The conductivity is one of the main properties of HVDC cable insulation materials and needs to be evaluated carefully. Since measurement on cables is time consuming, often thin specimens and normal conductivity measurement cells are used to compare the materials. In this way however, the bulk effects will be less represented in the measurement and the results will be less representative. Instead, one needs to perform the measurements on thick plate samples and with higher voltage levels. This work focuses on the conductivity measurements on thick HVDC insulation plate samples subject to a high electric field and carefully controlled conditions. In the literature, there are many different methods of measuring the leakage current such as dielectric spectroscopy, PD, IV and PEA measurements. In this thesis a three electrode setup is used to measure the leakage current where the electrodes are placed inside the oven.  This is to be able to control both temperature and high voltage under similar and different conditions where it is possible to change these two parameters during measurement. This was made by two Labview programs; one for creating a schedule and one control program which controls the equipment in the cell.  The task was to make sure that the cell functioned by obtaining repeatable and reasonable measurements.  The results that were obtained were reasonable and verified that the cell functioned. The executed measurements were performed in order to achieve a better understanding of error factors in the measurement system, ranging from preparing the sample to measuring the leakage current. The purpose with the cell is it to investigate the quality of the HVDC insulation by conductivity measurements on millimetre thick plate samples. / Den elektriska konduktiviteten är en av de viktigaste egenskaperna av HVDC kablars isolationsmaterial, XLPE, och den måste utvärderas noggrant. Mätning på fullskaliga kablar är tidskrävande och för att jämföra material används istället ofta tunna prover och normerade konduktivitetmätningsceller. En nackdel med denna metod är att bulkeffekterna blir mindre framträdande i mätningen och resultaten kommer att vara mindre representativa. Istället måste man utföra mätningen på tjockare prover och vid högre spänning. Detta examensarbete fokuserar på mätning av ledningsförmåga hos tjocka HVDC- isolationsprover under noggrant kontrollerade förhållanden och starka elektriska fält. I litteraturen finns det många olika metoder att mäta läckströmmar på, till exempel dielektrisk spektroskopi, PD, IV och PEA mätningar för att nämna några. I denna avhandling kommer ett tre-elektrod system att användas där en temperatursensor är monterad på ena elektroden. Systemet används för att både mäta läckströmmar och temperatur vid provet. Detta gör det möjligt att kontrollera temperatur och spänning oberoende av varandra vilket gjordes med hjälp av två Labview program. Det ena för att skapa ett schema och det andra användes som kontrollprogram för att styra utrustningen i cellen. Uppgiften var att kontrollera cellens funktion genom att erhålla rimliga repeterbara mätningar. Mätningarna gav rimliga resultat vilket indikerade att cellen fungerar tillfredställande. Syftet med mätningarna var att få en bättre förståelse för felfaktorer i mätsystemet som kan vara allt från att förbereda provet till att mäta läckström. Syftet med cellen är att undersöka isolationsegenskaperna på millimetertjocka pressade XLPE prover.

Aggressive scaling of CMOS circuits in recent times has lead to dramatic increase in leakage currents. Previously, sub-threshold leakage current was the only leakage current taken into account in power estimation. But now gate leakage and reverse biased junction band-to-band-tunneling leakage currents have also become significant. Together all the three types of leakages namely sub-threshold leakage, gate leakage and reverse bias junction band-to-band tunneling leakage currents contribute to more than 25% of power consumption in the current generation of leading edge designs. Different sources of leakage can affect each other by interacting through resultant intermediate node voltages. This is called loading effect and it leads to further increase in leakage current. On the other hand, sub-threshold leakage current decreases as more number of transistors is stacked in series. This is called stack effect. Previous works have been done that analyze each type of leakage current and its effect in detail but independent of each other. In this work, a pattern dependent steady state leakage estimation technique was developed that incorporates loading effect and accounts for all three major leakage components, namely the gate leakage, band to band tunneling leakage and sub-threshold leakage. It also considers transistor stack effect when estimating sub-threshold leakage. As a result, a coherent leakage current estimator tool was developed. The estimation technique was implemented on 65nm and 45nm CMOS circuits and was shown to attain a speed up of more than 10,000X compared to HSPICE. This work also extends the leakage current estimation technique in Field Programmable Gate Arrays (FPGAs). A different version of the leakage estimator tool was developed and incorporated into the Versatile Place & Route CAD tool to enable leakage estimation of design after placement and routing. Leakage current is highly dependent on the steady state terminal voltage of the transistor, which depends on the logic state of the CMOS circuit as determined by the input pattern. Consequently, there exists a pattern that will produce the highest leakage current. This work considers all leakage sources together and tries to find an input pattern(s) that will maximize the composite leakage current made up of all three components. This work also analyzes leakage power in presence of dynamic power in a unique way. Current method of estimating total power is to sum dynamic power which is ½&#;CLVDD2f and sub-threshold leakage power. The dynamic power in this case is probabilistic and pattern independent. On the other hand sub-threshold leakage is pattern dependent. This makes the current method very inaccurate for calculating total power. In this work, it is shown that leakage current can vary by more than 8% in time in presence of switching current.

[ES] Los aisladores eléctricos de alta tensión desempeñan un papel fundamental de la red de distribución y transporte de energía eléctrica, pudiendo provocar fallos imprevistos de suministro eléctrico, dando lugar a importantes impactos socio-económicos. Las descargas disruptivas por contaminación o envejecimiento de los materiales amenazan continuamente la fiabilidad de la red eléctrica, constituyendo uno de los mayores retos para los diseñadores e ingenieros de mantenimiento de la red eléctrica. En la actualidad, no existen métodos eficaces para la monitorización continua de los niveles de envejecimiento de los materiales o de de contaminación en la superficie de los aisladores durante la operación normal, por lo tanto, se recurre al mantenimiento periódico de los mismos para garantizar la continuidad del suministro eléctrico. El desarrollo de una herramienta que permita monitorizar en tiempo real los depósitos de contaminación durante la operación normal proporcionaría información muy valiosa para el mantenimiento preventivo de los aisladores eléctricos de alta tensión y/o el seguimiento del estado superficial de los aisladores. La corriente de fuga registrada en los aisladores eléctricos podría utilizarse como una medida indirecta de los depósitos de contaminación. No obstante, además de por los depósitos de contaminación y el envejecimiento de los materiales, la medida de la corriente de fuga también se ve influenciada por una serie de factores ambientales, como temperatura, humedad, dirección y velocidad del viento entre otros. Por tanto, se pretende desarrollar una técnica de procesado para estimar la corriente de fuga asociada a los depósitos de contaminación (PLC) cancelando la influencia de las variables ambientales. / [CA] Els aïlladors elèctrics d'alta tensió exerceixen un paper fonamental de la xarxa de distribució i transport d'energia elèctrica, podent provocar errors imprevistos de subministrament elèctric, donant lloc a importants impactes socioeconòmics. Les descàrregues disruptives per contaminació o envelliment dels materials amenacen contínuament la fiabilitat de la xarxa elèctrica, constituint un dels reptes més grans per als dissenyadors i enginyers de manteniment de la xarxa elèctrica. En l'actualitat, no hi ha mètodes eficaços per a la monitorització contínua dels nivells d'envelliment dels materials o de de contaminació a la superfície dels aïlladors durant l'operació normal, per tant, es recorre al manteniment periòdic dels mateixos per garantir-ne la continuïtat del subministrament elèctric. El desenvolupament d"una eina que permeti monitoritzar en temps real els dipòsits de contaminació durant l"operació normal proporcionaria informació molt valuosa per al manteniment preventiu dels aïlladors elèctrics d"alta tensió i/o el seguiment de l"estat superficial dels aïlladors. El corrent de fugida registrat als aïlladors elèctrics podria utilitzar-se com una mesura indirecta dels dipòsits de contaminació. No obstant això, a més dels dipòsits de contaminació i l'envelliment dels materials, la mesura del corrent de fugida també es veu influenciada per una sèrie de factors ambientals, com ara temperatura, humitat, direcció i velocitat del vent entre d'altres. Per tant, es pretén desenvolupar una tècnica de processament per estimar el corrent de fugida associat als dipòsits de contaminació (PLC) cancel·lant la influència de les variables ambientals. / [EN] High-voltage electrical insulators play a fundamental role in the electricity distribution and transmission network, and can cause unforeseen power supply failures, giving rise to significant socio-economic impacts. Disruptive discharges due to contamination or aging of materials continually threaten the reliability of the electrical network, constituting one of the greatest challenges for designers and maintenance engineers of the electrical network. At present, there are no effective methods for the continuous monitoring of the levels of aging of the materials or of contamination on the surface of the insulators during normal operation, therefore, periodic maintenance is used to guarantee the continuity of electrical supply. The development of a tool that allows real-time monitoring of contamination deposits during normal operation would provide very valuable information for preventive maintenance of high-voltage electrical insulators and/or monitoring of the surface condition of the insulators. Leakage current recorded in electrical insulators could be used as an indirect measure of contamination deposits. However, in addition to the contamination deposits and the aging of the materials, the measurement of the leakage current is also influenced by a series of environmental factors, such as temperature, humidity, wind direction and speed, among others. Therefore, it is intended to develop a processing technique to estimate the leakage current associated with pollution deposits (PLC) canceling the influence of environmental variables. / Bueno Barrachina, JM. (2023). Contribución al mantenimiento de aisladores de alta tensión en servicio basado en medidas de corrientes de fuga [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/199256

Gallium Nitride (GaN) based transistors have been in the spotlight for power electronics due to promising properties like high bandgap, high breakdown field, high electron mobility, and high-frequency applications. While there are some commercial devices based on these transistors available, there is still room for improvement in these devices for widespread usage. In this project, GaN-based transistors fabricated at RISE AB were investigated. These devices had previously shown high leakage current. Different approaches taken to reduce the said leakage current were analysed. The main scope of the thesis was static electrical testing of a new batch of these transistors at room temperature, mainly investigating their leakage current. The new transistors were subjected to surface treatments and also a new in-situ dielectric layer was used. The surface treatments did not show much improvement but the in-situ grown dielectric showed almost half of the initial leakage current. In addition to this different device architectures with varying gate length, gate width, and gate to drain distance were tested and compared. It was found that devices with 3 μm gate length and 12 μm gate to drain distance showed the best performance. The blocking characteristic of the transistors was also tested and the devices could withstand up to 350V. Suggestions to further identify the sources of the leakage current are presented. Possible improvement in the design of the transistors to increase the blocking voltage is also described. / Transistorer baserade på galliumnitrid (GaN) har varit i strålkastaren för kraftelektronik på grund av lovande egenskaper som högt bandgap, högt nedbrytningsfält, hög elektronmobilitet. Dessa egenskaper gör materialet synnerligen lämpligt för komponentapplikationer vid höga effekter och, framför allt, höga frekvenser. Även om det finns några kommersiella applikationer baserade på dessa transistorer finns det fortfarande stort utrymme för förbättringar. I detta projekt undersöktes GaN-baserade transistorer tillverkade vid RISE AB. Dessa komponenter hade tidigare visat hög läckström och olika tillvägagångssätt för att minska nämnda läckström har analyserats. Transistorerna i detta projekt var ytbehandlade på ett nytt sätt och dielektirkat i styrelektroden var ocskå tillverkat på ett nytt sätt. Ytbehandlingarna visade inte mycket förbättring men det dielektrikat visade nästan hälften av den initiala läckströmmen. Utöver detta testades och jämfördes olika layouter med varierande geometri, gate-längd, gate-bredd och avstånd mellan gate/source. Det visade sig att komponenter med 3 μm gate-längd och 12 μm mellan gate och drain visade bästa prestanda. Transistorernas blockeringskaraktäristik testades också och visade sig tåla upp till 350V. Förslag för att ytterligare identifiera källorna till läckströmmen presenteras. Eventuell förbättring av utformningen av transistorerna för att öka blockeringsspänningen beskrivs också.

Power-efficient circuits are a vital step in moving towards a greener future. Battery life can get substantially improved by decreasing the amount of power a circuit needs. Lower power also leads to less excess heat generated. Electronics are within everything today – from phones and microwaves to cars! If we want to optimize the electronics to require less power, we need to understand it. In some integrated circuits that utilize bipolar transistors, it has been concluded that the main limitation regarding low-power, high-temperature operations is leakage currents that arise in reverse biased p–n junctions. There is a lack of understanding regarding the magnitude of these leakage currents, especially at higher temperatures. This thesis aims to provide an understanding of the magnitude of the leakage currents in lateral gated PNP bipolar transistors and to provide empirical models of these currents.A discussion of semiconductor physics takes place, explaining how leakage currents arise in reverse-biased pn junctions. Measurements were taken on a chip with the help of different instruments and a relay network that configured the experimental setup into different circuits while measurements were being conducted.It was shown that the leakage currents are clearly exponential to temperature, as was expected. Empirical models are created with the help of the Gauss-Newton linearization method and shown to be of the form<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?$y=%20%5Ctheta_1%20%5Cmathrm%7Be%7D%5E%7B%5Ctheta_2%5Cleft(T-%5Ctheta_4%5Cright)%7D+%5Ctheta_3$" data-classname="equation" data-title="" />,where 𝜃 are parameters for the different models.A discussion is held on the impact of the results and how to improve upon them. Numerous sources of error are discussed, and further work is recommended.

With worldwide growing demand for electric energy, there has been a great interest in exploring photovoltaic (PV) sources. For the PV generation system, the power converter is the most essential part for the efficiency and function performance. In recent years, there have been quite a few new transformerless PV inverters topologies, which eliminate the traditional line frequency transformers to achieve lower cost and higher efficiency, and maintain lower leakage current as well. With an overview of the state-of-the-art transformerless PV inverters, a new inverter technology is summarized in the Chapter 2, which is named V-NPC inverter technology. Based this V-NPC technology, a family of high efficiency transformerless inverters are proposed and detailly analyzed. The experimental results demonstrate the validity of V-NPC technology and high performance of the transformerless inverters. For the lower power level transformerless inverters, most of the innovative topologies try to use super junction metal oxide semiconductor field effect transistor(MOSFET) to boost efficiency, but these MOSFET based inverter topologies suffer from one or more of these drawbacks: MOSFET failure risk from body diode reverse recovery, increased conduction losses due to more devices, or low magnetics utilization. By splitting the conventional MOSFET based phase leg with an optimized inductor, Chapter 3 proposes a novel MOSFET based phase leg configuration to minimize these drawbacks. Based on the proposed phase leg configuration, a high efficiency single-phase MOSFET transformerless inverter is presented for the PV micro-inverter applications. The PWM modulation and circuit operation principle are then described. The common mode and differential mode voltage model is then presented and analyzed for circuit design. Experimental results of a 250 W hardware prototype are shown to demonstrate the merits of the proposed MOSFET based phase-le and the proposed transformerless inverter. New codes require PV inverters to provide system regulation and service to improve the distribution system stabilization. One obvious impact on PV inverters is that they now need to have reactive power generation capability. The Chapter 4 improves the MOFET based transformerless inverter in the Chapter 3 and proposed a novel pulse width modulation (PWM) method for reactive power generation. The ground loop voltage of this inverter under the proposed PWM method is also derived with common mode and differential mode circuit analyses, which indicate that high-frequency voltage component can be minimized with symmetrical design of inductors. A 250-W inverter hardware prototype has been designed and fabricated. Steady state and transient operating conditions are tested to demonstrate the validity of improved inverter and proposed PWM method for reactive power generation, high efficiency of the inverter circuit, and the high-frequency-free ground loop voltage. Besides the high efficiency inverter circuit, the grid connection function is also the essential part of the PV system. The Chapter 5 present the overall function blocks for a grid-connected PV inverter system. The current control and voltage control loop is then analyzed, modeled, and designed. The dynamic reactive power generation is also realized in the control system. The new PLL method for the grid frequency/voltage disturbance is also realized and demonstrate the validity of the detection and protection capability for the voltage/frequency disturbance. At last, a brief conclusion is given in the Chapter 6 about each work. After that, future works on device packaging, system integration, innovation on inverter circuit, and standard compliance are discussed. / Ph. D.

No description available.

Quantenkaskadenlaser (QCLs) wurden vor gerade zwanzig Jahren erfunden und haben seitdem stetig im weltweiten Markt der optoelektronischen Bauelemente für den Infrarot an Bedeutung gewonnen. Anwendungsbeispiele für aktuelle und potenzielle Einsatzgebiete von QCLs sind photoakustische Spektroskopie, Umweltüberwachung, Simulation von heißen Körpern, und optische Freiraumdatenübertragung. Rekord optische Leistungen von 14 W und Leistungseffizienzen zwischen 15-35 % wurden bei mittelinfraroten QCLs für Betriebstemperaturen zwischen 80-300 K erreicht. Die weitere Verbesserung dieser Eigenschaften hängt nicht nur von Aspekten wie Wärmemanagement und Chip-Packaging ab, sondern auch von Verbesserungen im Laserdesign zwecks der Reduzierung des Ladungsträgerleckstroms. Dennoch sind die verschiedenen Mechanismen und Komponenten des Leckstroms in Quantenkaskadenlasern leider noch nicht gründlich untersucht worden. Die vorliegende Arbeit liefert a realistische Beschreibung der Ladungsträgertransports in QCLs. Wir beschreiben u.a. Leckströme vom Quantentopf- in höhere Zustände und diskutieren elastische und inelastische Streumechanismen von Ladungsträgern bei mittelinfraroten Quantenkaskadenlasern. Wir illustrieren außerdem die Notwendigkeit zur Berücksichtigung der Elektronentemperatur für eine vollständigere Analyse der Ladungsträgertransporteigenschaften von Quantenkaskadenlasern. Methoden zur experimentellen Ermittlung des temperaturabhängigen Leckstroms in Quantenkaskadenlasern werden präsentiert. Unser Ansatz liefert eine Methode zur effektiven Analyse von der QCL-Leistung und Vereinfacht die Optimierung von QCL aktive Regionen. / Two decades after their invention in 1994, quantum-cascade lasers (QCLs) become increasingly important in the global infrared optoelectronics market. Photoacoustic spectroscopy, environment monitoring, hot object simulation, and free-space communication systems are selected examples of the current and potential applications of QCLs. Record optical powers as large as 14 W and power-conversion efficiencies ranging between 15-35 % have been reported for MIR QCLs for temperatures 80-300 K. Further improvement of these characteristics depends not only of aspects as heat management and chip-packaging, but also on improving the active-region design to reduce several leakage channels of charge carriers. However, mechanisms through which leakage of charge carriers affects QCLs performance have not been thoroughly researched. A better understanding of the several (non-radiative) scattering mechanisms involved in carrier transport in QCLs is needed to design new structures and optimize their performance. This work provides a realistic description of charge carriers transport in QCLs. We discuss in particular carrier leakage from QCL quantum-well confined states into higher and lower states. The two main mechanisms for non-radiative intersubband scattering in MIR QCLs are electron-longitudinal-optical-phonon scattering and interface roughness-induced scattering. We present methods for the experimental determination of the leakage current in QCLs at and above laser threshold, which allowed us to estimate the sheet distributions of conduction band states and better understand the impact of temperature activated leakage on QCLs characteristics. We found that even at temperatures low enough to neglect ELO scattering, carriers leakage due to IFR becomes significant for devices operating at high electron temperatures. Altogether, this approach offers a straightforward method to analyze and troubleshoot new QCL active region designs and optimize their performance.

Os sistemas elétricos de potência estão sujeitos a diversos tipos de sobretensões que podem causar desligamentos ou avarias nos equipamentos elétricos que o compõe, comprometendo a continuidade do fornecimento de energia elétrica aos consumidores e impactando negativamente nos índices de qualidade. Um dos dispositivos mais importantes utilizados na proteção destes equipamentos são os pára-raios, os quais podem ser classificados, no sistema elétrico brasileiro, em função de sua tecnologia: a primeira, mais antiga, utiliza carboneto de silício (SiC), a segunda e mais atual utiliza óxido de zinco (ZnO) em seus elementos internos. Os primeiros estão instalados há muitos anos, até mesmo acima de sua vida útil, sendo assim, podem apresentar falhas em campo durante a sua operação. Os pára-raios de SiC estão sendo gradativamente substituídos pelos de ZnO, pois seria economicamente inviável a sua substituição imediata. Por conseguinte, torna-se imprescindível o desenvolvimento de metodologias para avaliação do seu estado de degradação, a fim de evitar-se que estes equipamentos falhem no campo. A medição da corrente de fuga, analisando-se a sua componente de terceira harmônica, mostrou que podem obtidas informações importantes a respeito dos pára-raios de SiC, fornecendo subsídios para a elaboração de um programa de manutenção que priorize a retirada daqueles mais degradados. / Power systems are subject to many types of overvoltages that may provoke interruptions or damage in electrical equipments, compromising the continuity of electrical energy supply to consumers and impacting negatively the power quality indices. One of the most important device used to protect the electric equipments are the surge arresters, which may be classified, in Brazilian power system, by its technology: the first, more antiquated, using gapped silicon-carbide (SiC) surge arrester, and secondly and newer, zinc-oxide (ZnO) surge arrester. The devices of the first type are installed for many years, even above their lifetime, presenting, in such cases, failures in site while operating. The gapped silicon-carbide surge arresters have been substituted gradually by zinc-oxide surge arresters, because it would be economically impracticable to replace them immediately. Therefore, the development of methodologies to evaluate their degradations condition is necessary, in order to avoid the failure of these equipments in site. Measurements of leakage current with third order harmonic analysis showed that important information regarding gapped silicon carbide surge arresters may be obtained, providing subsidies to elaborate a program of maintenance that prioritize the replacement of the most degraded ones.

Os sistemas elétricos de potência estão sujeitos a diversos tipos de sobretensões que podem causar desligamentos ou avarias nos equipamentos elétricos que o compõe, comprometendo a continuidade do fornecimento de energia elétrica aos consumidores e impactando negativamente nos índices de qualidade. Um dos dispositivos mais importantes utilizados na proteção destes equipamentos são os pára-raios, os quais podem ser classificados, no sistema elétrico brasileiro, em função de sua tecnologia: a primeira, mais antiga, utiliza carboneto de silício (SiC), a segunda e mais atual utiliza óxido de zinco (ZnO) em seus elementos internos. Os primeiros estão instalados há muitos anos, até mesmo acima de sua vida útil, sendo assim, podem apresentar falhas em campo durante a sua operação. Os pára-raios de SiC estão sendo gradativamente substituídos pelos de ZnO, pois seria economicamente inviável a sua substituição imediata. Por conseguinte, torna-se imprescindível o desenvolvimento de metodologias para avaliação do seu estado de degradação, a fim de evitar-se que estes equipamentos falhem no campo. A medição da corrente de fuga, analisando-se a sua componente de terceira harmônica, mostrou que podem obtidas informações importantes a respeito dos pára-raios de SiC, fornecendo subsídios para a elaboração de um programa de manutenção que priorize a retirada daqueles mais degradados. / Power systems are subject to many types of overvoltages that may provoke interruptions or damage in electrical equipments, compromising the continuity of electrical energy supply to consumers and impacting negatively the power quality indices. One of the most important device used to protect the electric equipments are the surge arresters, which may be classified, in Brazilian power system, by its technology: the first, more antiquated, using gapped silicon-carbide (SiC) surge arrester, and secondly and newer, zinc-oxide (ZnO) surge arrester. The devices of the first type are installed for many years, even above their lifetime, presenting, in such cases, failures in site while operating. The gapped silicon-carbide surge arresters have been substituted gradually by zinc-oxide surge arresters, because it would be economically impracticable to replace them immediately. Therefore, the development of methodologies to evaluate their degradations condition is necessary, in order to avoid the failure of these equipments in site. Measurements of leakage current with third order harmonic analysis showed that important information regarding gapped silicon carbide surge arresters may be obtained, providing subsidies to elaborate a program of maintenance that prioritize the replacement of the most degraded ones.