Study on the effectiveness of commercial anti‐islanding algorithms in the prospect of mass penetration of PVs in low‐voltage distribution networks

In the coming years, distribution grids will be progressively flooded by renewable energy sources (RES) that will be interconnected with the main grid through power electronic converters. Photovoltaics (PVs) are one of the most promising renewable technologies even for densely built-up areas where space problems are inevitable. The high penetration prospect of PV facilities on low-voltage distribution networks raises questions regarding the necessity of advanced functions that will enable electronically coupled RES to support the operation of distribution grids and to enhance their reliability. In this context, the objective of this study is to investigate the effectiveness of various islanding prevention measures installed in commercial PV inverters, when multiple inverters are operating in parallel with a low-voltage distribution network (LVDN). Extensive experiments were performed under various PV penetration levels, linear/non-linear load and over/under voltage and over/under frequency conditions, as well as for various values of total harmonic distortion of the mains voltage. Further to the primary statistical analysis, the results were analysed in depth by advanced mathematical methods such as box plot and cluster analysis. The findings of this study indicate that commercial anti-islanding techniques present a high probability of failure in the case of multiple PV units at the same point of common coupling, calling for new and more advanced algorithms.European Commission, H2020, 65411

Evaluation of performance at experimental buildings and real demonstration sites in BFIRST project: Theoretical and practical aspects for BIPV monitoring system

Monitoring is one of the main activity of BFIRST, Building-integrated FIbre-Reinforced Solar Technology, project, a 5 years funded European project, project reference number 29601, that started in April 2102 and deals with the design, development and demonstration of a portfolio of innovative photovoltaic products for building integration, based on cell encapsulation within fibre-reinforced composite materials. Automatic data acquisition systems are generally required for monitoring, performance evaluation and exchanging data of PV systems. Standard IEC 61724:1998 “Photovoltaic system performance monitoring –Guidelines for measurement, data exchange and analysis” provides a guideline that shall be followed in these cases. As far as Building Integrated Photovoltaics (BIPV) are considered, besides electrical parameters there is in addition the need to monitor the specific building performances. That is because a BIPV module operates as a multi-functional building construction material; it generates energy and serves as part of the building envelope. Since the building related performances are not included in the aforementioned IEC standard, a general guideline for monitoring was prepared within the project that has been used within the project at two levels: one at experimental sites mainly related to experimental single module testing and the other at demosite with real PV size plants

Optimum design of a high frequency single phase inverter for the interconnection of small power PV systems with the low voltage network

The scope of the present work is to contribute in the sector of the Dispersed Power Generation PV systems with the development of an inverter that will be used for the interconnection of small PV generators with the electric network of urban regions. In more details the development of an inverter with electrical isolation is investigated which on the one hand it will ensure high power factor regulation and high efficiency for wide power range and on the other hand it will be characterised by simple power electronic circuit structure in order to ensure high reliability. Moreover, particular characteristics of this inverter should be the small volume and the small weight attributes very important considering its applications (incorporation in PV generators that will be placed in aspects or roofs of buildings). The interest of present work is focused in the high frequency current source Flyback inverter. For this topology two different control techniques were investigated leading to different operation modes. Moreover, their suitability is studied for different power levels. For both control techniques mathematic models were developed connecting the transferred power in the public grid with the inverter operational parameters as well as criteria for the inverter safe operation area were exported considering the acceptable peak voltage and current values for the semiconductor switches. Moreover, the combined application of two control techniques is proposed and an optimum inverter design strategy is presented aiming to the development of an inverter with the smallest possible volume as well as to the achievement of high power factor regulation and high efficiency for wide power range Last but not least a current pulsation smoothing active filter is investigated and developed which permits the elimination of the low frequency inverter input current. The current pulsation is a result of the power pulsation due to the single phase power generation and its elimination is of great importance in order to exploit the maximum PV generated electricity power. The active filter configuration is independent from the inverter topology and its operation mode and hence it can be applied for various single stage topologies. The precision of the mathematic models the correctness of the proposed design strategy and the effectiveness of the proposed active filter are validated via simulation and experimental results. Finally, the conclusions of whole study are exhibited.Σκοπός της παρούσας εργασίας είναι η συμβολή της στον τομέα των φωτοβολταϊκών μονάδων διεσπαρμένης παράγωγης με την αναζήτηση μιας διάταξης διασύνδεσης Φ/Β γεννητριών μικρής ισχύος με το ηλεκτρικό δίκτυο των αστικών περιοχών. Συγκεκριμένα διερευνάται η δυνατότητα ανάπτυξης μιας ηλεκτρονικής διάταξης με απομόνωση η οποία αφ’ ενός μεν θα εξασφαλίζει υψηλό συντελεστή ισχύος και υψηλό βαθμό απόδοσης για ευρύ φάσμα λειτουργίας αφ’ ετέρου δε θα διέπεται από μικρό βαθμό πολυπλοκότητας στο κύκλωμα ισχύος της προκείμενου να εξασφαλίζεται υψηλή αξιοπιστία. Το ενδιαφέρον της εργασίας εστιάσθηκε στον υψίσυχνο αντιστροφέα ρεύματος τοπολογίας Flyback. Για τη διάταξη αυτή διερευνήθηκαν δύο διαφορετικές τεχνικές ελέγχου (οι οποίες οδηγούν σε διαφορετικές καταστάσεις λειτουργίας) και ελέγχθηκε η καταλληλότητά τους για διαφορετικά επίπεδα ισχύος. Για τις δυο αυτές τεχνικές ελέγχου αναπτύχθηκαν μαθηματικά μοντέλα που συνδέουν τη μεταφερομένη στο δίκτυο ισχύ με τις κατασκευαστικές παραμέτρους του αντιστροφέα και εξήχθησαν κριτήρια για τα ασφαλή όρια λειτουργίας του αντιστροφέα με γνώμονα την καταπόνηση των ημιαγωγικών στοιχείων ισχύος. Επιπλέον, προτάθηκε η συνδυασμένη εφαρμογή των δύο τεχνικών ελέγχου και παρουσιάστηκε μια στρατηγική σχεδιασμού του αντιστροφέα ώστε να γίνεται βέλτιστη επιλογή όλων των επιμέρους λειτουργικών του στοιχείων με ταυτόχρονη ελαχιστοποίηση του όγκου του, επίτευξη υψηλού συντελεστή ισχύος καθώς και υψηλού βαθμού απόδοσης για ευρύ φάσμα της παραγόμενης ισχύος. Τέλος, διερευνήθηκε η δυνατότητα ανάπτυξης ενός ενεργού φίλτρου για την αποτελεσματική εξομάλυνση της έντονης κυμάτωσης του ρεύματος εισόδου του προτεινομένου αντιστροφέα. Η κυμάτωση αυτή είναι αποτέλεσμα της τροφοδότησης του μονοφασικού ηλεκτρικού δικτύου Ε.Ρ. από τη συνεχή τάση και το συνεχές ρεύμα που παράγουν οι φωτογεννήτριες και ο περιορισμός της είναι ιδιάζουσας σημασίας προκείμενου να καταστεί δυνατή η αποδοτική λειτουργία της όλης διάταξης. Η λειτουργία του προτεινομένου ενεργού φίλτρου είναι ανεξάρτητη τόσο των καταστάσεων λειτουργίας του αντιστροφέα τύπου Flyback όσο και γενικότερα της τοπολογίας του αντιστροφέα καθιστώντας την έτσι ως μια ελκυστική λύση και για διαφορετικές τοπολογίες μετατροπέων. Η ακρίβεια των μαθηματικών μοντέλων, η ορθότητα της προτεινομένης στρατηγικής σχεδιασμού και η αποτελεσματικότητα του προτεινομένου ενεργού φίλτρου επιβεβαιώθηκαν μέσω προσομοίωσης και πειραματικών δοκιμών ενώ τέλος παρατίθενται τα συμπεράσματα από το σύνολο της εργασίας

On the Implementation of the Nearly Zero Energy Building Concept for Jointly Acting Renewables Self-Consumers in Mediterranean Climate Conditions

Cost-effective energy saving in the building sector is a high priority in Europe; The European Union has set ambitious targets for buildings’ energy performance in order to convert old energy-intensive ones into nearly zero energy buildings (nZEBs). This study focuses on the implementation of a collective self-consumption nZEB concept in Mediterranean climate conditions, considering a typical multi-family building (or apartment block) in the urban environment. The aggregated use of PVs, geothermal and energy storage systems allow the self-production and self-consumption of energy, in a way that the independence from fossil fuels and the reliability of the electricity grid are enhanced. The proposed nZEB implementation scheme will be analyzed from techno-economical perspective, presenting detailed calculations regarding the components dimensioning and costs-giving emphasis on life cycle cost analysis (LCCA) indexes—as well as the energy transactions between the building and the electricity grid. The main outcomes of this work are that the proposed nZEB implementation is a sustainable solution for the Mediterranean area, whereas the incorporation of electrical energy storage units—though beneficial for the reliability of the grid—calls for the implementation of positive policies regarding the reduction of their payback period

On the exploitation of dynamic simulations for the design of buildings energy systems

To achieve the Paris Agreement 1.5 °C target, apart from the obligation for new buildings to be ZEBs, the existing building stock should be retrofitted as well, in order to improve their energy efficiency by using more efficient electromechanical energy systems and envelope materials, whereas RES should cover their energy needs. In this context, Energy Performance Certificates (EPCs) have been institutionalized to certify the energy behavior of buildings. Various types of buildings energy modeling tools and calculation methods have been proposed for EPCs procedures. This study focuses on the energy performance gap between dynamic and quasi steady-state simulation tools. The results from a comparative case study have shown remarkable discrepancies between dynamic and quasi-steady-state simulation processes, for the same building. Indeed, the quasi-steady-state simulation tool estimates 4.5% higher annual electricity consumption per conditioned area for the existing building and approximately 74% less energy savings for the retrofitted one, leading to an overestimation of 85% in CO2 emissions prediction. Finally, compared to the analysis with the dynamic simulation tool, an increased retrofit cost, approximately by 19.7% (and thus 3 times higher payback period), is needed according to the results of the quasi-steady-state simulation tool, in order to achieve the same Energy classification

Enhanced nZEB concept incorporating a sustainable Grid Support Scheme

The building sector in Europe represents a large amount of the total energy consumption. European Union policies urge energy management systems installation in buildings, to achieve the nZEB targets and mitigate the climate change. Except for renewable energy sources, the incorporation of energy storage units (ESUs) is of major importance for building energy management, in order to increase self-consumption levels. The present work contributes to the mass installation of ESUs in building sector, as a tool to provide flexibility in the distributed production of energy. This concept is an enhanced version of nZEBs that is able to compete in the Electricity Market, and to contribute to the reliability and flexibility of the electricity grid as an alternative to centralized ESUs investments. In this context, the present work proposes a new type of grid ancillary services for building sector and a novel Grid Support Scheme (GSS) that considers both the energy fluctuations of the available energy in the ESU as well as the energy transactions with the grid. The proposed GSS model concludes to a pricing policy relying on the Value of Lost Load (VoLL), in order that the proposed grid support investment becomes sustainable. The validation of the GSS is performed by means of Life Cycle Cost Assessment

Current Trends in Electric Vehicle Charging Infrastructure; Opportunities and Challenges in Wireless Charging Integration

Nowadays, the imperative need for the reduction of Greenhouse Gas (GHG) emissions leads to the wider adoption of environmentally friendly transportation means. As a result, various policies underpinning the Electric Vehicle (EV) deployment are legislated globally, and several technical advances contributing to the electrification of the transportation sector are pursued. In this paper, a comprehensive overview of the current status of the infrastructure utilized for the realization of both conductive and contactless (wireless) charging of an EV battery is conducted. Furthermore, the issue of EV integration in conventional distribution networks, as well as in future power system architectures, is discussed in detail. Particular focus is given to wireless (i.e., inductive) charging. A detailed presentation of the respective standards and charging levels, as well as the magnetic couplers and the compensation network configurations, is carried out. Moreover, innovative concepts such as dynamic and quasi-dynamic wireless charging, as well as future challenges and opportunities, are presented and discussed. Finally, smart control and communication techniques applicable to EV charging are presented in the context of the future Internet of Energy (IoE) concept

Energy investigation on households with BIPV modules under net metering scheme

In recent years many Renewable Energy Sources (RES) power plants have been connected to power networks throughout Europe, in order to meet the EU’s objectives for sustainable energy supply. As far as low-voltage distribution networks are concerned, the grid-connected photovoltaic (PV) systems constitute the most important representative of RES, because these can be easily installed even in densely built-up areas where space problems are inevitable. In this context, small residential PV systems utilising BIPV modules are going to gain ground mainly at newly built or rebuilt building structures. That is because a BIPV module operates as a multi-functional building construction material; it generates energy and serves as part of the building envelope. This paper highlights the energy benefits of residential buildings in Southern Europe with BIPV modules under Net Metering Scheme. The energy benefits are reflected in monthly basis

Detecting Parkinsonian Tremor from IMU Data Collected In-The-Wild using Deep Multiple-Instance Learning

Parkinson's Disease (PD) is a slowly evolving neuro-logical disease that affects about 1% of the population above 60 years old, causing symptoms that are subtle at first, but whose intensity increases as the disease progresses. Automated detection of these symptoms could offer clues as to the early onset of the disease, thus improving the expected clinical outcomes of the patients via appropriately targeted interventions. This potential has led many researchers to develop methods that use widely available sensors to measure and quantify the presence of PD symptoms such as tremor, rigidity and braykinesia. However, most of these approaches operate under controlled settings, such as in lab or at home, thus limiting their applicability under free-living conditions. In this work, we present a method for automatically identifying tremorous episodes related to PD, based on IMU signals captured via a smartphone device. We propose a Multiple-Instance Learning approach, wherein a subject is represented as an unordered bag of accelerometer signal segments and a single, expert-provided, tremor annotation. Our method combines deep feature learning with a learnable pooling stage that is able to identify key instances within the subject bag, while still being trainable end-to-end. We validate our algorithm on a newly introduced dataset of 45 subjects, containing accelerometer signals collected entirely in-the-wild. The good classification performance obtained in the conducted experiments suggests that the proposed method can efficiently navigate the noisy environment of in-the-wild recordings