Modelling, Analysis and Experimental Validation of Clock Drift Effects in Low-Inertia Power Systems

Clock drift in digital controllers is of great relevance in many applications. Since almost all real clocks exhibit drifts, this applies in particular to networks composed of several individual units, each of which being operated with its individual clock. In the present paper, we demonstrate via extensive experiments on a microgrid in the megawatt range that clock drifts may impair frequency synchronization in low-inertia power systems. The experiments also show that-in the absence of a common clock-the standard model of an inverter as an ideal voltage source does not capture this phenomenon. As a consequence, we derive a suitably modified model of an inverter-interfaced unit that incorporates the phenomenon of clock drifts. By using the derived model, we investigate the effects of clock drifts on the performance of droop-controlled grid-forming inverters with regard to frequency synchronization and active power sharing. The modeling and analysis is validated via extensive experiments on a microgrid in the megawatt range

Claros varones de Castilla ; y Letras

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-2010Sign. : [calderón]|p8|s, A-V\p8\s, X\p4\s .Marca tip. en port

Droop-controlled inverter-based microgrids are robust to clock drifts

Clock drift in digital controllers is of great relevance in many applications. Since almost all real clocks exhibit drifts, this applies in particular to networks composed of several individual units, each of which being operated with its individual clock. In the present work, we investigate the effect of clock drifts in inverter-based microgrids. Via a suitable model that incorporates this phenomenon, we prove that clock inaccuracies hamper synchronization in microgrids, in which the individual inverters are operated with a fixed uniform constant electrical frequency. In addition, we show that the well-known frequency droop control renders stability of a lossless microgrid robust with respect to clock inaccuracies. This claim is established by using stability results reported previously by the authors for lossless inverter-based microgrids with ideal clocks. We also discuss the effect of clock drifts on active power sharing. The analysis is illustrated via a simulation example

Company family, innovation and colombian graphic industry: a bayesian estimation of a logistical model

This study presents a comparative analysis of the management of innovation among family and non-family companies of the Graphic Communication Industry in Colombia. For which a questionnaire was applied in order to know the divergences in the innovation process carried out by these two types of organizations. From this, the methodology of Generalized Linear Models (MLG) was used and the Bayesian inference was used on the parameters of the model, analyzing the effect of the family business, the products that commercialize on the management of innovation in goods observed as a product tangible Obtaining in this way, the identification of some characteristics of innovation management and divergences with non-family companies, among them: a tendency towards the type of preferred innovation, the different sources and objectives to innovate, and the factors that hinder its process of innovation

Bird pollination of Canary Island endemic plants

The Canary Islands are home to a guild of endemic, threatened bird pollinated plants. Previous work has suggested that these plants evolved floral traits as adaptations to pollination by flower specialist sunbirds, but subsequently they appear to be have co-opted passerine birds as sub-optimal pollinators. To test this idea we carried out a quantitative study of the pollination biology of three of the bird pollinated plants, Canarina canariensis (Campanulaceae), Isoplexis canariensis (Veronicaceae) and Lotus berthelotii (Fabaceae), on the island of Tenerife. Using colour vision models, we predicted the detectability of flowers to bird and bee pollinators. We measured pollinator visitation rates, nectar standing crops, as well as seed set and pollen removal and deposition. These data showed that the plants are effectively pollinated by non-flower specialist passerine birds that only occasionally visit flowers. The large nectar standing crops and extended flower longevities (>10days) of Canarina and Isoplexis suggests that they have evolved bird pollination system that effectively exploits these low frequency non-specialist pollen vectors and is in no way suboptimal. Seed set in two of the three species was high, and was significantly reduced or zero in flowers where pollinator access was restricted. In L. berthelotii, however, no fruit set was observed, probably because the plants were self incompatible horticultural clones of a single genet. We also show that, while all three species are easily detectable for birds, the orange Canarina and the red Lotus (but less so the yellow-orange Isoplexis) should be difficult to detect for insect pollinators without specialised red receptors, such as bumblebees. Contrary to expectations if we accept that the flowers are primarily adapted to sunbird pollination, the chiffchaff (Phylloscopus canariensis) was an effective pollinator of these species

Paradoxas christianas contra las falsas opiniones del mundo

Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-2010Sign. : [asterisco]\p8\s, A-2F\p4\s, 2G-2I\p4\sPort. con esc. xil. episcopal del autor.Hojas escritas por ambas carasTexto con doble fileteado.Las il. son esc. xil. del autor en: h. con sing. [asterisco]3 v., en h. 231 v. y en h. 2I3 v

Título: Generaciones y semblanzas del noble caballero Fernan Perez de Guzman

Generaciones, semblanzas é obras de los excelentes Reyes de España D. Enrique III y D. Juan el II y de los venerables Perlados, y notables Caballeros que en los tiempos de estos Reyes fueron / ordenadas por el noble caballero Fernán Pérez de Guzmán, corregidas y emendadas y adicionadas por el Doctor Lorenzo Galindez de Carbajal.Autor tomado de Palau, 359009 su verdadero nombre, sin embargo, es Juan Antonio de Vera y AvilaCopia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2009-2010Marca de imp. en port.Sign.: [calderón]8, A-Z8, 2A-2C8, 2D

A protective personal factor against disability and dependence in the elderly: an ordinal regression analysis with nine geographically-defined samples from Spain

Background Sense of Coherence (SOC) is defined as a tendency to perceive life experiences as comprehensible, manageable and meaningful. The construct is split in three major domains: Comprehensibility, Manageability, and Meaningfulness. SOC has been associated with successful coping strategies in the face of illness and traumatic events and is a predictor of self-reported and objective health in a variety of contexts. In the present study we aim to evaluate the association of SOC with disability and dependence in Spanish elders. Methods A total of 377 participants aged 75 years or over from nine locations across Spain participated in the study (Mean age: 80.9 years; 65.3% women). SOC levels were considered independent variables in two ordinal logistic models on disability and dependence, respectively. Disability was established with the World health Organization-Disability Assessment Schedule 2.0 (36-item version), while dependence was measured with the Extended Katz Index on personal and instrumental activities of daily living. The models included personal (sex, age, social contacts, availability of an intimate confidant), environmental (municipality size, access to social resources) and health-related covariates (morbidity). Results High Meaningfulness was a strong protective factor against both disability (Odds Ratio [OR] = 0.50; 95% Confidence Interval [CI] = 0.29–0.87) and dependence (OR = 0.33; 95% CI = 0.19–0.58) while moderate and high Comprehensibility was protective for disability (OR = 0.40; 95% CI = 0.22–0.70 and OR = 0.39; 95%CI = 0.21–0.74), but not for dependence. Easy access to social and health resources was also highly protective against both disability and dependence. Conclusions Our results are consistent with the view that high levels of SOC are protective against disability and dependence in the elderly. Elderly individuals with limited access to social and health resources and with low SOC may be a group at risk for dependence and disability in Spain.This project was partially funded by a research contract in support of the project “Epidemiological Study of Dementia in Spain” signed by the Pfizer Foundation and Carlos III Institute of HealthS