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Reaktiv effekt i Dala Energis framtida mellanspänningsnät / Reactive power in the future medium voltage grid of Dala EnergiWelbourn, Mark January 2019 (has links)
Dala Energi has large-scale plans for grid development and wants to have a better understanding of their current reactive power levels along with a future prognosis based on their plans. Changes in line inductance, shunt capacitance, area and placement put Dala Energi on the path to higher charging currents and higher reactive power generation. In addition to causing concerns in their own grid, the increased reactive power generation can present challenges for the owner of the overlying grid. Transmission of reactive power upwards is not permitted in the current contract. Dala Energi’s grid is divided into 3 separate regions with a total of 19 larger substations, 12 of which are points of connection with the overlying grid. At times, 8 of the substations have transmitted reactive power upward and soon it will be all 12. Region 1, where the 20-kV grid is located, is the biggest problem-area today, with upward-transmissions of 1 to 3 MVAr quite common and a considerable increase expected. Region 3 contains more than double the underground cable as the other two areas and might have had much greater side effects from the high shunt capacitance were it not for 3 industrial customers who consume a large portion of reactive power. In the coming years, however, Region 3 is expected to have capacitive reactive power levels nearly equal to those of Region 1. The combined reactive power baseline for all regions is expected to drop by 8.24 MVAr in the coming years. The owner of the overlying grid controls Dala Energi’s 5 largest capacitor banks which have a rated capacity of 11.6 MVAr. With the entire capacity almost always connected, the upward transmission of reactive power becomes much greater. It would be very advisable to meet with the owner, discuss interaction between the two grids and examine the details of the current contract. Compensation for excessive generation of reactive power is needed and is going to be essential in the future. The short-term variation of reactive power levels is so great that the use of fixed rating shunt reactors is ill-advised, especially under the current contract. Compensation with variable shunt reactors is recommended.
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DC/AC inverter based switched capacitor circuit topology with reduced number of components for low power applicationsBin Mohd Rozlan, Mohd Helmy Hakimie January 2017 (has links)
This thesis presents a new DC/AC inverter circuit which is based on a switched-capacitor circuit topology with reduced components (power switch and capacitor) count for low power applications. The proposed circuit has distinct features of both voltage boost-up and near sinusoidal (multi-level/staircase) AC output voltage. The main idea is to utilise a simple circuit technique called resonant-based Double Switch Single Capacitor Switched-Capacitor (DSSC SCC) with variable duty cycle Pulse Width Modulation (PWM) control technique in such a way that multi-level voltage can be realised across a capacitor. In order to show the superiority of the applied technique, comparisons with other techniques/circuits configurations are presented. The circuit technique can significantly reduce the number of multiple stages of switched-capacitor circuit cells of the recent switched-capacitor multi-level inverter topology. The proposed inverter (with integrated DSSC SCC technique) can generate a line-frequency with 13-levels near sinusoidal AC output voltage with low total harmonics distortion. The output voltage can be achieved with the least number of components use and only a single DC source is used as an input. The proposed inverter topology is also reviewed against other inverter-based switched-capacitor circuit topology and the well-known multi-level inverter topology. The proposed inverter has shown a tremendous reduction in the total harmonics distortion and circuit component count in comparison with the recent Switched-Capacitor Boost multi-level inverter and the classical Cascaded H-Bridge multi-level inverter. Mathematical analysis shows the design of the proposed inverter and PSPICE simulation result to verify the design is also presented. The practical experiment implementation of the proposed system is presented and proves the correct operation of the proposed inverter topology by showing consistency between simulation results and practical results.
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Estudo das propriedades dielÃtricas da matriz CaBi4Ti4O15 (CBT) adicionada com Bi2O3 para aplicaÃÃo em dispositivos de RF e microondas / Study of Dielectric Properties of Matrix CaBi4Ti4O15 (CBT) Bi2O3 added for applications in RF and microwave devicesDaniel Barros de Freitas 20 August 2012 (has links)
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Com os recentes avanÃos da indÃstria de telecomunicaÃÃes se faz cada vez mais necessÃrio o desenvolvimento de matÃrias que apresentem altos valores de constante dielÃtrica, baixa perda dielÃtrica e uma boa estabilidade tÃrmica. Muitos materiais para rÃdio frequÃncia e microondas tÃm sido amplamente usados em uma variedade de aplicaÃÃes nestes segmentos. Destas aplicaÃÃes, as mais recentes tecnologias utilizam cerÃmicas com baixa temperatura de sinterizaÃÃo, materiais de baixo ponto de fusÃo, alÃm das caracterÃsticas citadas anteriormente. CerÃmicas dielÃtricas a base de Bismuto sÃo candidatas como materiais de baixa temperatura de sinterizaÃÃo e tÃm sido estudadas amplamente. Este trabalho apresenta o desenvolvimento e caracterizaÃÃo da sÃrie cerÃmica CaBi4Ti4O15 (CBT) com adiÃÃo em massa de triÃxido de bismuto, material conhecido por suas excelentes propriedades dielÃtricas, principalmente elevados valores de constante dielÃtrica. Esta sÃrie foi produzida a partir do mÃtodo cerÃmico convencional ou mÃtodo do estado sÃlido, com a utilizaÃÃo de moagem mecÃnica de alta energia e tratamento tÃrmico. ApÃs a sÃntese, foi adicionado o triÃxido de bismuto em diferentes concentraÃÃes para melhorar as caracterÃsticas elÃtricas desta matriz cerÃmica. A caracterizaÃÃo estrutural foi realizada por meio de DifraÃÃo de Raios-X com Refinamento de Rietveld. Um estudo da morfologia foi realizado atravÃs de Microscopia EletrÃnica de Varredura. Foram realizados experimentos para verificar o comportamento dielÃtrico das amostras, na regiÃo de rÃdio frequÃncia e microondas. No geral percebemos que esta matriz cerÃmica apresenta as caracterÃsticas desejÃveis para sua aplicaÃÃo na fabricaÃÃo de dispositivos eletrÃnicos como capacitores e antenas ressoadoras dielÃtricas. / With the recent advances in telecommunications industry, itâs increasingly required the development of materials which have high values of dielectric constant, low dielectric loss and a good thermal stability. Many materials for radio frequency and microwaves utilization have been largely used in a variety of applications in these segments. From these applications, the latest technology generally use ceramics with low sintering temperature, low melting point materials, in addition to the aforementioned characteristics. Dielectric ceramics based on Bismuth are candidates as low temperature sintering materials and have been studied extensively. This work presents the development and characterization of ceramic series CaBi4Ti4O15 (CBT) with addition of bismuth trioxide, which is currently known for its excellent dielectric properties, mostly by its high dielectric constant values. These series were produced by the use of conventional ceramic method or method of solid state, with the use of mechanical grinding of high energy and heat treatment. After the synthesis, was added the bismuth trioxide in different concentrations to improve the electrical characteristics of ceramic CBT. The Structural characterization was showed by X-ray Diffraction with Rietveld Refinement. A study of the morphology was accomplished by scanning electron microscopy (SEM). Experiments were performed to verify the behavior of dielectric samples, radio frequency and microwaves. In general we can realize that this ceramic standard mold presents desirable characteristics for its application in the manufacture of electronic devices such as capacitors and dielectric resonator antennas.
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TÃcnica de ModulaÃÃo Aplicada Ãs Estruturas de Inversores MultinÃveis com Neutro Grampeado e Capacitor Flutuante Para ReduÃÃo de Perdas e DistorÃÃo HarmÃnica / Modulation technique applied to neutral point-clamped and floating capacitor multilevel inverters structures for losses reduction and harmonic distortion improvementGustavo Alves de Lima Henn 30 April 2012 (has links)
CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Visando superar os desafios inerentes à conversÃo de energia elÃtrica em sistemas de alta potÃncia, minimizando as perdas e melhorando a qualidade da energia processada, este tra-balho tem por objetivo analisar e implementar uma tÃcnica de modulaÃÃo para ser aplicada nas duas topologias de inversores multinÃveis mais disseminadas - com neutro grampeado (NPC), e com capacitor flutuante (FC) - a fim de reduzir os esforÃos nos semicondutores, bem como melhorar o Ãndice de distorÃÃo harmÃnica da tensÃo de saÃda. Ao longo do trabalho foi evidenciada a necessidade da digitalizaÃÃo da tÃcnica proposta, visto que o desenvolvimento analÃgico da mesma acarretaria em um circuito complexo e de baixa confiabilidade. Dessa forma, escolheu-se como plataforma digital um FPGA, devido à sua facilidade de programa-ÃÃo e reconfiguraÃÃo, alÃm da alta velocidade e quantidade de pinos de entrada e saÃda. AlÃm da tÃcnica proposta, foram tambÃm desenvolvidas outras modulaÃÃes para fins de compara-ÃÃo, apresentando os padrÃes de chaveamento para cada uma delas, bem como o comporta-mento da corrente atravÃs dos semicondutores em cada perÃodo de chaveamento. Foi tambÃm realizada a anÃlise teÃrica das topologias e suas respectivas etapas de operaÃÃo, caracterÃsticas e levantamento das equaÃÃes que ditam a anÃlise das perdas para as diferentes situaÃÃes de tÃcnicas aplicadas a cada uma das estruturas. O desenvolvimento digital das tÃcnicas mostrou-se correta atravÃs da anÃlise das formas-de-onda colhidas por meio de um circuito digital-analÃgico. AlÃm disso, a comparaÃÃo da aplicaÃÃo dessas modulaÃÃes em inversores a trÃs nÃveis NPC e FC de 6 kW mostrou-se favorÃvel à tÃcnica proposta em termos de eficiÃncia e reduÃÃo da distorÃÃo harmÃnica em ambas as topologias, comprovando sua utilidade em con-versores multinÃveis de alta potÃncia. Por fim, foi apresentado o desenvolvimento da tÃcnica proposta em inversores com mais de trÃs nÃveis, onde se pode comprovar sua eficiente aplica-ÃÃo para tais fins, bem como sua expansibilidade para inversores de n nÃveis. / In order to overcome the challenge of processing electric energy in high power systems with minimal losses and high energy quality, this work presents the implementation and anal-ysis of a modulation technique applicable on both most well-known multilevel inverter struc-tures - neutral point-clamped (NPC), and flying capacitors (FC) - to reduce the stresses across the semiconductors devices, and to improve the total harmonic distortion of the output volt-age. Throughout the work, the necessity to digitalize the proposed technique has been evi-denced due to the high complexity and low reliability inherent to the analogical approach. Thus, the digital controller FPGA has been chosen, as it is easy to program and reconfigure, works at high speed, and has a lot of input and output pins. Additionally, other modulation techniques were also implemented to compare their performance with the proposed one, pre-senting the switching patterns and the behavior of the electrical currents through the semicon-ductors for each modulation. A theoretical analysis was also performed for both topologies and their respective operation principle, characteristics, and equations used on the losses anal-ysis for the different combinations of modulation applied to each structure. Finally, the digital development of the various techniques has proved to be correct by observing the waveforms obtained through the digital/analogical circuit. Besides, the comparison of the modulation techniques on 6 kW NPC and FC three-level prototype inverters proved to be favorable to the proposed technique in terms of efficiency and total harmonic distortion reduction on both topologies, confirming its usefulness on high power multilevel converters. At last, it was pre-sented the application of the proposed modulation technique to inverters with more than three levels, where it was observed its eligibility for n-levels topologies.
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Low voltage switched capacitor circuits for lowpass and bandpass [delta sigma] convertersKeskin, Mustafa 07 December 2001 (has links)
The most accurate method for performing analog signal processing in MOS
(metal-oxide-semiconductor) integrated circuits is through the use of switched-capacitor
circuits. A switched-capacitor circuit operates as a discrete-time signal
processor. These circuits have been used in a variety of applications, such as
filters, gain stages, voltage-controlled oscillators, and modulators.
A switched-capacitor circuit contains operational amplifiers (opamps), capacitators,
switches, and a clock generator. Capacitors are used to define the state
variables of a system. They store charges for a defined time interval, and determine
the state variables as voltage differences. Switches are used to direct
the flow of charges and to enable the charging and discharging of capacitors.
Nonoverlapping clock signals control the switches and allow charge transfer between
the capacitors. Opamps are used in order to perform high-accuracy charge
transfer from one capacitor to another.
The goal of this research is to design and explore future low-voltage switched-capacitor
circuits, which are crucial for portable devices. Low-voltage operation
is needed for two reasons: making reliable and accurate systems compatible with
the submicron CMOS technology and reducing power consumption of the digital
circuits.
To this end, three different switched-capacitor integrators are proposed, which
function with very low supply voltages. One of these configurations is used to
design a lowpass ����� modulator for digital-audio applications. This modulator
is fabricated and tested demonstrating 80 dB dynamic range with a 1-V supply
voltage.
The second part of this research is to show that these low-voltage circuits are
suitable for modern wireless communication applications, where the clock and
signal frequencies are very high.
This part of the research has focused on bandpass analog-to-digital converters.
Bandpass analog-to-digital converters are among the key components in
wireless communication systems. They are used to digitize the received analog
signal at an intermediate center frequency. Such converters are used for digital
FM or AM radio applications and for portable communication devices, such as
cellular phones. The main block, in these converters, is the resonator, which is
tuned to a particular center frequency. A resonator must be designed such that
it has a sharp peak at a specific center frequency. However, because of circuit
imperfections, the resonant peak gain and/or the center frequency are degraded
in existing architectures.
Two novel switched-capacitor resonators were invented during the second
part of this research. These resonators demonstrate superior performance as
compared to previous architectures. A fourth-order low-voltage bandpass �����
modulator, using one of these resonators, has been designed. / Graduation date: 2002
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New leading/trailing edge modulation strategies for two-stage AC/DC PFC adapters to reduce DC-link capacitor ripple currentSun, Jing 17 September 2007 (has links)
AC/DC adapters mostly employ two-stage topology: Power Factor Correction (PFC) pre-regulation stage followed by an isolated DC/DC converter stage. Low power AC/DC adapters require a small size to be competitive. Among their components, the bulk DC-link capacitor is one of the largest because it should keep the output voltage with low ripple. Also, the size of this capacitor is penalized due to the universal line voltage application. Synchronization through employing leading edge modulation for the first PFC stage and trailing edge modulation for the second DC/DC converter stage can significantly reduce the ripple current and ripple voltage of the DC-link capacitor. Thus, a smaller DC-link capacitance can be used, lowering the cost and size of the AC/DC adapter. Benefits of the synchronous switching scheme were already demonstrated experimentally. However, no mathematical analysis was presented. In this thesis, detailed mathematical analyses in per-unit quantity are given to facilitate the calculation of the DC-link capacitor ripple current reduction with Leading/Trailing Edge Modulation strategies. One of the limitations of leading/trailing edge modulation is that the switching frequencies of the two stages need to be equal to achieve the best reduction of the DC-link capacitor ripple current. The DC-link capacitor ripple current will become larger if the switching frequency of the DC/DC converter is larger than that of the PFC pre-regulator, which blocks us to employ higher frequency for isolated DC/DC converter to reduce its transformer size. This thesis proposed a new Leading/Trailing Edge Modulation strategy to further reduce the DC-link bulk capacitor ripple current when switching frequency of DC/DC converter stage is twice the switching frequency of PFC stage. This proposed pulse width modulation scheme was verified by simulation. Experimental results obtained through digital control based on FPGA are also presented in this thesis.
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Synchronous Voltage Reversal Control of Thyristor Controlled Series CapacitorÄngquist, Lennart January 2002 (has links)
Series compensation of transmission lines is an effectiveand cheap method of improving the power transmission systemperformance. Series capacitors virtually reduces the length ofthe line making it easier to keep all parts of the power systemrunning in synchronism and to maintain a constant voltage levelthroughout the system. In Sweden this technology has been inuse since almost 50 years. The possibility to improve the performance of the ACtransmission system utilizing power electronic equipment hasbeen discussed a lot since about ten years. Some newsemiconductor based concepts have been developed beside thesince long established HVDC and SVC technologies. The ThyristorControlled Series Capacitor (TCSC) is one such concept. Byvarying the inserted reactance an immediate and well-definedimpact on the active power flow in the transmission line isobtained. Several potential applications, specifically poweroscillation damping, benefit from this capability. The conceptimplied the requirement to design a semiconductor valve, whichcan be inserted directly in the high-voltage power circuit.This certainly presented a technical challenge but thestraightforward approach appeared to be a cost-effectivealternative with small losses. It was also realized that the TCSC exhibits quite differentbehaviour with respect to subsynchronous frequency componentsin the line current as compared to the fixed series capacitorbank. This was a very interesting aspect as the risk ofsubsynchronous resonance (SSR), which just involves such linecurrent components, has hampered the use of series compensationin power systems using thermal generating plants. The thesis deals with the modelling and control aspects ofTCSC. A simplifying concept, the equivalent, instantaneousvoltage reversal, is introduced to represent the action of thethyristor controlled inductive branch, which is connected inparallel with the series capacitor bank in the TCSC. The idealvoltage reversal is used in the thesis in order to describe andexplain the TCSC dynamics, to investigate its apparentimpedance at various frequencies, as a platform forsynthesizing the boost control system and as the base elementin deriving a linear, small-signal dynamical model of thethree-phase TCSC. Quantitative Feedback Theory (QFT) then hasbeen applied to the TCSC model in order to tune its boostregulator taking into account the typical variation ofparameters that exists in a power system. The impact of theboost control system with respect to damping of SSR is finallybeing briefly looked at. <b>Keywords:</b>Thyristor Controlled Series Capacitor, TCSC,FACTS, reactive power compensation, boost control, phasorestimation, Quantitative Feedback Theory, subsynchronousresonance, SSR.
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Solution Precursor Plasma Spray Deposition of Super-capacitor Electrode MaterialsGolozar, Mehdi 07 December 2011 (has links)
Double layer capacitors owe their large capacitance to high specific surface area carbon-based electrode materials adhered to a current collector via an adhesive. However, recent studies attribute greater electrical energy storage capacity to transition metal oxides/nitrides: a new generation of electrode materials for use in super-capacitors with mixed double-layer and pseudo-capacitive properties.
Solution precursor plasma spray deposition is a technique that allows coatings to be fabricated with fine grain sizes, high porosity levels, and high surface area; characteristics ideal for application as super-capacitor electrodes. This investigation established conditions for deposition of porous, high specific surface area α-MoO3. It further identified a two-step temperature-programmed reaction for topotactic phase transformation of the α-MoO3 deposits into high specific surface area molybdenum nitrides of higher conductivity and higher electrochemical stability window. The electrochemical behavior of molybdenum oxide/nitride deposits was also studied in order to assess their potential for use in super-capacitors.
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Solution Precursor Plasma Spray Deposition of Super-capacitor Electrode MaterialsGolozar, Mehdi 07 December 2011 (has links)
Double layer capacitors owe their large capacitance to high specific surface area carbon-based electrode materials adhered to a current collector via an adhesive. However, recent studies attribute greater electrical energy storage capacity to transition metal oxides/nitrides: a new generation of electrode materials for use in super-capacitors with mixed double-layer and pseudo-capacitive properties.
Solution precursor plasma spray deposition is a technique that allows coatings to be fabricated with fine grain sizes, high porosity levels, and high surface area; characteristics ideal for application as super-capacitor electrodes. This investigation established conditions for deposition of porous, high specific surface area α-MoO3. It further identified a two-step temperature-programmed reaction for topotactic phase transformation of the α-MoO3 deposits into high specific surface area molybdenum nitrides of higher conductivity and higher electrochemical stability window. The electrochemical behavior of molybdenum oxide/nitride deposits was also studied in order to assess their potential for use in super-capacitors.
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Síntesis de estructuras multiplicadoras de tensión basadas en células convertidoras continua-continua de tipo conmutado.Giral Castillón, Roberto 05 July 1999 (has links)
Uno de los campos más importantes de la Electrónica de Potencia es el de los convertidores de potencia conmutados, que debido a sus características de alto rendimiento energético, reducido tamaño, posibilidades de regulación del factor de potencia y de elevación de tensión, etc., están presentes en un gran número de las etapas de alimentación de los equipos electrónicos actuales.Las mejoras tecnológicas en ámbitos como el de la integración de circuitos han permitido importantes reducciones en el tamaño de los equipos (por ejemplo en los ordenadores). Sin embargo, este proceso de reducción de tamaño que, además, suele venir unido a unas especificaciones más rígidas en cuanto a costes, rendimiento, seguridad y prestaciones en general, no se ha producido en igual medida en las etapas de alimentación. El estudio de los convertidores conmutados es por lo tanto un campo necesitado de esfuerzos de investigación y desarrollo.Para potencias superiores a 25 W, y especialmente en potencias superiores a 150 W, una de las estrategias utilizadas para mejorar las prestaciones de los convertidores es el uso del denominado "interleaving" o entrelazado , definido como la puesta en paralelo de N convertidores idénticos desfasando sus señales de control de forma uniforme a lo largo del periodo de conmutación.Con el objetivo principal de reducir al máximo los rizados de la tensión de salida y de la corriente de entrada, en esta tesis se estudian casos particulares de "interleaving" en estructuras convertidoras continua-continua que utilizan el convertidor elevador ("boost") como célula básica y cuyas tensiones de salida son, idealmente y operando en modo de conducción continua, múltiplos enteros positivos de la tensión de entrada, de ahí la denominación de multiplicadores de tensión que aparece en el título de tesis propuesto. Posteriormente se analizan las posibilidades de regulación de tensión que presentan algunos de los casos de estudio, a costa de incrementar los rizados.
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