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Agostini, C. A., Armijo, F. A., Silva, C., & Nasirov, S. (2021). The role of frequency regulation remuneration schemes in an energy matrix with high penetration of renewable energy. Renew. Energy, 171, 1097–1114.
Abstract: Renewable energies (RE) in Chile and around the world have experienced outstanding growth in recent years. However, RE technologies such as solar photovoltaic and wind generate an imbalance between generation (offer) and consumption (demand) because of their intermittent and variable nature. Moreover, RE & rsquo;s natural variability makes it necessary for conventional technologies to play a significant role in adjusting for the imbalance in the electric system frequency. As variable RE penetration grows, the need for frequency regulation will increase and, depending on how those higher costs are financed, this could lead to a disincentive to invest in conventional plants that provide that service. In this paper we study the impact of increased photovoltaic energy penetration, the leading RE in Chile, on the profitability of different conventional generation technologies. Specifically, we analyze the role that the frequency control remuneration mechanism has on that impact. For this purpose, four different solar photovoltaic penetration scenarios are simulated in Chile & rsquo;s Northern System, comparing two payment criteria for frequency regulation services: i) a cost-based pricing system whose payments relate to the incurred costs and ii) a market-based pricing system where the marginal cost of providing the services is paid. The results show that as installed photovoltaic capacity increases, the average marginal cost of energy (operation cost) decreases due to a displacement of more expensive power plants, but at the same time, investment cost may increase. In the long run, contract prices change as a result of falling operational costs and rising investment cost, resulting in changes in the profitability of all technologies. Finally, while both cost-based and market-based systems reward the ability to regulate frequency, the technologies performing the regulation receive different payments for the service, affecting both their profitability and the incentives for investment.
Keywords: Renewable energy; Frequency control; Ancillary services; Chile
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Beya-Marshall, V., Arcos, E., Seguel, O., Galleguillos, M., & Kremer, C. (2022). Optimal irrigation management for avocado (cv. 'Hass') trees by monitoring soil water content and plant water status. Agric. Water Manag., 271, 107794.
Abstract: Irrigation scheduling based on soil water content (Ow) sensors requires that Ow be maintained within a range (management lines) that is optimal for plant growth. The lower limit or “breaking point ” is determined following the soil water content dynamics on the transition of a rapid rate of depletion to a slower, under similar reference evapotranspiration. Although this criterion is practical, its implementation should be validated with plant water status measurement that contemplate weather condition, such as stem water potential “non-stressed ” baseline (Tx as a function of vapor-pressure deficit (VPD) in Ow conditions that do not limit yield). A study was con-ducted on a mature cv. 'Hass' avocado orchard in Central Chile during two seasons. There were 5 irrigation treatments: T1, Control; T2 and T3 with 29% less and 25% more of what was applied in T1, respectively; T4 and T5 same as Control until first and second fruit drop abscission, respectively, and then with 29% less. T1 trees were irrigated using a continuous frequency domain reflectometry (FDR) probe to maintain the root zone be-tween field capacity and the breaking point. There was biweekly monitoring of the Ow prior to irrigation, Tx and VPD. The Tx decline proportional to the intensity and the timing of water restriction; however, no treatment affected the crop load in either season. T2 did not show significant detrimental in fruit size, production and maturation, despite that frequently reached water content levels at the limit of the breaking point, and showed lower levels of stem water potential than Control, being the treatment with the highest water productivity. The results confirm that breaking point is an effective criterion to establish irrigation management. Additionally, when comparing the baseline for our non-stressed trees with a baseline from full irrigation treatments obtained from the literature, 30% water savings were achieved.
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Carrasco, M., Toledo, P. A., Velazquez, R., & Bruno, O. M. (2020). Automatic Stomatal Segmentation Based on Delaunay-Rayleigh Frequency Distance. Plants-Basel, 9(11), 1613.
Abstract: The CO2 and water vapor exchange between leaf and atmosphere are relevant for plant physiology. This process is done through the stomata. These structures are fundamental in the study of plants since their properties are linked to the evolutionary process of the plant, as well as its environmental and phytohormonal conditions. Stomatal detection is a complex task due to the noise and morphology of the microscopic images. Although in recent years segmentation algorithms have been developed that automate this process, they all use techniques that explore chromatic characteristics. This research explores a unique feature in plants, which corresponds to the stomatal spatial distribution within the leaf structure. Unlike segmentation techniques based on deep learning tools, we emphasize the search for an optimal threshold level, so that a high percentage of stomata can be detected, independent of the size and shape of the stomata. This last feature has not been reported in the literature, except for those results of geometric structure formation in the salt formation and other biological formations.
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Cordova, S., Canizares, C., Lorca, A., & Olivares, D. E. (2021). An Energy Management System With Short-Term Fluctuation Reserves and Battery Degradation for Isolated Microgrids. IEEE Trans. Smart Grid, 12(6), 4668–4680.
Abstract: Due to the low-inertia and significant renewable generation variability in isolated microgrids, short time-scale fluctuations in the order of seconds can have a large impact on a microgrid's frequency regulation performance. In this context, the present paper presents a mathematical model for an Energy Management System (EMS) that takes into account the operational impact of the short-term fluctuations stemming from renewable generation rapid changes, and the role that renewable curtailment and batteries, including their degradation, can play to counter-balance these variations. Computational experiments on the real Kasabonika Lake First Nation microgrid and CIGRE benchmark test system show the operational benefits of the proposed EMS, highlighting the need to properly model short-term fluctuations and battery degradation in EMS for isolated microgrids with significant renewable integration.
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Cordova, S., Canizares, C. A., Lorca, A., & Olivares, D. E. (2022). Frequency-Constrained Energy Management System for Isolated Microgrids. IEEE Trans. Smart Grid, 13(5), 3394–3407.
Abstract: Second-to-second power imbalances stemming from renewable generation can have a large impact on the frequency regulation performance of isolated microgrids, as these are characterized by low inertia and, more commonly nowadays, significant renewable energy penetration. Thus, the present paper develops a novel frequency-constrained Energy Management System (EMS) that takes into account the impact of short-term power fluctuations on the microgrid's operation and frequency regulation performance. The proposed EMS model is based on accurate linear equations describing frequency deviation, rate-of-change-of-frequency, and regulation provision in daily microgrid operations. Dynamic simulations on a realistic CIGRE benchmark test system show the economic and reliability benefits of the presented EMS model, highlighting the need of incorporating fast power fluctuations and their impact on frequency dynamics in EMSs for sustainable isolated microgrids.
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Fernandes, R. B., Mulders, G. D., Pascucci, I., Bergsten, G. J., Koskinen, T. T., Hardegree-Ullman, K. K., et al. (2022). pterodactyls: A Tool to Uniformly Search and Vet for Young Transiting Planets in TESS Primary Mission Photometry. Astron. J., 164(3), 78.
Abstract: Kepler's short-period exoplanet population has revealed evolutionary features such as the Radius Valley and the Hot Neptune desert that are likely sculpted by atmospheric loss over time. These findings suggest that the primordial planet population is different from the Gyr-old Kepler population, and motivates exoplanet searches around young stars. Here, we present pterodactyls, a data reduction pipeline specifically built to address the challenges in discovering exoplanets around young stars and to work with TESS Primary Mission 30-minute cadence photometry, since most young stars were not preselected TESS two-minute cadence targets. pterodactyls builds on publicly available and tested tools in order to extract, detrend, search, and vet transiting young planet candidates. We search five clusters with known transiting planets: the Tucana-Horologium Association, IC 2602, Upper Centaurus Lupus, Ursa Major, and Pisces-Eridani. We show that pterodactyls recovers seven out of the eight confirmed planets and one out of the two planet candidates, most of which were initially detected in two-minute cadence data. For these clusters, we conduct injection-recovery tests to characterize our detection efficiency, and compute an intrinsic planet occurrence rate of 49% +/- 20% for sub-Neptunes and Neptunes (1.8-6 R (circle plus)) within 12.5 days, which is higher than Kepler's Gyr-old occurrence rates of 6.8% +/- 0.3%. This potentially implies that these planets have shrunk with time due to atmospheric mass loss. However, a proper assessment of the occurrence of transiting young planets will require a larger sample unbiased to planets already detected. As such, pterodactyls will be used in future work to search and vet for planet candidates in nearby clusters and moving groups.
Keywords: POWERED MASS-LOSS; ZODIACAL EXOPLANETS; RADIUS DISTRIBUTION; DWARF; HUNT; STAR; FREQUENCY; EFFICIENT; KEPLER; SYSTEM
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Leiva, V., Saulo, H., Leao, J., & Marchant, C. (2014). A family of autoregressive conditional duration models applied to financial data. Comput. Stat. Data Anal., 79, 175–191.
Abstract: The Birnbaum-Saunders distribution is receiving considerable attention due to its good properties. One of its extensions is the class of scale-mixture Birnbaum-Saunders (SBS) distributions, which shares its good properties, but it also has further properties. The autoregressive conditional duration models are the primary family used for analyzing high-frequency financial data. We propose a methodology based on SBS autoregressive conditional duration models, which includes in-sample inference, goodness-of-fit and out-of-sample forecast techniques. We carry out a Monte Carlo study to evaluate its performance and assess its practical usefulness with real-world data of financial transactions from the New York stock exchange. (C) 2014 Elsevier B.V. All rights reserved.
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Urbina, F., Franco, A. F., & Concha, A. (2022). Frequency dynamics of a chain of magnetized rotors: dumbbell model vs Landau-Lifshitz equation. J. Phys. Condens. Matter, 34(48), 485801.
Abstract: During the past decades magnetic materials and structures that span several length scales have been of interest mainly due to their application in data storage and processing, flexible electronics, medicine, between others. From a microscopic point of view, these systems are typically studied using the Landau-Lifshitz equation (LLE), while approaches such as the dumbbell model are used to study macroscopic magnetic structures. In this work we use both the LLE and the dumbbell model to study spin chains of various lengths under the effect of a time dependent-magnetic field, allowing us to compare qualitatively the results obtained by both approaches. This has allowed us to identify and describe in detail several frequency modes that appear, with additional modes arising as the chain length increases. Moreover, we find that high frequency modes tend to be absorbed by lower frequency ones as the amplitude of the field increases. The results obtained in this work are of interest not only to better understand the behavior of the macroscopic spins chains, but also expands the available tools for qualitative studies of both macroscopic and microscopic versions of the studied system, or more complex structures such as junctions or lattices. This would allow to study the qualitative behavior of microscopic systems (e.g. nanoparticles) using macroscopic arrays of magnets, and vice versa.
Keywords: macroscopic system; magnetic rotors; frequency modes
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