Simplified modeling of low voltage distribution networks for PV voltage impact studies

Distributed generation is increasingly being integrated into distribution networks worldwide, presenting new challenges for network operators and planners. In particular, the introduction of photovoltaic (PV) generation at the low voltage (LV) level has highlighted the ongoing need for more extensive and detailed modeling to quantify the full extent and nature of potential impacts. While a number of approaches have been developed to address the size of this problem, the most accurate and comprehensive approach is to carry out simulations for the entire network across multiple scenarios. However, this task is computationally complex and requires significant amounts of data. To address this challenge, this paper presents a simplified and computationally efficient methodology based around a two-bus equivalent model, which may be used to estimate the maximum voltage in an LV area due to PV generation over time. The developed model is validated against a full three-phase power flow approach for a real-world distribution network comprising 10 213 LV network areas. Furthermore, to highlight its utility, the model is used in a case study examining the effectiveness of reactive power injection for mitigating overvoltage due to PV generation.This work was supported in part by the Ministry of Business Innovation and Employment under Grant PROP-29328-EMRTR-UOC, in part by Transpower, and in part by the Electricity Engineers' Association for the GREEN Grid Project. Paper no. TSG-01192-2014.Publicad

SoL-A PV generation model for grid integration analysis in distribution networks

Photovoltaic (PV) generation systems are increasingly being integrated into distribution networks, presenting new challenges for network operators and planners. To fully quantify the impact of this distributed generation, power systems and control engineers are often required to model a large number of networks across multiple scenarios of PV uptake and allocation. However, due to the complexity of these network models and simulation methods, and the associated computational constraints, very simplified models are often adopted for solar irradiance, and PV module and inverter output power. These ad hoc models often utilise simple linear relationships, and are not validated against real data or more detailed models. The proposed model (SoL) is composed of pre-existing equations selected from the current state of the art models, as well as newly formulated equations. Each submodel is validated against pre-existing models using data from a number of meteorological sites around the world, showing good performance with reduced computational complexity. The resulting model is subsequently shown to be suitable for running large scale quasi-steady state power flow simulations and Monte Carlo analyses as required for grid integration studies.The authors would like to acknowledge the funding provided by theMinistry of Business Innovation and Employment, Transpower, and the EEA for the GREEN Grid project.Publicad

Validation and self-shading enhancement for SoL: A photovoltaic estimation model

The estimation of electrical power generation in photovoltaic (PV) grid-connected systems based on meteorological data is a nontrivial, highly useful task, for instance to achieve accurate energy assessment. Widely used PV generation simulators are PV Systems (PVsyst), System Advisor Model (SAM) and PVLib. These simulators are characterized by presenting numerous features and providing complete results, however the PV estimation model SoL is an example of a new approach to PV generation estimation. SoL is characterized by its simplicity and computational efficiency. The objective of this paper is validating the recently published SoL model using real data from two PV locations for several years and facilities and comparing the results with those of three other PV simulators, namely PVsyst (in Spain), SAM (in Denver) and PVLib (both). It has been found that SoL estimates power production accurately for both locations and its estimations are more precise than those given by PVsyst, SAM and PVLib. It proves to be more computationally efficient than PVsyst, it can work with higher resolutions than SAM and PVsyst and requires fewer inputs than PVLib, SAM or PVsyst. Finally, a self-shading model is proposed as an enhancement for the SoL model. The number of inputs required is minimal, and it is an approximate yet efficient model. The estimation when using the self-shading enhancement is even more accurate than the previous estimation for SoL in locations where self-shading is evident. SoL proves to be an appropriate model for power estimation, and its results are enhanced when using the self-shading model proposed in this paper.Publicad

Campaña de prospección en el valle del río Magro: corredor de Hortunas (Requena-Yátova, València)

Información preliminar sobre el poblamiento ibérico del corredor de Hortunas (Valencia)

Individual differences in thinking style and dealing with contradiction: The mediating role of mixed emotions

The present research examined how individuals' thinking style (holistic vs. analytic) is associated with the way they deal with contradictory information and whether experiencing mixed emotions can mediate this relationship. Participants first completed the thinking style measure and then were exposed to two contradictory pieces of information (Studies 1 and 2). In study 2, we also measured the experience of mixed emotions to test the mediating role of this variable. Across two studies, we found that individuals with a holistic thinking style were more able to reconcile contradictory information compared to individuals with an analytic thinking style. Study 2 showed that the relationship between thinking style and dealing with contradiction was mediated by the experience of mixed emotions. This research extends previous findings on confrontation of contradiction and mixed emotions by using an individual-differences rather than a cultural-differences approach, and establishes mixed emotions as a plausible mediating variable

Endogenous Approach of a Frequency-Constrained Unit Commitment in Islanded Microgrid Systems

Power reserves are usually scheduled in day-ahead unit commitment (UC) to minimize operating costs while maintaining system security. In applying basic UC (bUC) after a contingency, the system frequency may fall upon the activation of the load-shedding global control (under-frequency load-shedding or UFLS) limits. Small isolated microgrids are more sensitive to this issue due to their lack of inertia. Including dynamic considerations into the bUC problem can minimize UFLS activation and also avoid the need for the operator to later check the short-term feasibility of a bUC solution. These proposals are known as Frequency-Constrained UC (FCUC), although the implementation are very time-consuming. FCUC implementation will increase the system’s operational costs, which should be calculated to estimate remuneration to the safety service based on the additional reserve provision. The electrical system of Gran Canaria island has suffered several episodes of greater blackouts in recent years. Shortly, there will be 242 MW of wind generation installed (26% of the thermal power installed on Gran Canaria). The main objective of this work is to improve the island system reliability by means of an FCUC formulation applied by the system operator in practice, including renewable sources. The results show that the frequency values remained within the admissible boundaries, but the system’s operational costs increased by around 13%.This work was supported by VILLUM FONDEN under the VILLUM Investigator Grant (no. 25920): Center for Research on Microgrids (CROM); www.crom.et.aau.dk, accessed on 1 May 2021. 1-This work was supported by the Spanish Ministry of Innovation under Grant PID2019- 104449RB-I00. 2-This work was supported by VILLUM FONDEN under the VILLUM Investigator Grant (no. 25920): Center for Research on Microgrids (CROM); www.crom.et.aau.dk, accessed on 1 May 2021.Publicad

Microgrid and Distributed Energy Resources Standards and Guidelines Review: Grid Connection and Operation Technical Requirements

This article belongs to the Special Issue Analysis of Microgrid Integrated with Renewable Energy SystemIn this review, the state of the art of 23 distributed generation and microgrids standards has been analyzed. Among these standards, 18 correspond mainly to distributed generation while five of them introduce the concept of microgrid. The following topics have been considered: interconnection criteria, operating conditions, control capabilities, power quality, protection functions and reference variables. The revised national standards cover ten countries on four continents, which represents 80% of the countries with the largest installed renewable capacities. In addition, eight other relevant international standards have been analyzed, finding IEEE 1547 as the most comprehensive standard. It is identified a clear need to define a common framework for distributed energy resources (DERs) and microgrid standards in the future, wherein topics, terminology, and values are expressed in a manner that may widely cover the entire diversity in a way similar to how it has already been expressed at the network transport level by the ENTSO-E codes

On the number of pseudo-triangulations of certain point sets

We compute the exact number of pseudo-triangulations for two prominent point sets, namely the so-called double circle and the double chain. We also derive a new asymptotic lower bound for the maximal number of pseudotriangulations which lies significantly above the related bound for triangulations.Acciones Integradas 2003-2004Acción Integrada España-AustriaDirección General de Investigación Científic

A case study: characterization of physiological, cinematic and neuromuscular demands of handball referee during competition

El presente estudio pretende conocer y caracterizar las cargas de un árbitro de Balonmano durante la competición. La muestra se compone de dos árbitros que han participado en las finales infantil y cadete de la competición regional de la Federación Extremeña de Balonmano. Se ha comparado ambos árbitros en relación a una variable de carga interna (Frecuencia Cardiaca) y dos variables de carga externa (cinemáticas y neuromusculares). Los resultados obtenidos muestran que no existen diferencias significativas entre los dos árbitros en ninguna de las variables. Se recomienda continuar con esta línea de investigación en futuras publicaciones con el fin de poder proponer futuros programas de entrenamiento individualizados.The present study aims to know and characterize performance loads of the Handball referees during the competition. Two referees who have participated in the school league of the Extremadura Handball Federation compose the sample. Both referees have been compared in relation to internal load (Heart Rate) and external load variables (kinematic and neuromuscular performance). The results show that there are no significant differences between the two referee in any variables, and allow defining the performance requirements of Handball referees. This research line should be continued in future publications to establish individualized training programs for that population.peerReviewe