1,107 research outputs found

    High Voltage DC-biased Oil Type Medium Frequency Transformer; A Green Solution for Series DC Wind Park Concept

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    The electric energy generated by remote offshore wind parks is transported to the consumers using high voltage submarine cables. On the generation site, such transmissions are realized today by collecting the energy produced by several wind turbines in a bulky and expensive transformer placed on a dedicated platform. An alternative solution has been proposed recently, which allows to reduce the installation and maintenance costs by eliminating such a platform. It is suggested to equip each wind turbine in the wind park by an individual DC/DC converter and connect them in series to reach the DC voltage level required for an efficient HVDC energy transportation to the shore. The DC/DC converter is supposed to be a Dual Active Bridge (DAB) converter, which can be made reasonably small to be placed on the wind turbine tower or even in its nacelle. The key element of the converter defining its size and mass is a special transformer, which operates at voltages comprising a high (switching) frequency component superimposed on a high DC offset voltage. DC insulation design of such a transformer and investigation of the effects of a high DC insulation level on the other electromagnetic properties of the transformer is the subject of the present research.In order to verify the concept a prototype of the transformer was built, and its evaluation presented. The unit has been manufactured for the rated power of 50 kW and rated voltages 0.4/5 kV including DC offset of 125 kV and square-shaped oscillations with the frequency of 5 kHz. The magnetic system was made of ferrite material and consisted of 10 shell-type core segments. The magnetic properties have been verified by measuring magnetization and losses at various frequencies in the range 1-10 kHz to cover the operational range of the DAB. The types and dimensions of the windings and their conductors were chosen to minimize the proximity and eddy current effects at higher frequencies. To reduce the size of the transformer and to allow for its efficient cooling, the active part was immersed in oil and cellulose-based materials (paper and pressboard) were used to build the high voltage insulation system. The principles for dimensioning the insulation of the transformer are discussed. The criteria used for selecting insulating distances were based on the consideration of the electric field strength obtained from FEM simulations and using the non-linear Maxwell-Wagner model accounting for local variations of the electric field caused by accumulation of interfacial charges induced by DC stresses. The properties of the materials needed for the calculations were obtained by measuring their dielectric constants and electric conductivities. The methodology used for the measurements conducted for conventional mineral oil and eco-friendly biodegradable transformer oils and, respectively, for oil-impregnated paper/pressboard, is presented. The methodologies used for obtaining parameters of the built transformer prototype needed for its integration in the power electric circuit of the DAB are introduced. A method developed for accurate calculations of the leakage inductance for the shell-type multi core transformers with circular windings is described. Two innovative methods for evaluations of parasitic capacitances based on high frequency equivalent circuits of the transformer are presented. The results of their verifications against performed Frequency Response Analysis measurements and FEM calculations as well as their accuracy are discussed.Thermal performance of the developed transformer prototype is analysed based on the results of computer simulations of heat transfer in its active part under rated load. Identified hot spots and solutions for their elimination are presented.Finally, the expected dimensions, weight, and efficiency of an actual DC/DC converter with the rated parameters corresponding to a 6 MW, 1.8 kV real wind turbine having a 250 kV offset DC voltage are estimated assuming that the developed transformer prototype is scalable. It is shown that the proposed solution allows for installing the full-scale converter having 2.2 Tons in weight and 1.8 m3 in volume on the bottom of the wind turbine’s tower

    Auxiliary Resonant Commutated Pole Inverter (ARCPI) with SiC MOSFETs for efficient Vehicle-to-Grid (V2G) charging

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    The need for energy storages is growing with an increasing share of renewable energy sources in the electricity grid. The roll-out of electric vehicles into the mass market will bring huge battery storage capacities into the grid, which have remained largely unused so far but could be used to temporarily store energy. One key enabler for this is low-cost, efficient and compact power electronics, like the Auxiliary Resonant Commutated Pole Inverter (ARCPI), which is a promising topology for bidirectional AC/DC converters in battery chargers. In this paper, we present the principle of operation and a simulation of the ARCPI. In addition, we provide first results from an ARCPI prototype using SiC MOSFETs designed for a power of up 22 kW, DC link voltages of up to 920 V and peak efficiencies beyond 99 %

    Medium Voltage Solid-State Transformer:An IEC60076-3 based design

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    A novel high-voltage gain step-up DC–DC converter with maximum power point tracker for solar photovoltaic systems

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    In order to generate electricity from solar PV modules, this study proposed a novel high-voltage gain step-up (HVGSU) DC–DC converter for solar photovoltaic system operation with a maximum power point (MPP) tracker. The PV array can supply power to the load via a DC–DC converter, increasing the output voltage. Due to the stochastic nature of solar energy, PV arrays must use the MPPT control approach to function at the MPP. This study suggests a novel HVGSU converter that uses the primary boost conversion cell and combines switched capacitors and voltage multiplier cells. The proposed topology is upgradeable for high-voltage gain step-up and can be incorporated as well. A clamp circuit reuses the energy that leaks out so that the switch voltage stress and power loss are kept to a minimum. One thing that makes it stand out is that the voltage stress on the diodes and switch stays low and constant even as the duty cycle changes. Additionally, the inductor greatly reduces the diodes’ reverse recovery losses. There is a lot of information about steady-state analyses, operation principles, and design guidelines. A prototype circuit is built to test the maximum power point tracking operation with voltage conversion from 20–40 V to 380 V at 150 W. The results of the experiments support the theoretical analysis and claimed benefits. The proposed converter has the ability to track the maximum power point and a high conversion efficiency over a wide range of power. A weighted efficiency of 90–96% is shown by the prototype

    A Current-Source Modular Converter for Large-Scale Photovoltaic Systems

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    The world is shifting toward renewable energy sources (RESs) to generate clean energy and mitigate the stress of global warming caused by CO2 emissions in recent decades. Among several RES types, large-scale photovoltaic (LSPV) plants are a promising source for meeting ambitious clean energy targets and being part of power generation. With the progress of high-power modular inverters, new opportunities have arisen to integrate them into LSPV systems connected to medium-voltage (MV) grids to obtain high efficiency and reliability, better system flexibility, and improved electrical safety compared with string or central inverters. This thesis presents and implements a new current source three-phase modular inverter (TPMI) based on a novel dual-isolated SEPIC/CUK (DISC) converter. The TPMI is designed with a single power processing stage comprised of seriesconnected DISC submodules (SMs) to deliver MV into the utility grid. It outperforms conventional high-power inverters in terms of modularity, scalability, galvanic isolation compliance, and distributed maximum power point tracking (MPPT) capabilities. The DISC converter employed as an SM in the proposed TPMI generates bipolar output (i.e., both positive and negative voltages). In addition to having step-up and step-down capabilities with a continuous input current, this converter shares an input side inductor, thereby reducing the number of components. The DISC structure, modulation method, operation, novel state-space model, and parameter design procedure are analysed in details. Then, simulation results are presented to validate the theoretical and analytical analyses of the DISC converter. The proposed TPMI inverter is subsequently integrated into the LSPV grid connection to prove its suitability for such applications. In the theoretical analysis, the advantages of TPMI structure over conventional topologies are discussed. Then, the modulation technique, and operational concept are presented, followed by a dedicated control strategy is implemented by adding a system and SM-level controllers. The system controller is required for the generation of uniform duty ratios for all SMs in order to regulate the power transfer. The SM level controller is introduced to ensure equal current and voltage distribution between SMs and to compensate for minor discrepancies between the various parameters. The entire TPMI system is demonstrated through MATLAB and Simulink simulations, with the objective being to deliver the rated (1 MW) power from the PV modules under normal operation, uniform shading, and partial shading conditions and to match PV generation with the grid’s power demands. A downscaled 3-kW TPMI inverter was developed in the laboratory to validate its feasibility experimentally with its control strategy in different operating conditions. Finally, the TPMI performance is compared with selected current source inverter topologies, which shows that TPMI obtains good efficiency within the context of existing state-of-the-art current source converters. Then, the TPMI structure is modified by redesigning its DISC SMs, which provides several benefits, including a reduction in the number of switch devices operating at high frequency, thus decreasing switching losses, and an increase in efficiency. In this study, a half-cycle modulation (HCM) scheme is developed for the switches, and the operation of a modified DISC SM is analysed. Simulation and experimental results validate the performance of the modified TPMI topology and demonstrate its suitability for LSPV applications. According to the results of the comparison, the maximum power efficiency of the modified TPMI structure is 95.5%, which represents an improvement over the original TPMI structure

    Magnetic Integration Techniques for Resonant Converters

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    This thesis sets out a series of new transformer topologies for magnetic integration in different resonant converters. Resonant converters like LLC converters require a high number of magnetic components, leading to low power density and high cost. These magnetic components can usually be integrated into a single transformer to increase power density, efficiency, manufacturing simplicity and to reduce cost. This strategy is known as integrated transformer (IT). The work described in this thesis has sought to deliver improvements in implementing this strategy. The benefits of resonant converters compared to pulse-width-modulated (PWM) converters are discussed. To show the drawbacks of PWM converters, two hard-switched DC-DC converters and two soft-switched DC-DC converters using state-of-the-art wide bandgap (WBG) gallium nitride devices are constructed and investigated. The LLC resonant converter is fully discussed for unidirectional and bidirectional applications. The different techniques for magnetic integration that can be applied to the LLC resonant converter are reviewed. Amongst these techniques, the inserted-shunt integrated transformers, which have gained popularity recently, are made a focus of the thesis. In general, the important challenges concerning the inserted-shunt integrated transformers are the need for bespoke material for the shunt, unwanted high leakage inductance on the secondary side, and that integrated magnetics are not usually suitable for bidirectional converters such as CLLLC converters. Two new topologies (IT1 and IT2) for inserted-shunt integrated transformers are presented that do not need bespoke material for the shunt and can be constructed from materials available commercially in large and small quantities. However, the manufacturing of these proposed topologies is challenging since magnetic shunts are made by joining several smaller magnetic pieces to form a segmented piece. A further new topology (IT3) is presented that not only does not need bespoke material for the shunt but also benefits from simple manufacturing. However, inserted-shunt integrated transformer, including all three proposed topologies (IT1-IT3), still suffer from increased leakage inductance on the secondary side, leading the control and design of the resonant converters to difficulty. Another topology (IT4) is therefore proposed that can be constructed easily with commercially available materials and does not increase the leakage inductance on the secondary side. However, all four proposed topologies (IT1-IT4) and other topologies with an inserted-shunt are not suitable for use in bidirectional LLC-type resonant converters when different primary and secondary leakage inductances are needed, such as where variable gain is required. Finally, a topology (IT5) is proposed that can be used in bidirectional LLC-type converters while it still benefits from simple manufacturing and using commercially available materials. All the proposed topologies (IT1-IT5) are discussed in detail and their design guidelines and modelling are provided. The theoretical analysis is confirmed by finite-element (FEM) analysis and experimental results. A unidirectional LLC resonant converter and a bidirectional CLLLC resonant converter are implemented to investigate the performance of the proposed integrated transformers (IT1-IT5) in practice. It is shown that the converters can operate properly while all their magnetic components are integrated into the proposed transformers

    Desenvolvimento de carregador rápido para veículos elétricos

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    The increase in the combustion of fossil fuels to meet the growing demand for energy is one of the main causes for the increase in the concentration of carbon dioxide (CO2) in the atmosphere. In an attempt to slow this growing environmental pollution, the vast majority of the world’s nations have committed to reduce emissions of CO2 and other greenhouse gases. With this in mind, the transition from combustion vehicles to electric vehicles (EVs) is seen by many authors as one of the most promising developments for reducing greenhouse gas emissions and improving air quality. However, the biggest obstacle to the popularization of this type of vehicle is the time needed to recharge its batteries, during a trip for example. Having said all these paradigms, this dissertation presents the development of a three-phase fast charger for electric vehicle batteries. Nominally this charger is designed to deliver up to 50 [kW] and 100 [A] nominal to the battery. The first charging stage consists of an AC/DC converter coupled to an LCL filter and connected to the power grid at 220 [V] Phase-Phase. The second stage consists of a DC/DC interleaved converter, which is connected to the DC bus at 500 [V]. The charger is coupled to the battery in order to validate charging through the CC-CV method (Constant Current - Constant Voltage). The operation of the converter and its control technique are validated through simulations in the Matlab software, using the Simulink tool. Then, the charger is built using the AC/DC first stage and its operation is demonstrated using a bank of batteries. The control strategy is implemented in the DSP TMS320F28379D from Texas Instruments, using the software Code Composer. Satisfactory results were obtained in the battery charging control although the practical implementation is done on a small scale, the control system can be easily used at higher powers, just with adjustments in the control gains. The importance of compensating the dead-times that appear in the practical part is highlighted.O aumento da combustão de combustíveis fósseis para atender à crescente demanda de energia é uma das principais causas para o aumento da concentração de dióxido de carbono (CO2) na atmosfera. Em uma tentativa de frear esta crescente poluição ambiental, a grande maioria das nações mundiais se comprometeu a reduzir as emissões de CO2 e outros gases de efeito estufa. Tendo isto em vista, a transição dos veículos a combustão para os elétricos (EVs) é vista por muitos autores como uma das evoluções mais promissoras para se reduzir as emissões de gases de efeito estufa e melhorar a qualidade do ar. No entanto o grande empecilho para a popularização deste tipo de veículo é o tempo necessário para recarregar suas baterias, durante uma viagem por exemplo. Dito todos estes paradigmas, esta dissertação apresenta o desenvolvimento de um carregador rápido trifásico para bateria de veículos elétricos. Nominalmente este carregador é projetado para fornecer até 50 [kW] e 100 [A] nominal para a bateria. O primeiro estágio de carregamento consiste em um conversor CA/CC acoplado a um filtro LCL e conectado à rede elétrica em 220 [V] Fase-Fase. O segundo estágio é composto por um conversor CC/CC interleaved, este é conectado ao barramento CC em 500 [V]. O carregador é acoplado à bateria afim de validar o carregamento por meio do método de CC-CV (Corrente Constante - Tensão Constante). A operação do conversor e sua técnica de controle são validadas por meio de simulações no software Matlab, por meio da ferramenta Simulink. Em seguida, o carregador é construído utilizando o primeiro estágio CA/CC e seu funcionamento é demonstrado utilizando um banco de baterias. A estratégia de controle é implementada no DSP TMS320F28379D da Texas Instruments, por meio do software Code Composer. Foram obtidos resultados satisfatórios no controle de carregamento das baterias e, apesar de a implementação prática ser feita em escala reduzida, o sistema de controle pode ser facilmente utilizado em potências maiores, apenas com ajustes nos ganhos do controle. Destaca-se a importância de compensação dos dead-times que aparecem na parte prática

    Design of a 350 kW DC/DC Converter in 1200-V SiC Module Technology for Automotive Component Testing

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    In this paper, the design and implementation of a DC/DC converter for automotive component testing with state-of-the art performance is described. The converter is the core of a battery emulator for the characterization and development of automotive batteries, electronic chargers, traction inverters, DC-DC converters, E-motors and E-axles. Cutting edge performance, flexibility and compactness are obtained by exploiting 1200-V SiC modules, high switching frequency, planar transformer technology, suitable topology solutions and fast digital control strategies. The implemented system is a liquid-cooled, bidirectional converter with galvanic isolation capable of 350 kW continuous output power, output voltage range 48-1000 V, continuous output current up to 800 A (1600 A peak), voltage/current ramp-up time below 10/2 ms and 0.1% current/voltage accuracy. The entire instrument is implemented in a standard full-height 19-inch rack cabinet

    Desarrollo de un control PID para un sistema de almacenamiento de energía basado en supercapacitores mediante un Convertidor Dual Active Bridge (DAB).

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    This work focuses on the simulation of a double active bridge (DAB) converter applying a proportional, integral and derivative (PID) control strategy in open loop and closed loop during the charging and discharging process of the power system based on supercapacitors, controlling the voltage output when the converter works in a steady state to maintain a constant power transfer over a time interval.Este trabajo se centra en la simulación de un convertidor de doble puente activo (DAB) aplicando una estrategia de control proporcional, integral y derivativo (PID) en lazo abierto y en lazo cerrado durante el proceso de carga y descarga del sistema de potencia basado en supercondensadores, controlando la salida de tensión cuando el convertidor trabaja en estado estacionario para mantener una transferencia de potencia constante durante un intervalo de tiempo

    A Three-Port DC/DC Converter (TPC) for Small-Scale Standalone PV-Battery Systems

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    While conventional electricity generation relies on fossil fuels like coal, oil, and gas, renewable energy relies on abundant sources like sunlight, wind, water, and geothermal heat, offering eco-friendly alternatives with minimal emissions. Unlike conventional electricity generation, renewable sources reduce our carbon footprint, aid in combating climate change, and provide lasting energy security. Due to their intermittent nature, implementing energy storage and smart grid technologies becomes essential to maintain a stable electricity supply. Off-grid communities face challenges in accessing reliable energy due to lack of connection to centralized grids. Therefore, renewable energy sources, such as solar, wind, and other sources can help these communities establish self-sustaining, clean, and cost-effective power solutions. Despite the impressive advancements in renewable energy technologies, a significant global population still lacks access to basic energy. According to the United Nations, their ambitious objective is achieving universal energy access, aiming for 100% global coverage by 2030. Therefore, this thesis provides a solution for off-grid communities who lack energy access. It proposes a novel design of a three-port DC/DC Converter (TPC) for small-scale standalone PV-Battery applications. The derivation process of the topology and the optimization methodology are comprehensively explained. Moreover, the modes of operation are elaborated to demonstrate the functionality of the TPC. Furthermore, the controlling method to regulate the output voltage, control the battery current, and track the maximum power point (MPP) of the PV source is discussed. The performance of the proposed topology is validated using PSIM software. A comprehensive simulation analysis is conducted for a load profile of an induvial household in Zimbabwe over a 24-hour period. The steady-state waveforms for all the modes and the mode transition waveforms are all presented and discussed. Additionally, the efficiency for the proposed design is calculated for different range of loads and compared with other topologies. Finally, two case studies are given to observe and analyze the system's response to different scenarios during the 24-hour period
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