Grid converters are the key player in renewable energy integration. The high penetration of renewable energy systems is calling for new more stringent grid requirements. As a consequence, the grid ...converters should be able to exhibit advanced functions like: dynamic control of active and reactive power, operation within a wide range of voltage and frequency, voltage ride-through capability, reactive current injection during faults, grid services support.This book explains the topologies, modulation and control of grid converters for both photovoltaic and wind power applications. In addition to power electronics, this book focuses on the specific applications in photovoltaic wind power systems where grid condition is an essential factor.With a review of the most recent grid requirements for photovoltaic and wind power systems, the book discusses these other relevant issues:modern grid inverter topologies for photovoltaic and wind turbines islanding detection methods for photovoltaic systems synchronization techniques based on second order generalized integrators (SOGI) advanced synchronization techniques with robust operation under grid unbalance condition grid filter design and active damping techniques power control under grid fault conditions, considering both positive and negative sequences Grid Converters for Photovoltaic and Wind Power Systemsis intended as a coursebook for graduated students with a background in electrical engineering and also for professionals in the evolving renewable energy industry. For people from academia interested in adopting the course, a set of slides is available for download from the website. www.wiley.com/go/grid_converters
Control of Power Converters in AC Microgrids Rocabert, J.; Luna, A.; Blaabjerg, F. ...
IEEE transactions on power electronics,
11/2012, Letnik:
27, Številka:
11
Journal Article
Recenzirano
The enabling of ac microgrids in distribution networks allows delivering distributed power and providing grid support services during regular operation of the grid, as well as powering isolated ...islands in case of faults and contingencies, thus increasing the performance and reliability of the electrical system. The high penetration of distributed generators, linked to the grid through highly controllable power processors based on power electronics, together with the incorporation of electrical energy storage systems, communication technologies, and controllable loads, opens new horizons to the effective expansion of microgrid applications integrated into electrical power systems. This paper carries out an overview about microgrid structures and control techniques at different hierarchical levels. At the power converter level, a detailed analysis of the main operation modes and control structures for power converters belonging to microgrids is carried out, focusing mainly on grid-forming, grid-feeding, and grid-supporting configurations. This analysis is extended as well toward the hierarchical control scheme of microgrids, which, based on the primary, secondary, and tertiary control layer division, is devoted to minimize the operation cost, coordinating support services, meanwhile maximizing the reliability and the controllability of microgrids. Finally, the main grid services that microgrids can offer to the main network, as well as the future trends in the development of their operation and control for the next future, are presented and discussed.
This paper presents a new multiresonant frequency-adaptive synchronization method for grid-connected power converters that allows estimating not only the positive- and negative-sequence components of ...the power signal at the fundamental frequency but also other sequence components at other harmonic frequencies. The proposed system is called MSOGI-FLL since it is based on both a harmonic decoupling network consisting of multiple second-order generalized integrators (MSOGIs) and a frequency-locked loop (FLL), which makes the system frequency adaptive. In this paper, the MSOGI-FLL is analyzed for single- and three-phase applications, deducing some key expressions regarding its stability and tuning. Moreover, the performance of the MSOGI-FLL is evaluated by both simulations and experiments to show its capability for detecting different harmonic components in a highly polluted grid scenario.
There is a strong trend in the photovoltaic inverter technology to use transformerless topologies in order to acquire higher efficiencies combining with very low ground leakage current. In this ...paper, a new topology, based on the H-bridge with a new ac bypass circuit consisting of a diode rectifier and a switch with clamping to the dc midpoint, is proposed. The topology is simulated and experimentally validated, and a comparison with other existing topologies is performed. High conversion efficiency and low leakage current are demonstrated.
Congenital myasthenic syndromes (CMS) are genetic disorders characterised by impaired neuromuscular transmission. This review provides an overview on CMS and highlights recent advances in the field, ...including novel CMS causative genes and improved therapeutic strategies. CMS due to mutations in
and
, impairing the synthesis and recycling of acetylcholine, have recently been described. In addition, a novel group of CMS due to mutations in
,
,
, and
encoding molecules implicated in synaptic vesicles exocytosis has been characterised. The increasing number of presynaptic CMS exhibiting CNS manifestations along with neuromuscular weakness demonstrate that the myasthenia can be only a small part of a much more extensive disease phenotype. Moreover, the spectrum of glycosylation abnormalities has been increased with the report that
mutations can cause CMS, thus bridging myasthenic disorders with dystroglycanopathies. Finally, the discovery of
mutations and laminin α5 deficiency has helped to draw attention to the role of extracellular matrix proteins for the formation and maintenance of muscle endplates. The benefit of β2-adrenergic agonists alone or combined with pyridostigmine or 3,4-Dyaminopiridine is increasingly being reported for different subtypes of CMS including AChR-deficiency and glycosylation abnormalities, thus expanding the therapeutic repertoire available.
Virtual inertia is known as an inevitable part of the modern power systems with high penetration of renewable energy. Recent trend of research is oriented in different methods of emulating the ...inertia to increase the sustainability of the system. In the case of dynamic performance of power systems especially in Automatic Generation Control (AGC) issue, there are concerns considering the matter of virtual inertia. This paper proposes an approach for analyzing the dynamic effects of virtual inertia in two-area AC/DC interconnected AGC power systems. Derivative control technique is used for higher level control application of inertia emulation. This method of inertia emulation is developed for two-area AGC system, which is connected by parallel AC/DC transmission systems. Based on the proposed technique, the dynamic effect of inertia emulated by storage devices for frequency and active power control are evaluated. The effects of frequency measurement delay and phase-locked loop effect are also considered by introducing a second-order function. Simulations performed by MATLAB software demonstrate how virtual inertia emulation can effectively improve the performance of the power system. A detailed eigenvalue analysis is also performed to support the positive effects of the proposed method.
Climbers germinate on the ground but need external support to sustain their stems, which are maintained attached to supports through modified organs, that is, climbing mechanisms. Specialized ...climbing mechanisms have been linked to higher diversification rates. Also, different mechanisms may have different support diameter restrictions, which might influence climbers' spatial distribution. We test these assumptions by linking climbing mechanisms to the spatiotemporal diversification of neotropical climbers. A dataset of climbing mechanisms is presented for 9071 species. WCVP was used to standardize species names, map geographical distributions, and estimate diversification rates of lineages with different mechanisms. Twiners appear concentrated in the Dry Diagonal of South America and climbers with adhesive roots in the Chocó region and Central America. However, climbing mechanisms do not significantly influence the distribution of neotropical climbers. Also, we found no strong support for correlations between specialized climbing mechanisms and higher diversification rates. Climbing mechanisms do not strongly impact the spatiotemporal diversification of neotropical climbers on a macroevolutionary scale. We argue that the climbing habit is a synnovation, meaning the spatiotemporal diversification it promotes is due to the sum effect of all the habit's traits rather than isolated traits, such as climbing mechanisms.
This paper demonstrates how the range of stable power transfer in weak grids with voltage source converters (VSCs) can be extended by modifying the grid synchronisation mechanism of a conventional ...synchronous reference frame phase locked loop (PLL). By introducing an impedance-conditioning term in the PLL, the VSC control system can be virtually synchronised to a stronger point in the grid to counteract the instability effects caused by high grid impedance. To verify the effectiveness of the proposed approach, the maximum static power transfer capability and the small-signal stability range of a system with a VSC HVDC terminal connected to a weak grid are calculated from an analytical model with different levels of impedance-conditioning in the PLL. Such calculations are presented for two different configurations of the VSC control system, showing how both the static power transfer capability and the small-signal stability range can be significantly improved. The validity of the stability assessment is verified by time-domain simulations in the Matlab/Simulink environment.
Chemical and transgenic approaches can activate ABA signalling via crop PYR/PYL ABA receptors; quinabactin can selectively activate tomato ABA receptors, and overexpression of monomeric-type ...receptors confers enhanced plant drought resistance.
Manipulating properties of matter at the nanoscale is the essence of nanotechnology, which has enabled the realization of quantum dots, nanotubes, metamaterials, and two-dimensional materials with ...tailored electronic and optical properties. Two-dimensional semiconductors have revealed promising perspectives in nanotechnology. However, the tunability of their physical properties is challenging for semiconductors studied until now. Here we show the ability of morphological manipulation strategies, such as nanotexturing or, at the limit, important surface roughness, to enhance light absorption and the luminescent response of atomically thin indium selenide nanosheets. Besides, quantum-size confinement effects make this two-dimensional semiconductor to exhibit one of the largest band gap tunability ranges observed in a two-dimensional semiconductor: from infrared, in bulk material, to visible wavelengths, at the single layer. These results are relevant for the design of new optoelectronic devices, including heterostructures of two-dimensional materials with optimized band gap functionalities and in-plane heterojunctions with minimal junction defect density.
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