Black-start capability of PV power plants through a grid-forming control based on reactive power synchronization

Power system restoration is a critical process for any power system. As synchronous generators are being replaced by power electronic converters used in renewable energy generation, the contribution of renewable energy power plants to power system restoration (PSR) after a black-out is becoming more relevant, the so-called black start capability. Existing solutions for providing black start capability to photovoltaic (PV) power plants rely on the use of energy storage systems (ESS) in a hybrid PV plant. In contrast, this paper proposes a solution for the contribution of PV power plants to the PSR that allows a completely autonomous black start process. Reactive power synchronization is used for controlling the PV inverters as virtual synchronous generators (VSG), providing grid-forming control and ensuring synchronism. During the black start process, the PV power is regulated to match the demand using a decentralized solution to share the load between multiple PV inverters. The solution has been validated to handle the most critical situations during the black start process such as the variation on the power source, i.e. irradiance, or on the supplied load and the connection to the main grid.This paper was supported by the Spanish Research Agency under project reference PID2019-106028RB-I00/AEI/10.13039/501100011 033

Analysis of the converter synchronizing method for the contribution of battery energy storage systems to inertia emulation

This article belongs to the Special Issue Energy Storage for Grid Integration of Renewable Energy.This paper presents a comprehensive analysis of the effect of the converter synchronizing methods on the contribution that Battery Energy Storage Systems (BESSs) can provide for the support of the inertial response of a power system. Solutions based on phase-locked loop (PLL) synchronization and virtual synchronous machine (VSM) synchronization without PLL are described and then compared by using time-domain simulations for an isolated microgrid (MG) case study. The simulation results showed that inertial response can be provided both with and without the use of a PLL. However, the behavior in the first moments of the inertia response differed. For the PLL-based solutions, the transient response was dominated by the low-level current controllers, which imposed fast under-damped oscillations, while the VSM systems presented a slower response resulting in a higher amount of energy exchanged and therefore a greater contribution to the support of the system inertial response. Moreover, it was demonstrated that PLL-based solutions with and without derivative components presented similar behavior, which significantly simplified the implementation of the PLL-based inertia emulation solutions. Finally, results showed that the contribution of the BESS using VSM solutions was limited by the effect of the VSM-emulated inertia parameters on the system stability, which reduced the emulated inertia margin compared to the PLL-based solutions

Online machine learning algorithms to predict link quality in community wireless mesh networks

Producción CientíficaAccurate link quality predictions are key in community wireless mesh networks (CWMNs) to improve the performance of routing protocols. Unlike other techniques, online machine learning algorithms can be used to build link quality predictors that are adaptive without requiring a predeployment effort. However, the use of these algorithms to make link quality predictions in a CWMN has not been previously explored. This paper analyses the performance of 4 well-known online machine learning algorithms for link quality prediction in a CWMN in terms of accuracy and computational load. Based on this study, a new hybrid online algorithm for link quality prediction is proposed. The evaluation of the proposed algorithm using data from a real large scale CWMN shows that it can achieve a high accuracy while generating a low computational load.Ministerio de Economía, Industria y Competitividad (Project TIN2014-53199-C3-2-R)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA082U16

A self-scalable distributed network simulation environment based on cloud computing

Producción CientíficaWhile parameter sweep simulations can help undergraduate students and researchers to understand computer networks, their usage in the academia is hindered by the significant computational load they convey. This paper proposes DNSE3, a service oriented computer network simulator that, deployed in a cloud computing infrastructure, leverages its elasticity and pay-per-use features to compute parameter sweeps. The performance and cost of using this application is evaluated in several experiments applying different scalability policies, with results that meet the demands of users in educational institutions. Additionally, the usability of the application has been measured following industry standards with real students, yielding a very satisfactory user experience.Ministerio de Economía, Industria y Competitividad (Projects TIN2014-53199-C3-2-R and TIN2017-85179-C3-2-R)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. VA082U16

Reactive power synchronization method for voltage-sourced converters

There is a growing interest in the parallel operation of voltage source converters (VSCs) both in an isolated microgrid or connected to the utility grid. The most common solution in the literature for the paralellization of VSCs is the so-called droop control, which brings about a relationship between active power and frequency. In this paper, a different approach is proposed where reactive power is used instead of active power to ensure synchronous operation. Active and reactive power are independently controlled using a dq-frame representation based on the vector oriented control, which inherently provides current limitation capability. A detailed dynamic model of the system is used to demonstrate the relation between reactive power and frequency. Due to the intrinsic synchronizing mechanism, the proposed scheme can operate in both isolated and grid-connected modes. As opposed to droop control schemes, active power is not used for synchronization and thus synchronization is possible even if active power is not controllable. Simulation and experimental results, for a case study where a VSC is connected to a host grid, are presented to validate the proposal

Generating actionable predictions regarding MOOC learners’ engagement in peer reviews

Producción CientíficaPeer review is one approach to facilitate formative feedback exchange in MOOCs; however, it is often undermined by low participation. To support effective implementation of peer reviews in MOOCs, this research work proposes several predictive models to accurately classify learners according to their expected engagement levels in an upcoming peer-review activity, which offers various pedagogical utilities (e.g. improving peer reviews and collaborative learning activities). Two approaches were used for training the models: in situ learning (in which an engagement indicator available at the time of the predictions is used as a proxy label to train a model within the same course) and transfer across courses (in which a model is trained using labels obtained from past course data). These techniques allowed producing predictions that are actionable by the instructor while the course still continues, which is not possible with post-hoc approaches requiring the use of true labels. According to the results, both transfer across courses and in situ learning approaches have produced predictions that were actionable yet as accurate as those obtained with cross validation, suggesting that they deserve further attention to create impact in MOOCs with real-world interventions. Potential pedagogical uses of the predictions were illustrated with several examples.European Union’s Horizon 2020 research and innovation programme (Marie Sklodowska-Curie grant 793317)Ministerio de Ciencia, Innovación y Universidades (projects TIN2017-85179-C3-2-R / TIN2014-53199-C3-2-R)Junta de Castilla y León (grant VA257P18)Comisión Europea (grant 588438-EPP-1-2017-1-EL-EPPKA2-KA

Towards the Enactment of Learning Situations Connecting Formal and Non-Formal Learning in SLEs

Producción CientíficaSmart Learning Environments hold promise of adapting learning processes to the individual context of students and connecting formal with non-formal learning. To do so, SLEs need to know the current context of the students, regardless of the physical or virtual space where learning takes place. This paper presents an architecture that assists in the deployment and enactment of learning situations across-spaces, able to sense and react to changes in the students’ context in order to adapt the learning process.ICSLE 2019: International Conference on Smart Learning EnvironmentsAgencia Estatal de Investigación - Fondo Europeo de Desarrollo Regional (projects TIN2014-53199-C3-2-R / TIN2017-85179-C3-2-R)Comisión Europea (project 588438-EPP-1-2017-1-EL-EPPKA2-KA

Aligning learning design and learning analytics through instructor involvement: a MOOC case study

Producción CientíficaThis paper presents the findings of a mixed-methods research that explored the potentials emerging from aligning learning design (LD) and learning analytics (LA) during the design of a predictive analytics solution and from involving the instructors in the design process. The context was a past massive open online course, where the learner data and the instructors were accessible for posterior analysis and additional data collection. Through a close collaboration with the instructors, the details of the prediction task were identified, such as the target variable to predict and the practical constraints to consider. Two predictive models were built: LD-specific model (with features based on the LD and pedagogical intentions), and a generic model (with cumulative features, not informed by the LD). Although the LD-specific predictive model did not outperform the generic one, some LD-driven features were powerful. The quantity and the power of such features were associated with the degree to which the students acted as guided by the LD and pedagogical intentions. The leading instructor’s opinion about the importance of the learning activities in the LD was compared with the results of the feature importance analysis. This comparison helped identify the problems in the LD. The implications for improving the LD are discussed.Ministerio de Ciencia e Innovación (Proyect grants TIN2017-85179-C3-2-R and TIN2014-53199-C3-2-R)Junta de Castilla y León (programa de apoyo a proyectos de investigación - Ref. Project VA257P18)European Commission under project grant 588438-EPP-1-2017-1-EL-EPPKA2-KAEuropean Union’s Horizon 2020 under the Marie Sklodowska-Curie grant agreement 79331

To reward and beyond: Analyzing the effect of reward-basedstrategies in a MOOC

Producción CientíficaDespite the benefits of MOOCs (e.g., open access to education offered by prestigious universities), the low level of student engagement remains as an important issue causing massive dropouts in such courses. The use of reward-based gamification strategies is one approach to promote student engagement and prevent dropout. However, there is a lack of solid empirical studies analyzing the effects of rewards in MOOC environments. This paper reports a between-subjects design study conducted in a MOOC to analyze the effects of badges and redeemable rewards on student retention and engagement. Results show that the implemented reward strategies had not significant effect on student retention and behavioral engagement measured through the number of pageviews, task submissions, and student activity time. However, it was found that learners able to earn badges and redeemable rewards participated more in gamified tasks than those learners in the control group. Additionally, results reveal that the participants in the redeemable reward condition requested and earned earlier the rewards than those participants in the badge condition. The potential implications of these findings in the instructional design of future gamified MOOCs are also discussed.Ministerio de Ciencia, Innovación y Universidades (projects TIN2017-85179-C3-2-R / TIN2014-53199-C3-2-R)Junta de Castilla y León (project VA257P18)European Commission (project 588438-EPP-1-2017-1-EL- EPPKA2-KA

From face-to-face to distance LMS-mediated collaborative learning situations with GLUE!

GLUE! is an integration architecture that allows teachers to easily set up an LMS environment with several external tools to carry out complex collaborative learning situations in distance settings. Though its effectiveness in alleviating the burden on teachers of deploying and enacting such situations has been studied elsewhere, there are no studies in the literature analyzing the impact, in terms of learning achievement, of turning traditional face-to-face collaborative learning situations into distance LMS-mediated ones with the support of integration approaches such as the GLUE! architecture. This paper compares the learning achievement in a distance LMS-mediated collaborative learning situation supported by GLUE! and in the equivalent face-to-face in a non-technological setting. The conclusions of this comparison, along with the fact that GLUE! significantly reduces the set up effort, suggest that GLUE! is a good choice for turning traditional face-to-face collaborative learning situations into distance LMS-mediated ones without significant negative effects in the learning achievement.This work has been funded by the Spanish Ministry of Economy and Competitiveness projects TIN2011-28308-C03-01 andTIN2011-28308-C03-02, and the postdoctoral fellowship Alliance 4 Universities.Publicad