limitations are investigated for simultaneous increase of power density and efficiency in hard switched bidirectional converters. The switching frequency dependent turn-on losses of the transistors have been identified as the main limiting factor. In order to avoid the increase in total power losses with increasing the switching frequency, a control approach is proposed for achieving zero voltage switching transitions within the entire operating range of a bidirectional converter that utilizes power transistors in a bridge structure. This approach is based on operation in the discontinuous conduction mode with a variable switching frequency. Operation in the discontinuous conduction mode ensures the necessary reversed current that naturally discharges the parasitic output capacitance of the transistor and thus allows this transistor to be turned on at zero voltage. On the other hand, the varying switching frequency ensures that the converter operates close to the zero voltage switching boundary, which is defined as the minimum required current ripple at which zero voltage switching can be maintained. Operation with the minimum required current ripple is desirable as it generates the lowest magnetic core losses and conduction losses within the power circuit. The performance and effectiveness of the investigated approach were initially verified in a bidirectional DC-DC converter. A reliable zero voltage switching was confirmed over the entire operating range of a bidirectional DC-DC converter, as well as the absence of the reverse recovery effect and the unwanted turn-on of the synchronous transistor. In order to justify its usage and demonstrate its superior performance, the proposed zero voltage switching technique was compared with a conventional continuous conduction mode operation which is characterized by hard switching commutations. After successful verification and implementation in a bidirectional DC-DC converter, the investigated zero voltage switching approach was adapted for usage in an interleaved DC-AC converter with power factor correction capability. Comprehensive analysis of the converter's operation in discontinuous conduction mode with a variable switching frequency was performed in order to derive its power loss model. The latter facilitated the design process of the converter's power circuit. A systematic approach for selecting the converter's power components has been used while targeting for an extremely high power conversion efficiency over a wide operating range and a low volume design of the converter. The final result of the investigations performed within the scope of this thesis is the interleaved AC-DC converter with power factor correction capability. Utilization of interleaving allows for increasing the converter's power processing capability, reduces the conducted differential mode noise and shrinks the range within which the switching frequency has to vary. The proposed zero voltage switching control approach was entirely implemented within a digital signal controller and does not require any additional components within the converter's circuit. The experimental results have confirmed highly efficient operation over a wide range of operating powers. A peak efficiency of 98.4 % has been achieved at the output power of 1100 W, while the efficiency is maintained above 97 % over the entire range of output powers between 200 W and 3050 W.
Keywords: zero-voltage switching, power factor correction, variable switching frequency, discontinuous conduction mode, reverse recovery, unwanted turn-on, bidirectional DC-DC converter, bidirectional AC-DC converter, control of switching power converters
Published: 13.10.2015; Views: 1456; Downloads: 164
.pdf Full text (23,37 MB)

4.
The multilevel MINLP optimization approach to structural synthesis: the simultaneous topology, material, standard and rounded dimension optimization
Stojan Kravanja, Simon Šilih, Zdravko Kravanja, 2005, original scientific article

Abstract: The paper describes the simultaneous topology, material, standard and rounded dimension optimization of mechanical structures, performed by the Mixed-Integer Non-linear Programming (MINLP) approach. Beside the generation of an MINLP mechanical superstructure, the development of a general multilevel MINLP formulation for a mechanical superstructure is presented. The consideration of the discrete materials as well as standard and particularly rounded dimensions in structural synthesis significantly increases the combinatorics of the discrete optimization, which as a result may become too difficult to solve. A Linked Multilevel Hierarchical Strategy (LMHS) has been introduced for the solving of such large combinatorial problems. In order to decrease the effect of non-convexities, the Modified Outer-Approximation/Equality-Relaxation (OA/ER) algorithm has been applied. Four numerical examples of different complexities are presented to illustrate the proposed multilevel MINLP optimization approach: the optimization of two steel trusses, a composite I beam and a hydraulic steel roller gate Intake gate, erected in Aswan II, Egypt.
Keywords: structural optimization, structural synthesis, MINLP, topology opitmization, material optimization, discrete variable optimization, multilevel MINLP strategy, truss, composite beam, roller gate
Published: 01.06.2012; Views: 1961; Downloads: 82
URL Link to full text

5.
Improvement of the statical behaviour of pressure controlled axial piston pumps
Darko Lovrec, Edvard Detiček, 2009, original scientific article

Abstract: The control of pressure by means of variable displacement pumps is one of the most important tasks in the field of pump control, which is influenced by the properties of the pumps. Looking for a suitable control concept with good static behaviour, a method is tested which tunes the parameters of a controller. Instancing a variable displacement axial piston pump controlled bya 3/2 proportional valve the improvement will be achieved by fuzzy logic on the one hand and a non-linear approach - adaptation of gain of the classical controller - on the other.
Keywords: servo hydraulic, variable displacement pump, pressure control, conventional control structures, fuzzy control structures, nonlinear control structures
Published: 31.05.2012; Views: 1171; Downloads: 35
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