Editorial: Grid Connection of Converters in Renewable Applications

Energy generated from renewable sources is fed into the grid by means of electronic power converters. These can be supervised at system (grid) level to coordinate all productions points together with storages and loads. Regulations impose power supply quality requirements regarding harmonics, grid fault response and low voltage ride through (LVRT). The progress of distributed generation presents challenges to converters such as island mode operation, voltage and frequency regulation, simulation, etc. New collaborative solutions for “more smart” microgrids must be included to improve power quality, reliability, service quality and duty. Wind turbines employing double-fed induction generators (DFIG) use two converters, one for the rotor side and one for the generator side. To improve the performance during severe grid failures, in Okedu and Barghash the advantages of using alternative configurations to the two-level converter, such as the parallel interleaved 2-level inverter, and the 3-level inverter, have been investigated. It has also been investigated to replace the classical dq-PLL with a new PLL, and to include a series dynamic braking resistor (SDBR) between the converters and the three-phase connections. Wind turbines must meet strict requirements, in terms of their behavior, in the event of grid failures, which are regulated by the LVRT regulations in each country. These regulations indicate, by means of voltage and time graphs, how long the wind turbines must remain connected depending on the depth of the faults. In addition, the limits of active and reactive power that can be exchanged during faults are established. The aim is to avoid cascading disconnections of wind turbines that would compromise the stability of the grid. In Okedu and Barghash, the effect of various elements in improving the behaviour of a DFIG against grid faults has been investigated. The first of these elements is the parameters of the IGBTs, concluding that the on-resistance has the greatest influence. The second is the use of a new PLL, and the third is the use of a SDBR during a grid failure. It was found that all of them could improve the performance of the generator in the event of a grid failure. When a wind turbine uses a permanent magnet synchronous generator (PMSG), 100% of the energy generated passes through both converters. In Okedu and Barghash, the control systems of the generator-side and grid-side converters have been considered; several scenarios regarding the turn on resistance of the IGBTs have been considered, and their behaviour during grid faults has been analysed. Generator performance has also been studied with and without the use of a DC-DC converter for overvoltage protection. The main generators used in wind turbines are DFIG and PMSG. In Okedu et al., a comparison of the behaviour of both wind turbines against grid faults has been carried out in various scenarios with different values of generator parameters. The number of converters, associated with renewable generation, connected to the grid has increased significantly lately. This can affect the dynamic response, especially during disturbances, but it can also provide new grid support functionalities if information on the oscillation characteristics is available. Through the use of artificial intelligence, in Baltas et al. the abilities to predict and damp electromechanical oscillations have been improved. With the constant increase in the number of wind turbines connected to the grid, it is very important to have the ability to maintain grid frequency control. In Okedu and Barghash, a work has been presented to stabilise the wind farm during periods of wind speed change by using capacitors connected via a DC-DC converter and a grid-connected DC-AC converter. It was concluded that higher values of the DC-DC converter time constant lead to better performances during load transients. A system including two steam turbines and two squirrel cage induction generators was used in the experiments. Microgrids bring power generation closer to the places of consumption to reduce the saturation of distribution lines. They consist of renewable generation, energy storage and fossil fuel generation. They have three levels of control, where the primary level is the closest to the converters, and the tertiary level, the most external and slowest, performs general monitoring functions. The paper (Buraimoh et al.) focuses on the secondary control functions related to grid failure performance. It proposes a distributed control between inverters and is based on fast detection techniques (fast Delayed Signal Cancellation, DSC), with the objective of a fast control of active and reactive power. A robust transition method between fault mode and normal mode is proposed. Accurate coordination and power sharing between distributed energy resources is achieved. Some energy conversion systems are so complex that they are very difficult to build and test in the laboratory. These include the study of high voltage direct current (HVDC) transmission when several modular multilevel converters (MMC) are involved together with DC grid failure protection elements. In Wang et al., a system including a simulated part (two digitally simulated MMC) and a physical part (two MMC) has been experimented with. The coupling between the two parts has been carried out by means of A/D and D/A converters and power amplifiers

Control and synchronization algorithms for a grid-connected photovoltaic system under harmonic distortions, frequency variations and unbalances

In this paper, an implementation of the control and the synchronization algorithms for a Voltage Source Inverter used as the power conditioner for Photovoltaic renewable energy in a grid-connected structure is carried out. Its main purpose is to show, in a simple manner, the design and combined operation of the control and synchronization algorithms for attaining the proper behaviour of the Grid Inverter when the 3-phase utility grid is disturbed by voltage unbalances, frequency variations and harmonic distortions, according to power quality standards. In order to obtain a high efficiency of the system during perturbations, a Proportional Resonant controller with a Harmonic Compensator structure is designed for the control algorithm, whereas a Dual Second Order Generalized Integrator Frequency-Locked Loop (DSOGI-FLL) is used as the synchronization algorithm. In order to validate both the control and the synchronization algorithms, some simulations using MATLAB/SIMULINK from The MathWorks, Inc. are shown firstly, and secondly, some real-time digital simulations are carried out.This work has been supported by a grant from La Fundación Séneca, Agencia de Ciencia y Tecnología de la Región de Murcia, Spain, as a part of the Project Ref.11948/PI/09, entitled “Design and construction of a hardware/software prototype for the synchronization and monitoring of renewable agents in a Distributed Generation System” (Alexis. B. Rey-Boué), and a scholarship towards the PhD degree from the Universidad Politécnica de Cartagena, Spain, with the Santander Bank support (N. F. Guerrero-Rodríguez)

ANÁLISE DE PARÂMETROS FÍSICO-QUÍMICOS DE ÁGUAS SUBTERRÂNEAS DA ZONA LESTE DE PRESIDENTE PRUDENTE/SP ENTRE OS ANOS 2018 E 2019

ANALYSIS OF PHYSICAL AND CHEMICAL PARAMETERS OF UNDERGROUND WATER IN THE EAST ZONE OF PRESIDENTE PRUDENTE/SP BETWEEN THE YEARS 2018 AND 2019ANÁLISIS DE PARÁMETROS FÍSICOS Y QUÍMICOS DE AGUAS SUBTERRÁNEAS EN LA ZONA ESTE DE PRESIDENTE PRUDENTE/SP ENTRE LOS AÑOS 2018 Y 2019RESUMOO objetivo deste trabalho foi verificar o processo de urbanização da zona leste de Presidente Prudente/SP em sua relação com a indisponibilidade de pleno saneamento básico, levando a um quadro de contaminação das águas subterrâneas. Para tanto, utilizou-se como indicadores da qualidade da água, parâmetros químicos e microbiológicos como o pH, condutividade, concentração de nitrato e coliformes fecais e totais. A pesquisa teve como base metodológica uma análise bibliográfica acerca do problema ora delineado, e posterior desenvolvimento da pesquisa experimental realizada nas regiões periféricas da zona leste de Presidente Prudente nos anos 2018 e 2019. Os resultados obtidos demonstram a presença de compostos químicos e microbiológicos indesejáveis, com enfoque na inadequação da presença de nitrogênio albuminoide e coliformes fecais e totais.Palavras-chave: Águas Subterrâneas; Urbanização; Uso da Água.ABSTRACTThis work aimed to verify the urbanization process of Presidente Prudente regarding unavailability of full sanitation, which led to contamination of groundwater, using as indicators of water quality, chemical and microbiological parameters, such as pH, conductivity, nitrate concentration as well as fecal and total coliforms. For that purpose, the research methodology was based on a bibliographical analysis of the problem outlined in this work, and later developed through experimental research carried out in the peripheral regions in the eastern zone of the city in 2018 and 2019. The results demonstrate the presence of undesirable chemical and microbiological compounds, focusing on the inadequacy due to the presence of albuminous nitrogen and fecal and total coliforms.Keywords: Groundwaters; Urbanization; Water Use.RESUMENEl objetivo de este trabajo fue verificar el proceso de urbanización de Presidente Prudente relacionado con la falta de saneamiento completo, que fue capaz de desarrollar una contaminación del agua subterránea, utilizando como indicadores de la calidad del agua, parámetros químicos y microbiológicos como el pH, la conductividad, la concentración de nitrato como así como coliformes fecales y totales. Para hacerlo, la investigación se basó en su metodología mediante un análisis bibliográfico sobre el problema descrito en este trabajo, y luego se desarrolló a través de la investigación experimental realizada en las regiones periféricas ubicadas en la zona este de la ciudad en 2018 y 2019. Por lo tanto, se obtuvieron resultados que demuestran la presencia de compuestos químicos y microbiológicos indeseables, centrándose en la insuficiencia del nitrógeno albuminoso y los coliformes fecales y totales.Palabras clave: Aguas subterráneas; Urbanización; Uso del agua

Calculation of the number of modules and the switching frequency of a modular multilevel converter using near level control

This paper is focused on the modular multilevel converter (MMC) topology that uses the near level control (NLC) method. Specifically, it addresses the relationship between the number of levels or switching modules, the switching frequency and the harmonics superimposed on the generated voltages and currents, making a comparison with the high and medium voltage AC codes. Furthermore, it also assesses the possibility of connecting the MMC to the electrical grid without using any coupling inductor, either using a transformer or simply directly. Finally, it shows how to automate the simulations necessary to select the number of levels and the switching frequency.This work has been partially supported by a grant from the Spanish Government as a part of Project Ref. TEC2016-80136-P, entitled “Nuevas topologías para convertidores en MT para grandes Instalaciones Fotovoltaicas” (A. B. Rey-Boué)

Enhanced controller for grid-connected modular multilevel converters in distorted utility grids

This paper is about the control of Modular multilevel converters, an innovative technology in the design of converters, which is beginning to be included in real installations. Papers about this topic include simulation models, circulating current reduction, voltage modulators, capacitor voltage balancing and control issues. The scheme for current source regulation used in this article includes all control loops, which are, from the outermost to innermost, DC bus voltage regulator, current regulator, voltage modulator, capacitor voltage balancing, and a PLL for the synchronization to the grid. Disposition-sinusoidal pulse width modulation is used as the voltage modulator, and an enhanced control strategy in the stationary reference frame for 3-phase MMCs is used for the inner current control loops. Very detailed simulations of the complete control system have been performed for both the enhanced control strategy in the stationary reference frame, and the well-known control in the synchronous reference frame, as well as some experiments using the hardware-in-the-loop simulation technique. The validation of these control strategies is made by a comparison of the capability of each one to compensate the harmonic distortions of the utility grid according to the grid code. The correct operation has been tested in the case of a strong/weak grid, unbalances and grid failures.This work has been partially supported by a grant from the Spanish Government as a part of 673 Project Ref. TEC2016-80136-P, entitled “Nuevas topologías para convertidores en MT para grandes 674 Instalaciones Fotovoltaicas” (A. B. Rey-Boué

Procedure for the Determination of the Student Workload and the Learning Environment Created in the Power Electronics Course Taught Through Project-Based Learning

In the research presented in this article, a procedure for determining student workload has been designed, tested, and validated. This procedure also makes it pos- sible to analyze how different teaching variables are affected by workload and to visualize the learning environment generated in the course. Background: When the project-based learning (PBL) method- ology is used in a course, if the students’ workload is not properly planned and controlled, important variables in the educational environment, such as the teaching organization and the students’ approach to learning, can be affected. The PBL methodology may even become unfeasible as it affects the other courses with which it shares year and semester. This justifies the need to know the student workload of a subject. The previous research has presented procedures for establishing student workload. However, they use questionnaires with a high number of questions. A ques- tionnaire with many questions affects the reliability of students’ answers. The questionnaire presented in this article reduces the number of questions without affecting the results obtained and it is easily applicable to other courses. Research Questions: The questions to be answered in this research are: 1) is the workload of the students, when using the PBL methodology in a course, in line with the one established in the syllabus? and 2) is the learning environment created in the course as expected? Methodology: The methodology used to obtain the necessary data is based on students completing weekly surveys, two critical incident questionnaires (CIQs), and a final survey. The aim was always to minimize the number of questions to be answered, ensuring that the data collected provided a true picture of the workload and the educational environment. Findings: The analysis of the data obtained by applying the procedure provides mechanisms to control the workload, ensure involvement and motivation, improve students’ academic results and show the learning environment created in the course. The implementation of this method, during three academic years, has allowed to test its effectiveness, validate some of the initial hypotheses, and confirm the conclusions of some previous studies

RNA-SEQ of fv-induced erythroleukemia cells suggests a role of wasp.

The goal of research is analyze the molecular function of was in progenitors of the erythoid linage and its role in reprogramming celular differentiation in erythroleukemia cells.CONACYT - Consejo Nacional de Ciencias y TecnologíaPROCIENCI

Joint effect of physical activity and sedentary behaviour on cardiovascular risk factors in Chilean adults

Background: To investigate the associations between combined categories of moderate-to-vigorous physical activity (MVPA) and sedentary behaviour (SB) with markers of adiposity and cardiovascular risk in adults. Methods: Overall, 5040 participants (mean age 46.4 years and 59.3% women) from the cross-sectional Chilean National Health Survey 2009–2010 were included in this study. MVPA and SB were measured using the Global Physical Activity questionnaire. Four categories were computed using MVPA- and SB-specific cut-offs (‘High-SB & Active’, ‘Low-SB & Active’, ‘High-SB & Inactive’ and ‘Low-SB & Inactive’). Results: Compared to the reference group (‘High-SB & Inactive’), those in ‘High-SB & Active’ and ‘Low-SB & Active’ were less likely to have an obese BMI (OR: 0.67 [0.54; 0.85], P = 0.0001 and 0.74 [0.59; 0.92] P = 0.0007, respectively) and less likely to have metabolic syndrome (OR: 0.63 [0.49; 0.82], P < 0.0001 and 0.72 [0.57; 0.91], P = 0.007), central obesity (OR: 0.79 [0.65; 0.96], P = 0.016 and 0.71 [0.59; 0.84], P < 0.0001), diabetes (OR: 0.45 [0.35; 0.59], P < 0.0001 and 0.44 [0.34; 0.56], P < 0.0001) and hypertension (OR: 0.52 [0.43; 0.63], P < 0.0001 and 0.60 [0.50; 0.72], P < 0.0001), respectively. Conclusions: Being physically active and spending less time in SBs was associated with lower adiposity and improvements in cardiovascular risk factors

ANÁLISE DE PARÂMETROS FÍSICO QUÍMICOS DE ÁGUAS SUBTERRÂNEAS DA ZONA LESTE DE PRESIDENTE PRUDENTE NO SEGUNDO SEMESTRE DE 2018

This work objective was to verify the process of Presidente Prudente urbanization related to the unavailability of full sanitation, which was able to  develop a contamination of groundwater, using as indicators of water quality, chemical and microbiological parameters such as pH, conductivity, nitrate concentration as well as fecal and total coliforms. In order to do so, the research was based in its methodology by a bibliographical analysis about the problem outlined in this work, and later developed through experimental research carried out in the peripheral regions located on the eastern zone of the city. Thus, there was obtained results that demonstrate the presence of undesirable chemical and microbiological compounds, focusing on the inadequacy of albuminous nitrogen and fecal and total coliforms.O objetivo deste trabalho foi verificar o processo de urbanização prudentino no sentido da zona leste em sua relação com a indisponibilidade de pleno saneamento básico, levando a um quadro de contaminação das águas subterrâneas. Para tanto, utilizou-se, como indicadores da qualidade da água, parâmetros químicos e microbiológicos como o pH, condutividade, concentração de nitrato e coliformes fecais e totais. A pesquisa se pautou, em sua metodologia, por uma análise bibliográfica acerca do problema ora delineado, posteriormente se desenvolvendo mediante pesquisa experimental realizada nas regiões periféricas da zona leste prudentina. Assim, obteve-se resultados que demonstram a presença de compostos químicos e microbiológicos indesejáveis, com enfoque da inadequação quanto ao nitrogênio albuminoide e coliformes fecais e totais

Utilización de los objetos de aprendizaje y su relación en el rendimiento académico de la asignatura de Física I

La utilización de los objetos de aprendizaje y su relación en el rendimiento académico de la asignatura de física I, en los estudiantes de primer semestre de la facultad de ingeniería de la Universidad Nacional de Chimborazo. El bajo rendimiento que el estudiante alcanza en física, por el nivel de exigencia que se aplica en la formación universitaria, generan dificultades en el dominio conceptual, así como en la apropiación de los métodos para su estudio, este trabajo propone, determinar la relación entre la utilización de los objetos de aprendizaje y el rendimiento académico en el estudio de la Dinámica de la partícula, el cual se realizó mediante una investigación de tipo correlacional y diseño Cuasi-experimental, la metodología propuesta se basó en el modelo de Diseño Instruccional que guie en la parte pedagógica en la que se recomienda el uso de algunas plantillas. Tomando en cuenta a los actores principales, como se puede apreciar, al realizar la prueba estadística de (z) para muestras independientes, se puede ver que efectivamente el grupo de estudiantes que utilizan los objetos de aprendizaje obtienen un rendimiento académico significativamente superior en comparación con los estudiantes que no usaron los objetos de aprendizaje. En la que se nota claramente la evolución de los logros de aprendizaje en cada uno de los estudiantes. La incorporación de los OA mejoró el rendimiento académico en los estudiantes de ingeniería que cursan la asignatura de física I en el estudio de la dinámica de la partícula, los OA mejoran el proceso de enseñanza- aprendizaje y elevan el rendimiento académico, involucrando a todos los estudiantes a un trabajo colaborativo y cooperativo