13,277 research outputs found
A grid-connected PV/supercapacitor/battery hybrid distributed generation system integrated with multiport DC-DC converter
No full textA <i>hybrid distributed generation system</i> (HDGS) using a <i>multi-input multi-output positive buck-boost converter</i> (MIMO-PBBC) is proposed for the supply-side of the grid-connected <i>photovoltaic</i> (PV) generation power plant, where three PV clusters, one battery bank, and one supercapacitor module are hybridized and regulated by a centralized three-phase dc-ac inverter with their corresponding control systems. The major functionalities of the proposed systems including reactive power control, dc-link voltage regulation, low-voltage ride-through and maximum power point tracking are validated with excellent performance via computational simulation
Towards Agent-oriented Model-Driven Architecture
No full textModel Driven Architecture supports the transformation from reusable models to executable software. Business representations, however, cannot be fully and explicitly represented in such models for direct transformation into running systems. Thus, once business needs change, the language abstractions used by MDA (e.g. Object Constraint Language / Action Semantics), being low level, have to be edited directly. We therefore describe an Agent-oriented Model Driven Architecture (AMDA) that uses a set of business models under continuous maintenance by business people, reflecting the current business needs and being associated with adaptive agents that interpret the captured knowledge to behave dynamically. Three contributions of the AMDA approach are identified: 1) to Agent-oriented Software Engineering, a method of building adaptive Multi-Agent Systems; 2) to MDA, a means of abstracting high level business-oriented models to align executable systems with their requirements at runtime; 3) to distributed systems, the interoperability of disparate components and services via the agent abstraction
High incidence of TEL/AML1 fusion resulting from a cryptic t (12;21) in childhood B-lineage acute lymphoblastic leukemia in Taiwan.
No full textTracking wheel test for DC polymeric insulators
Full text linkIl lavoro di tesi svolto è atto ad apportare delle migliorie nel sistema di trasmissione HVDC (High Voltage Direct Current). Un elemento problematico per le linee aeree HVDC è dato dagli isolatori, questa situazione si aggrava particolarmente nel caso in cui tali linee sono installate in zone altamente inquinate o zone costiere in cui l’aria contiene elevate percentuali di sale. L’inquinamento portato dal vento a depositarsi nella superficie esterna degli isolatori polimerici fa si che si crei uno strato di materiale inquinate che, alla presenza di umidità dovuta a nebbia, brina o pioggerellina leggera, diventa altamente conduttivo e compromette la caratteristica di idrofobia delle superfici dei materiali polimerici.
Test d’invecchiamento si rendono necessari per stimare le performance degli isolatori polimerici con corrente continua in servizio in ambienti inquinati. Il test analizzato ed esposto nella tesi è il test d’invecchiamento che è riportato nella normativa EN 62217:2006 “Polymeric insulators for indoor and outdoor use with a nominal voltage > 1000 V – General definitions, test methods and acceptance criteria” nell’appendice A e definito come “Tracking wheel test”. Con il termine “tracking” la normativa intende specificare quel fenomeno di formazione di percorsi conduttivi (tracks) che causano l’irreversibile degradamento della superficie dell’isolatore. Tali percorsi o tracce conduttive rimangono tali anche quando la superficie è asciutta e per questo investono una grande importanza nel possibile fallimento dell’isolatore.
Il processo di registrazione della corrente di dispersione e le correlazioni con l’invecchiamento dell’isolatore polimerico sono sviluppati nella tes
Common Mode Currents in DC Power Routers
No full textThe grid reinforcement and energy redirection needs have led to the emergence of Back-To-Back Voltage Source Converter (BTB-VSC) based dc power routers. This paper investigates the low frequency Common Mode Currents (CMCs) that arise in the system if the employed BTB-VSCs have an un-isolated ac path connected in parallel to their output ports. Simulation results are presented to show a sensitivity analysis of lower order harmonics in CMC with respect to the operating active and reactive power of the dc router, dc link voltage, link resistance, modulation method and pole capacitance. Experimental results are shared to show existance of lower order CMC in 3-wire ac link operating in parallel with the dc power router and these are mitigated using zero sequence controller
Modeling, Control, and Operation of an M-DAB DC-DC Converter for Interconnection of HVDC Grids
No full textFuture high-voltage direct-current (HVDC) networks based on voltage source converters (VSCs) will have different structures (asymmetric monopolar, bipolar, or symmetric monopolar), voltage levels, control, and protection schemes. Therefore, dc-dc converters are needed to interconnect those VSC-HVDC grids and several technical issues on their control and operational systems must be adequately addressed. A dc-dc converter based on a modular-dual active bridge (M-DAB) converter is suggested to reach a desirable interconnection of the HVDC grids and regulate power flow (PF) between them. A dynamic averaged model is proposed for the M-DAB converter and its stability is analyzed using the Lyapunov function. Moreover, a new local controller based on nonlinear control theory is proposed for the M-DAB. The new M-DAB local controller is integrated with the energy management system (EMS), by updating the PF equations, to create a complete control structure. Considering the CIGRE DCS3 HVDC test system and the studied M-DAB, static, dynamic simulation, and experimental studies are conducted and the dc-dc converter and the performance of the designed controllers and the EMS are examined and validated.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power Grid
Conversores CC-CC não-isolados de alto ganho e de alto rendimento destinados a aplicações fotovoltaicas e baseados no conversor boost com célula de ganho
Full text linkDissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Elétrica, Florianópolis, 2015.Esta dissertação apresenta um estudo sobre conversores cc-cc não-isolados aplicados ao processamento de energia solar fotovoltaica e baseados no conversor Boost. Tais conversores possuem alto rendimento e elevado ganho estático em virtude da utilização de células de ganho, cujo conceito é definido neste trabalho. O princípio de funcionamento dos conversores, as principais formas de onda e os esforços nos componentes são analisados para o modo de condução contínua, independentemente da célula de ganho empregada. Uma metodologia para criação das células de ganho é desenvolvida, bem como uma breve extensão desse conceito. O estudo realizado é avaliado em dois protótipos: o primeiro é desenvolvido apenas para comparar os ganhos de tensão teórico e experimental de diferentes células de ganho; enquanto o segundo é construído a partir de um algoritmo de otimização desenvolvido para maximizar o rendimento de um conversor de 200 W, integrado a um módulo fotovoltaico. Ademais, uma nova e eficiente técnica de rastreamento de máxima potência é implementada em conjunto com o conversor otimizado.Abstract : This work presents a study on non-isolated dc-dc converters applied to photovoltaic solar energy processing based on the conventional Boost converter. Such converters demonstrate high efficiency and high step-up gain due to the usage of gain cells, whose concept is defined in this work. The operating principle, the key waveforms and the components stresses are analyzed for continuous conduction mode independently of the employed gain cell. A methodology to create the gain cells is developed, as well as a brief extension of this concept. The conducted study is evaluated in two prototypes: the first is just developed for the comparison of theoretical and experimental voltage static gain of different gain cells; while the second is dimensioned by an optimization algorithm developed to maximize the efficiency of a 200 W photovoltaic module integrated converter. Moreover, a new and efficient maximum power tracking method is implemented together with the optimized converter
Restructuring the existing medium voltage distribution grids using DC systems
No full textGreen Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.DC systems, Energy conversion & Storag
Cold cracking in DC-cast high strength aluminum alloy ingots: An intrinsic problem intensified by casting process parameters
Full text linkFor almost half a century the catastrophic failure of direct chill (DC) cast high strength aluminum alloys has been challenging the production of sound ingots. To overcome this problem, a criterion is required that can assist the researchers in predicting the critical conditions which facilitate the catastrophic failure of the ingots. This could be achieved at first glance by application of computer simulations to assess the level and distribution of residual thermal stresses. However, the simulation results are only able to show the critical locations and conditions where and when high stresses may appear in the ingots. The prediction of critical void/crack size requires simultaneous application of fracture mechanics. In this paper, we present the thermo-mechanical simulation results that indicate the critical crack size distribution in several DC-cast billets cast at various casting conditions. The simulation results were validated upon experimental DC-casting trials and revealed that the existence of voids/cracks with a considerable size is required for cold cracking to occur.Materials Science & EngineeringMechanical, Maritime and Materials Engineerin
A Dynamically Reconfigurable Recursive Switched-Capacitor DC-DC Converter with Adaptive Load Ability Enhancement
No full textMultiple voltage conversion ratio (VCR) recursive switched-capacitor (SC) dc-dc converters, based on several basic 2:1 converters, are widely used for on-chip power supplies due to their flexible VCRs for higher energy efficiency. However, conventional multiple VCR SC converters usually have one or more 2:1 converters unused for some VCRs, which results in lower power density and chip area wastage. This article presents a new recursive dc-dc converter system, which can dynamically reconfigure the connection of all on-chip 2:1 converter cells so that the unused converters in the conventional designs can be reused in this new architecture for increasing the load-driving capacity, power density, and power efficiency. To validate the design, a 4-bit-input 15-ratio system was designed and fabricated in a 180-nm BCD process, which can support a maximum load current of \text{0.71}\,\text{mA} and achieves a peak power efficiency of 93.1% with 105.3\,\mu \text{A/mm} {2} chip power density from a 2-V input power supply. The measurement results show that the load-driving capacity can become 6.826×, 2.236×, and 2.175× larger than the conventional topology when the VCR is 1/2, 1/4, and 3/4, respectively. In addition, the power efficiency under these specific VCRs can also be improved considerably.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Electronic Instrumentatio
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