In recent years, the interest for parallel multicell converters has grown, which is partially due to the possibility of coupling the inductors used to connect the different commutation cells together. Coupling the inductors to form an InterCell Transformer (ICT) does not usually modify the output current, but it reduces the current ripple in the windings and the flux swing in some regions of the core. It can be shown that this brings a reduction of copper and core losses in the magnetic component. The reduction of the phase current ripple also reduces the difference between turn on and turn off current in the switches, which brings a reduction of switching losses for devices generating more losses at turn off than at turn on. The design of an ICT is not that different from any other magnetic component but it is very specific and inherent features must be taken into account. Taking full benefit of the potential advantages of ICTs requires the development of special tools and methods which are the focus of the study. We show how to design ICTs considering several topologies and different methods, from the most precise and time-consuming to the less accurate but more quickly calculated. The explanation of the ICT design is divided in four main parts: Copper Losses, Core Losses, Flux Density Saturation and Thermal Aspects. Further attention is given to high frequency copper losses since complex phenomena such as skin and proximity effects highly influence the ICT design. Based on Finite Element Method simulations, smart practices are suggested to reduce high and low frequency copper losses, not only in ICTs but also in inductors and transformers. Simple tables are developed to help transformer designers to identify the best configuration of conductors inside a given core window, depending on the current waveform and frequency, number of turns and geometrical parameters. Optimization routines to reduce the ICT total mass, volume, losses or cost are developed and multidimensional interpolation of pre-simulated values of AC resistance and leakage inductance is used to speed up the optimization routine. Comparison of ICT designs with regard to core and conductor material, number of cells and switching frequency is performed. Comparison with regular inductors is also made in order to verify the benefits of this kind of magnetic component. Multilevel converter control aspects applied to three- hase systems is also investigated in terms of the ICT flux. Zero sequence signals, specific for a PWM strategy and converter/load topology, are created in order to minimize the flux in ICTs and consequently reduce even further the mass and size of these components. Comparison between several PWM methods are performed and experimentally verified.

Les systèmes de communication sans fil en fréquences millimétriques ont gagné considérablement en importance au cours des dernières années. Des applications comme les réseaux WLAN et WPAN à 60 GHz, le radar automobile autour de 80 GHz ou l’imagerie à 94 GHz sont apparues, demandant un effort conséquent pour la conception des circuits intégrés émetteurs et récepteurs sur silicium. Dans ce contexte, les transformateurs intégrés sont particulièrement intéressants. Ils peuvent réaliser des fonctions comme l’adaptation d’impédance, la conversion du mode asymétrique au différentiel et la combinaison de puissance. La conception et la modélisation de ce type de transformateur font le sujet de cette thèse. Une étude détaillée des topologies de transformateurs est présentée, concernant le dessin des inductances, leur position relative, leurs dimensions géométriques, le blindage du substrat et l’obtention de rapports importants de transformation. Leur modélisation par des simulations électromagnétiques et par un circuit électrique à éléments discrets est également discutée. Le modèle présente une topologie 2-π et une série d’équations analytiques dépendant de ses caractéristiques technologiques et géométriques pour évaluer tous ses composants. Un très bon accord entre les simulations et les mesures est observé pour des transformateurs en technologies CMOS 65 nm et BiCMOS 130 nm jusqu’à 110 GHz. Finalement, les transformateurs sont appliqués à la conception d’un mélangeur BiCMOS à 77 GHz et un amplificateur de puissance CMOS à 60 GHz. / Millimeter-wave wireless communication systems have considerably gained in importance in recent years. Important applications as 60-GHz WLANs and WPANs, 80- GHz automotive radar, and 94 GHz imaging have emerged, requiring significant effort on the design of transceiver’s silicon-based integrated circuits. In this context, integrated transformers are of a particular interest. They may perform, among other functions, impedance matching, single to differential conversion, and power combination. The design and modeling of this type of transformers is the subject of this thesis. A comprehensive study on the topology of transformers is presented, regarding the layout of individual coils, their relative position, geometric dimensions, substrate shields, and the achievement of high transformation ratios. Their modeling through electromagnetic simulations and a lumped-element electric circuit is discussed as well. The model presents a 2-π topology and analytical equations depending on both technological and geometric characteristics to evaluate the totality of its components. A close agreement between model and measurement is shown for 65-nm CMOS and 130-nm BiCMOS transformers up to 110 GHz. Those transformers are then applied to the design of a 77-GHz BiCMOS mixer and a 60-GHz CMOS power amplifier.

M.Ing. (Electrical and Electronic Engineering) / Long transmission lines in power system require high line loading in order to lower voltage limits due to line losses. For relatively long lines, line charging is high and thus higher voltage limits reached at low loading. It follows then that it is a challenge to maintaining the voltages between the acceptable limits for relatively long lines. This dissertation highlights the problems experienced when load varying from very low to very high is supplied by very long parallel lines of different impedance characteristic. When the load is extremely high, there are low voltages experienced which are solved by use of shunt capacitors and/or adding more lines. When the load is extremely low, there are high voltages experienced which are solved by use of shunt reactors and/or switching some of the lines off. The type of solutions to this two loading extremes as indicated above, can be problematic, in that; new lines requires servitudes which can take too long, shunt capacitors and reactors in this type of the network is not desirable since the introduction of too many of these devices have maintenance implications and they would require continuous switching to maintain acceptable voltages, resulting in complicated operation of the network. This research proposes the use of a phase shifting transformer located on one of two parallel corridors supplying power to a load located remotely from the rest of the system. The transformer is able to rearrange the active power flows to vary loadings of the corridors and the improvements in voltage regulation can be realised during both low and high load conditions.

No description available.

Large capacity high voltage power transformers are one of the most expensive items of equipment in an electrical power network. Power utilities can ill-afford breakdown of transformers, especially, in a deregulated scenario. The consequences of such a failure are well known. Under these circumstances, utilities have figured-out that condition-based monitoring and diagnosis is worth pursuing, in spite of increased expenditure. Thus, monitoring and diagnosis is an integral part of operation and maintenance. Mechanical forces generated during short-circuits is the main cause leading to displacement/deformation of windings. Frequency response measurements have attained worldwide acceptance as a highly sensitive monitoring tool for detecting occurrence of such events. This is evident from the fact that customized commercial equipment are available (popularly called FRA or SFRA instruments), and with recent introduction of an IEEE draft trial-use guide for application and interpretation of frequency response analysis. Once a damage is detected, the next task is to identify its location along the winding and, if possible, determine its extent of severity. Understandably, these two tasks are best achieved, without disassembling the transformer and should ideally be based on off-line and on-site terminal measurements. In this regard, literature analysis reveals that recent research efforts have successfully demonstrated possibilities of using frequency response data for localization of discrete change in windings. This is indeed noteworthy, in spite of one major drawback. This pertains to excessive computing time needed to synthesize large-sized ladder-network, which automatically limits its practical use. Keeping these issues in mind, a research was initiated to find alternatives. The primary objective of this thesis is to examine the use of- • Complexnetwork-function-lociforlocalizationofadiscretechangeinasingle,isolatedtransformerwinding,basedonterminalmeasurements It goes without saying that the proposed method should be non-invasive, simple, time-efficient and overcome drawbacks in the earlier approach. A brief summary of the proposed method follows- This thesis presents a different approach to tackle the problem of localization of winding deformation in a transformer. Within the context of this thesis, winding deformation means, a discrete and specific change imposed at a particular position on the winding. The proposed method is based on the principle of pre-computing and plotting the complex network-function-loci (e.g. driving-point-impedance) at a selected frequency, for a meaningful range of values for each element (increasing and decreasing) of the ladder network. This loci diagram is called the nomogram. After introducing a discrete change (to simulate a deformation), the driving-point-impedance (amplitude and phase) is measured again .By plotting this single measurement on the nomogram, it is straightforward to estimate the location and identify the extent of change. In contrast to the earlier approach (wherein the entire ladder-network had to be synthesized for every new measurement), the proposed method overcomes the drawbacks, is non-iterative and yields reasonably accurate localization. Experimental results on a model coil and two actual transformer windings (continuous-disc and interleaved-disc) were encouraging and demonstrate its potential. Further details are presented in the thesis.

No description available.

No description available.

Customers expect electricity to be not only available but also affordable whenever they need it. Due to the stochastic nature of power system component failure, the management of power interruption is challenging. Although the reliability of supply can usually be increased by employing redundant equipment; this means that affordability is compromised. At present, many power utilities have a considerable amount of aged equipment in their networks. Although they have already started replacement planning, the price control schemes imposed by regulatory authorities constrain their capital expenditure budget. This thesis has studied the influence of the end-of-life failure of power transformers on transmission system reliability in order to make decisions on their replacement. Power transformers are selected for the analysis because they are technically complex, expensive, and main feed points of electricity for end users. In addition, surveys on ageing asset show that 50% of transformer populations, in many utilities, have been classified as old since the year 2008. The focus of these reliability analyses is to identify the most critical transformers and to establish a reliability based replacement framework. Modelling of end-of-life failure was reviewed, and the state-of-the-art method of its incorporation into system reliability was adopted. A reliability assessment tool within DIgSILENT PowerFactory package was developed in order to perform reliability studies. This thesis has four original contributions surrounding transmission system reliability analysis. The first contribution is the development of a cost-effective framework that concerns the application of reliability studies on asset replacement decision making. The developed framework has employed reliability importance measures, the Pareto analysis and economic comparison based on reliability incentive/penalty schemes. All the three elements of the framework are original applications to system reliability area. The second contribution is the integration of unconventional end-of-life failure models into system reliability. The unconventional model used in this study is Arrhenius-Weibull distribution, which characterises end-of-life failure under different loading conditions. This study has evaluated the added value provided by including loading levels in failure models and how this enhances the understanding of the effect of operational factors on system reliability. The third contribution is the investigation of dependent failure of power transformers caused by thermal stress. This investigation has led to the development of two probabilistic indicators to rank power transformer based on their criticality to multiple failure events. These new indicators have related the transformer reliability to its age and loading levels. In the fourth contribution, comprehensive studies of the effect of uncertainty associated with failure model parameters were performed. The first study has established bases for a system related approach for refining failure models. The approach is based on assessing the sensitivity of the system reliability or the system reliability applications to the uncertainty in failure model parameters. In the second study, two quantification methods were adopted to propagate the uncertainty in failure model parameters to system reliability indices. These are the second order probability and evidence theory. The last uncertainty study has described the use of sampling based sensitivity analysis to identify the most critical transformers and their area of vulnerability. Studies throughout the thesis have been performed on a realistic transmission network and the IEEE Reliability Test System.

We address the problem of estimating a high quality dense depth map from a single RGB input image. We start out with a baseline encoder-decoder convolutional neural network architecture and pose the question of how the global processing of information can help improve overall depth estimation. To this end, we propose a transformer-based architecture block that divides the depth range into bins whose center value is estimated adaptively per image. The final depth values are estimated as linear combinations of the bin centers. We call our new building block AdaBins. Our results show a decisive improvement over the state-of-the-art on several popular depth datasets across all metrics. We also validate the effectiveness of the proposed block with an ablation study.

The purpose of this thesis was to study the properties of electronic current and voltage transformers, choose the method for temperature cycle accuracy test and the development of the measuring software. Measuring software was realized in LabVIEW version 8.2. The first part describe the topic of this thesis. The second part describes various kinds of sensors and describtion of functions and specifications. The third part describe programming system LabVIEW. The fourth describe design of connection supply and measurement part of circuit. The fifth part describes used instruments. The sixth part is about used methods measuring. In the seven part is the description of the functions of this program and its control. In eight part is evaluated measurement uncertainty. In the last part are shown examples of the application program.