901 research outputs found

    A review of recent control techniques of drooped inverter‐based AC microgrids

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    As the penetration of distributed generation (DG) systems in the grid is increasing, the challenge of combining large numbers of DGs in the power systems has to be carefully clarified and managed. The control strategy and management concept of the interconnected systems should be flexible and reliable to handle the various types of DGs. This can be suitably met by microgrids. This paper introduces the microgrid structure and elements and states the main objectives that should be achieved by the microgrid controllers and each DG controller in both operation modes (grid-connected and island mode). It also presents the challenges of having multiple DG units in a microgrid in terms of accurate power control/sharing, voltage and frequency regulation, power management between DGs, different renewable energy sources integration and deployment, seamless mode transfer, and the modeling issues. The centralized and decentralized control techniques as potential solutions have been discussed and compared by highlighting the advantages and disadvantages of each. Furthermore, the recent control techniques for drooped alternating current microgrids and the main proposed solutions and contributions in the literature have been exposed to finally overcome the droop control limitations and obtain a flexible and smart distributed power system

    Machine learning in solar physics

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    The application of machine learning in solar physics has the potential to greatly enhance our understanding of the complex processes that take place in the atmosphere of the Sun. By using techniques such as deep learning, we are now in the position to analyze large amounts of data from solar observations and identify patterns and trends that may not have been apparent using traditional methods. This can help us improve our understanding of explosive events like solar flares, which can have a strong effect on the Earth environment. Predicting hazardous events on Earth becomes crucial for our technological society. Machine learning can also improve our understanding of the inner workings of the sun itself by allowing us to go deeper into the data and to propose more complex models to explain them. Additionally, the use of machine learning can help to automate the analysis of solar data, reducing the need for manual labor and increasing the efficiency of research in this field.Comment: 100 pages, 13 figures, 286 references, accepted for publication as a Living Review in Solar Physics (LRSP

    Investigation Of Metal Modulated Epitaxy Grown III-Nitride High-Power Electronic And Optoelectronic Devices

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    The wide-bandgap material GaN (Eg = 3.4 eV) continues to mature due to its achievements in high-power electronic and optoelectronic devices. The fully vertical GaN high-power devices show high performance but are very expensive. Quasi-vertical GaN devices are cost-effective but lack high performance due to low quality films. Improvement in the performance of quasi-vertical devices would make this technology suitable for high volume production. Although the market of GaN based devices is still growing, significantly higher performance parameters can potentially be achieved with the ultrawide-bandgap semiconductor material AlN with the bandgap as high as 6.1 eV. The only limitation to AlN-based devices so far was doping. An extensive study is performed to explore the 3D phase diagram of MME to find the optimized morphological, electrical, structural, and optical growth conditions to achieve high performance high-power quasi-vertical GaN pin diodes. Thick abrupt Beryllium step-doped GaN i-layers were used to demonstrate these high-power devices. Novel fabrication methods and current spreading layers are introduced in these devices. Furthermore, for the first time in more than 8 decades of AlN research, substantial bulk conduction, both p-type and n-type, was achieved in MME AlN and the first known p-n junction AlN diodes are demonstrated to extend the high-power performance of nitride technology. Also, MME mixed AlN/GaN Pin and junction barrier Schottky diodes are demonstrated to achieve low turn-on voltage and higher breakdown performance simultaneously. The conductive AlN films show great promise for AlN-based device applications that could potentially revolutionize deep ultraviolet light based viral and bacterial sterilization, polymer curing, high-temperature, high-voltage and high-power electronics among many societal impacts.Ph.D

    Sliding mode approach for control and observation of a three phase AC-DC pulse-width modulation rectifier

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    Introduction. For AC-DC conversion systems, the electrical systems typically use thyristor or diode bridge rectifiers, which have relatively poor performance. Nowadays, three-phase pulse-width modulation rectifiers are widely applied in various applications for their well-known intrinsic benefits, such as adjustable DC link voltage, unity power factor, bidirectional power flow and very low total harmonic distortion. Purpose. The objective of this work is to achieve better stability and dynamic performance using sliding mode strategy for control and observation. Methods. For that purpose, first a sliding mode controller is introduced on the DC-link side to ensure a fast and accurate response of the output load voltage. Then, the sliding mode approach is employed to control the quadrature and direct components of power to maintain the input power factor at unity. Finally, this approach is used to design two observers for grid voltage estimation and online variation of load resistance. To overcome the problem associated with the use of the classical low-pass filter, an adaptive compensation algorithm is used to compensate the attenuation of the amplitude and phase delay of the observed grid voltages. This algorithm is based on the use of the two low-pass filters in cascade and ensures the minimization of chattering. Results. Comparative studies have been carried out between sliding mode control method for controlling the three-phase AC-DC pulse-width modulation rectifier and other conventional techniques. The validation by simulation and the tests carried out gave very satisfactory results and proved the effectiveness and feasibility of the sliding mode for both control and observation of three phase pulse-width modulation rectifier.Вступ. Для AC-DC систем перетворення електричні системи зазвичай використовують тиристорні або діодні мостові випрямлячі, які мають відносно погані характеристики. В даний час трифазні випрямлячі з широтно-імпульсною модуляцією широко застосовуються з різними цілями завдяки їх добре відомим внутрішнім перевагам, таким як регульована напруга у ланці постійного струму, одиничний коефіцієнт потужності, двонаправлений потік потужності та дуже низькі загальні гармонічні спотворення. Метою даної роботи є досягнення кращої стабільності та динамічних характеристик з використанням стратегії ковзного режиму для контролю та спостереження. Методи. З цією метою спочатку на стороні ланки постійного струму вводиться регулятор режиму ковзання, щоб забезпечити швидку і точну реакцію на вихідну напругу навантаження. Потім використовується метод ковзного режиму для управління квадратурною та прямою складовими потужності, щоб підтримувати вхідний коефіцієнт потужності рівним одиниці. Нарешті цей підхід використовується для розробки двох спостерігачів для оцінки напруги мережі та зміни опору навантаження в режимі онлайн. Для подолання проблеми, пов'язаної з використанням класичного низькочастотного фільтру, використовується алгоритм адаптивної компенсації, що компенсує загасання амплітуди і фазової затримки напруг мережі, що спостерігаються. Цей алгоритм заснований на використанні двох низькочастотних фільтрів у каскаді та забезпечує мінімізацію брязкоту. Результати. Були проведені порівняльні дослідження між методом керування ковзним режимом для керування трифазним випрямлячем AC-DC з широтно-імпульсною модуляцією та іншими традиційними методами. Перевірка за допомогою моделювання та проведені випробування дали дуже задовільні результати та довели ефективність та здійсненність ковзного режиму як для управління, так і для спостереження за трифазним випрямлячем з широтно-імпульсною модуляцією

    Pathways towards single-polariton nonlinearity : from ground state exciton-polariton condensates in GaAs to Rydberg exciton-polaritons in Cu₂O

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    This work explores several routes towards achieving single-polariton nonlinearity. Exciton-polaritons are part-light part-matter quasiparticles arising from the strong coupling of excitons and cavity photons in micron-sized optical cavities. Owing to their excitonic component, polaritons can be described as "dressed photons" with nonlinear interactions several orders of magnitude larger than in typical optical materials. However, interactions between microcavity polaritons have remained weak, with the single-polariton nonlinearity being much smaller than the cavity linewidth. In this thesis, two approaches are studied as a way of circumventing this limitation and entering the nonlinear regime. The first approach involves narrowing the emission linewidth of a polariton condensate through optical confinement so that the linewidth approaches the interaction constant. The second approach involves exploiting the giant nonlinearities of Rydberg excitons in cuprous oxide, first in nanoparticles to study the effect of quantum confinement and then inside a microcavity to create highly nonlinear Rydberg exciton-polaritons. The main result presented in this thesis are: (1) An optically trapped polariton condensate in a state-of-the-art GaAs-based microcavity approaches but still remains away from the regime of single-polariton nonlinearity. The condensate is characterised by an ultra-narrow linewidth as evidenced by the temporal decay of its coherence. The latter also exhibits an oscillatory behaviour originating from a beating between two condensate modes. (2) Rydberg excitons states are resolved up to principal quantum number n = 6 in the absorption spectrum of clusters of cuprous oxide nanoparticles. Rydberg excitons are also resolved for single nanoparticles; however, the spectrum is dominated by effects inherent to the nanoparticle system, thus hindering the study of the nonlinearity of Rydberg excitons in this quantum-confined structure. (3) Strong coupling between cavity photons and Rydberg excitons can be achieved by embedding a thin cuprous oxide crystal as the active layer of an optical microcavity. Even though the microcavity is below the nonlinear regime for all strongly coupled Rydberg states, non-classical light can be observed by reducing the mode volume and suppressing the phonon-background of cuprous oxide in future microcavities. This thesis is a major step towards realising single-polariton nonlinearity for future quantum applications. The results presented in this work highlight the limitations of traditional GaAs-based semiconductor microcavities while establishing Rydberg polaritons with their huge nonlinearities as a promising route for achieving a scalable, strongly correlated photonic platform

    Emerging Power Electronics Technologies for Sustainable Energy Conversion

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    This Special Issue summarizes, in a single reference, timely emerging topics related to power electronics for sustainable energy conversion. Furthermore, at the same time, it provides the reader with valuable information related to open research opportunity niches

    Enhancement of fault current contribution from inverter-based resources

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    The reduction in levels of fault current infeed as inverter-based resources (IBR) displace synchronous machines undermines the ability of a conventional protection system to identify and isolate faults in an effective manner and is therefore a concern for system operators (SOs). This observation provided the motivation to investigate the limitations of IBRs when injecting fault current and to explore how these limitations might be overcome. This thesis investigates techniques aimed at significantly increasing Fault Current Contribution (FCC) from an IBR system so that renewable energy resources can continue to be deployed without compromising the protection system. The techniques for enhancing FCC are at three different levels of an IBR system: at semiconductor or device level, circuit level and system level. The first study uses phase change materials (PCM) to provide a short-term overload rating to insulated-gate bipolar transistors (IGBTs) and found them to have very limited potential to provide FCC. A Finite Element Analysis (FEA) of heat-flow concluded that, although the PCM was useful for dealing with short over-load currents, it was unsuitable for facilitating large fault currents of several times normal load current. The view was that if the fault current cannot be created at device level through better thermal management, then a circuit level innovation would be required. The second study investigates series/parallel switching of submodules in modular converters. This takes advantage of the fact that during a fault, the line voltage is reduced, and if it falls below 0.5 pu then half of the sub-modules (SMs) can be put into parallel with the other half to double the FCC (2 pu) at half the voltage (0.5 pu). Similarly, if the voltage drops below 0.25 pu, parallel connection of four groups of SMs would enable 4 pu current capability. A model of a static synchronous compensator (STATCOM) was developed, inspired by the alternate arm converter (AAC), with the director switch of the AAC used as part of the reconfiguration circuit. The conclusion of this study was that the penalty paid in power losses in the additional semiconductor devices used for reconfiguration is reasonable for the 2 pu FCC case but not at the 4 pu FCC case. The third study was based on circuit reconfiguration but beyond the converter itself and in this case the windings of the coupling transformer of a STATCOM. Sections of winding were switched using thyristors to tap-change the transformer by a large factor. Using the proposed thyristor-based electronic tap-changer (eTC), the number of turns of the grid-side winding was reduced during a voltage dip, so that larger current can be delivered to the network for the same converter current. The STATCOM was controlled in the natural frame (abc frame) and this control is used to actively drive the currents in the tap-changer thyristors to zero when needed so that they can be commuted rapidly. The transformer was configured to give a normal ratio of 1:4 and be able to tap-down to 1:2 and 1:1 to increase FCC to 2 pu or 4 pu. Theoretical analysis of, and operating principles for, the proposed eTC, together with their associated control schemes, are verified by time-domain simulation at full-scale. The case-study circuit demonstrates delivery of substantial fault current contribution (FCC) of up to 4 pu at the point of common coupling (PCC) in less than half a cycle (10 ms) after detection of three- and single-phase faults. The results demonstrate that the proposed eTC is a good candidate for the enhancement of fault current from IBR systems that employ coupling transformers, allowing them thereby to make a contribution to future electricity networks dominated by IBR.Open Acces

    Jets in hot nuclear matter : Resumming multiple emissions in QCD

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    Under tung-ion-kollisjonar med høg energi smeltar protonar og nøytronar saman og dannar eit kvark-gluon-plasma. Modifiseringa av jeter, som forplantar seg gjennom det avgrensa mediet, har vorte grundig forska på ved CERN-LHC, og BNL-RHIC i kollisjonseksperiment. I løpet av det siste tiåret har man samla opp omfattande kunnskap om teorien om jet-modifikasjonar. Denne avhandlinga presenterer eit konsistent og toppmoderne perspektiv på jet-modifikasjonar basert på perturbasjons-QCD. Tatt i betraktning nylege framsteg mot ei meir nøyaktig forklaring av jeter i høgenergifysikk, vert jet-modifikasjonar i mediet gjennomgått ved å fokusera på deira perturbasjonsstruktur i alle orden og definere grannsemda til observerbare jet-strålar.In high-energy heavy-ion collisions, protons and neutrons melt and form the quark-gluon plasma. The modification of jets, propagating through this deconfined medium, has been extensively studied at the CERN-LHC, and the BNL-RHIC colliders experiments. Over the last decade, extensive knowledge has piled up in the theory of jet modification. This thesis presents a consistent and state-of-the-art perspective of jet modification based on perturbative QCD. Considering recent progress toward a more accurate description of jets in high-energy physics, jet modification in the medium is reviewed by focusing on their all-order perturbative structure and defining the accuracy of quenched jet observables.Doktorgradsavhandlin

    National Conference on ‘Renewable Energy, Smart Grid and Telecommunication-2023

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    Theme of the Conference: “The challenges and opportunities of integrating renewable energy into the grid” The National Conference on Renewable Energy, Smart Grid, and Telecommunication - 2023 is a platform for industry experts, researchers, and policymakers to come together and explore the latest advancements and challenges in the fields of renewable energy, smart grids, and telecommunication. Conference Highlights: In-depth discussions on renewable energy technologies and innovations. Smart grid integration for a sustainable future. The role of telecommunication in advancing renewable energy solutions. Networking opportunities with industry leaders and experts. Presentation of cutting-edge research papers and case studies. Conference topics: Renewable Energy Technologies and Innovations Smart Grid Development and Implementation Telecommunication for Energy Systems Energy Storage and Grid Balancing Policy, Regulation, and Market Dynamics Environmental and Social Impacts of Renewable Energy Energy Transition and Future Outlook Integration of renewable energy into the grid Microgrids and decentralized energy systems Grid cybersecurity and data analytics IoT and sensor technologies for energy monitoring Data management and analytics in energy sector Battery storage technologies and applicationshttps://www.interscience.in/conf_proc_volumes/1087/thumbnail.jp
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