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Includes bibliographical references. Number of sources in the bibliography: 142 Thesis (Ph. D.) -- University of Cyprus, Faculty of Engineering, Department of Electrical and Computer Engineering, 2020. The University of Cyprus Library holds the printed form of the thesis. Καθώς τα συστήματα ηλεκτρικής ισχύος προχωρούν προς την υλοποίηση των “ευφυών δικτύων”, καινούριες προκλήσεις εμφανίζονται λόγω των μεγάλων αλλαγών που υπόκεινται τα δίκτυα αυτά. Μία από τις μεγαλύτερες προκλήσεις που καλούνται τα συστήματα ηλεκτροδότησης να αντιμετωπίσουν είναι η εμφάνιση διαταραχών μεταξύ περιοχών του δικτύου. Οι διαταραχές αυτές προκύπτουν ουσιαστικά από την αδύνατη διασύνδεση διαφορετικών περιοχών του συστήματος, όπου οι συμβατικές μέθοδοι ελέγχου αποτυγχάνουν στην εξ’ ολοκλήρου απόσβεσή τους. Αυτό συμβαίνει κυρίως λόγω της ανεπαρκούς πληροφόρησης για την κατάσταση ολόκληρου του συστήματος και της χρήσης μόνο τοπικών σημάτων. Η ικανότητα παρατήρησης αυτών των διαταραχών κατέστη δυνατή μόνο μετά την εμφάνιση των Μετρητών Φασιθετών στα συστήματα ηλεκτρικής ισχύος. Οι συσκευές αυτές έχουν τη δυνατότητα παροχής συγχρονισμένων μετρήσεων σε σχεδόν πραγματικό χρόνο, συμβάλλοντας καθοριστικά στην υλοποίηση συστημάτων παρατήρησης και ελέγχου ευρείας περιοχής. Ο σκοπός του ελέγχου ευρείας περιοχής (ΕΕΠ) είναι να χρησιμοποιήσει με τέτοιο τρόπο τις συγχρονισμένες μετρήσεις, ώστε να εξαγάγει σήματα ανάδρασης με σκοπό την επιτυχή και πλήρης εξάλειψη όλων των διαταραχών μεταξύ των περιοχών. Ως εκ τούτου η ανάγκη για δημιουργία και χρήση ΕΕΠ υψηλής επίδοσης έχει γίνει εμφανής τα τελευταία χρόνια.Παρόλα αυτά, το κοινό πρόβλημα το οποίο παρατηρείται σε υφιστάμενες μεθόδους σχεδιασμού ΕΕΠ, είναι η παράλειψη της δημιουργίας εύρωστων ελεγκτών οι οποίοι θα μπορούν να έχουν υψηλή επίδοση σε διάφορες συνθήκες που μπορούν να προκύψουν. Επίσης, αγνοείται σχεδόν παντελώς το γεγονός ότι το σύστημα δεν λειτουργεί σε ιδανικές συνθήκες, ότι νέα δυναμικά στοιχεία εμφανίζονται συνεχώς στο σύστημα, καθώς και το ότι υπάρχουν αβεβαιότητες στις παραμέτρους του συστήματος οι οποίες χρησιμοποιούνται από τον διαχειριστή του συστήματος. Ως εκ τούτου, η συγκεκριμένη διδακτορική διατριβή έχει ως πρωταρχικό στόχο την ανίχνευση και επιτυχή αντιμετώπιση των σημαντικών παραγόντων που μπορούν να επηρεάσουν την λειτουργία του ΕΕΠ. Η επίτευξη αυτού του στόχου κατέστη δυνατή με την δημιουργία ρεαλιστικών προσομοιώσεων οι οποίες είναι ιδιαίτερα αναλυτικές κατά την διάρκεια δυναμικών συνθήκων και παρέχουν ένα περιβάλλον κατάλληλο για δοκιμή της επίδοσης του ΕΕΠ. Στη συγκεκριμένη διδακτορική διατριβή, ο ΕΕΠ δοκιμάστηκε κάτω από διάφορες συνθήκες όπως σφάλματα στις μετρήσεις, καθυστέρηση και απόρριψη δεδομένων, ύπαρξη αβεβαιότητας στις αποθηκευμένες παραμέτρους των γραμμών και των γεννητριών του συστήματος, μη αναφορά τοπολογικών αλλαγών του συστήματος και ύπαρξη δυναμικών φορτίων. Το αποτέλεσμα της έρευνας έδειξε ότι η λειτουργία του ΕΕΠ επηρεάζεται από την καθυστέρηση και απόρριψη δεδομένων, τη μη αναφορά τοπολογικών αλλαγών του συστήματος καθώς και από την ύπαρξη δυναμικών φορτίων στο σύστημα. Επιπλέον, η συνεχής εισδοχή Ανανεώσιμων Πηγών Ενέργειας (ΑΠΕ) στο δίκτυο αποτελεί έναν από τους πιο γνωστούς παράγοντες που μπορούν να επηρεάσουν την ευστάθεια του συστήματος και επομένως είναι ένα παράγοντας ο οποίος επίσης πρέπει να αντιμετωπιστεί. Η διδακτορική διατριβή αυτή παρουσιάζει μεθοδολογίες για την επιτυχή αντιμετώπιση όλων των θεμάτων. Συγκεκριμένα, για να αποφευχθεί η καθυστέρηση και η απόρριψη δεδομένων, έχουν υλοποιηθεί γρήγορες μέθοδοι γραμμικής πρόβλεψης οι οποίες διατηρούν υψηλή την ακρίβεια του ΕΕΠ ακόμα και σε μεγάλες καθυστερήσεις. Στην περίπτωση των ΑΠΕ, μια καινούρια μεθοδολογία ΕΕΠ ιεραρχικής διαβάθμισης έχει προταθεί σε αυτή την διατριβή, για τον επιτυχή συντονισμό όλων των γεννητριών και ΑΠΕ με σκοπό την πλήρης εξουδετέρωση όλων των διαταραχών. Η ύπαρξη άγνωστων τοπολογικών αλλαγών επιλύθηκε με την συνένωση της Παρατήρησης Ευρείας Περιοχής (ΠΕΠ) μαζί με τον ΕΕΠ η οποία υλοποιήθηκε μέσα σε προσομοιωτές πραγματικού χρόνου. Οι επιπτώσεις της ύπαρξης δυναμικών φορτίων, αντιμετωπίστηκαν μέσω της κατασκευής και χρήσης ΕΕΠ υψηλής επίδοσης. Τέλος, μειονεκτήματα της αρχικής μεθόδου που χρησιμοποιήθηκε έχουν εντοπιστεί και επιλυθεί κατάλληλα.Ο δεύτερος στόχος της διδακτορικής διατριβής είναι η υλοποίηση προχωρημένων και καινοτόμων μεθόδων ΕΕΠ. Οι εν λόγω μέθοδοι κατασκευάστηκαν χρησιμοποιώντας ρεαλιστικές προσομοιώσεις πραγματικού χρόνου για μεγαλύτερη ακρίβεια καθώς και για δοκιμή σε σχεδόν πραγματικές συνθήκες. Στόχος των καινοτόμων μεθοδολογιών είναι ο σωστός και επιτυχής συντονισμός της λειτουργίας των τοπικών ελεγκτών όλων των γεννητριών. Πιο συγκεκριμένα, καινοτόμες μέθοδοι ΕΕΠ δημιουργήθηκαν με σκοπό τον καλύτερο έλεγχο του ρυθμιστή στροφών, του συστήματος διεγέρσεως και του σταθεροποιητή, ελέγχοντάς τους με τα κατάλληλα σήματα έτσι ώστε να μπορούν να αντιμετωπίσουν επιτυχώς όλες τις τοπικές διαταραχές αλλά και όλες τις διαταραχές μεταξύ των περιοχών του συστήματος. Η σύγκριση των προτεινόμενων μεθόδων με αντίστοιχες συμβατικές πραγματοποιήθηκε χρησιμοποιώντας την μέθοδο Prony. Επίσης, στα πλαίσια αυτής της διδακτορικής διατριβής, μια προχωρημένη μέθοδος για τον προσαρμοστικό έλεγχο των τοπικών ελεγκτών από τον ΕΕΠ έχει προταθεί. Η συνένωση όλων των καινοτόμων μεθόδων οδηγεί στην εμφάνιση ενός προχωρημένου ελεγκτή ευρείας περιοχής ο οποίος παρέχει υψηλή επίδοση κυρίως για την εξάλειψη όλων των διαταραχών μεταξύ περιοχών, ενισχύοντας έτσι σημαντικά την ευστάθεια του συστήματος ηλεκτρικής ισχύος ακόμα και σε ακραίες συνθήκες. Inter-area oscillations have become one of the major challenges that modern power systems have to confront, since their appearance is increasing due to the vast changes and constant expansion of the power systems. The appearance of inter-area oscillations creates many issues such as the degradation of the power quality, the limitation of the transmission system capacity and in several occasions, it can even lead the system to instability. Typical local controllers utilized for damping any undesirable oscillations, fail to compensate them due to the lack of global observability. The utilization of Phasor Measurement Units (PMUs) into the power systems and the provision of synchronized measurements has made possible the observation of inter-area oscillations. Wide Area Control (WAC) aims to utilize effectively the near real-time information provided by the PMUs in order to provide feedback control and coordination signals to the system, having as an objective the compensation of all the inter-area oscillations along with the enhancement of the system’s damping performance. Therefore, the necessity for the successful development of highly effective wide area controllers is becoming more apparent recently. However, an aspect which is commonly disregarded during the WAC design phase is that the robustness of the wide area controller has to be ensured and must not be compromised under any conditions. In addition to this, the simulated conditions, usually utilized for the evaluation of the WAC performance, do not consider that the system is not ideal, it almost never operates in steady-state conditions, new dynamic components are making their appearance into the grid and that there are uncertainties considering known parameters of the system. Therefore, the first objective of this Ph.D. dissertation is to identify the most crucial factors which can affect the WAC operation and then propose methods to mitigate their effect, having as a goal to obtain a highly robust wide area controller. The former was made possible by developing realistic simulation environments (especially when dynamic conditions take place), suitable for testing WAC methodologies. The performance of the wide area controller was tested under the presence of measurement errors (steady-state and dynamic), data delays/dropout, system parameter uncertainties (transmission line and generator data), unreported topology changes and dynamic loads. The investigation revealed that the WAC performance is mainly affected from the data delays/dropout, the unreported topology changes and the presence of dynamic loads. Apart from these, a widely known reason for the degradation of the system stability is the increasing penetration of the Renewable Energy Sources (RESs), since they reduce the system’s inertia and change its dynamic characteristics. This Ph.D. dissertation proposes methods for the compensation of all the identified threads. Considering the data delays/dropout, fast model-free linear predictors are developed, which improve considerably the damping performance of the system even at the presence of severe delays. For the case of the renewables, a novel wide area controller is introduced which is able to utilize and coordinate appropriately both synchronous generators and RESs, enhancing that way the damping performance of the system, even under a high penetration of renewables. In order to mitigate the effect of the unreported topology changes, a combination of Wide Area Monitoring (WAM) and WAC schemes is developed in a real-time simulation environment, while the impact of the dynamic loads is addressed by implementing high performance coordination methods. Apart from the identified threats, drawbacks of the conventional controller are addressed as well in order to enhance significantly its robustness. The second objective of this Ph.D. dissertation is the development of a highly effective wide area controller, by proposing novel coordination techniques. These methodologies are implemented and tested in real-time conditions (through a real-time simulator) which in combination with the aforementioned realistic simulation environments can result into the most suitable testbed for testing and validating WAC methods. Therefore, advanced schemes are proposed for the proper coordination of the synchronous generator local controllers, which are evaluated by comparing their performance to conventional methods through Prony analysis. More specifically, novel techniques are developed for enhancing the operation of the exciter, the governor and power system stabilizer (PSS). It should be noted that for the case of the governor and PSS coordination, a methodology is implemented which can be used either in coordinating all the governors of the system or in coordinating simultaneously both the governor and PSS of each generator through a common WAC signal. Furthermore, an adaptive tuning method for regulating adaptively the level of the WAC contribution to all the local controllers is also developed and applied to the novel coordination techniques in order to enhance even more their performance. The combination of all the advanced methodologies along with the application of the adaptive tuning method result to the appearance of an advanced wide area controller, which has high performance in damping effectively all the local and inter-area oscillations even under extreme conditions (i.e. high penetration of dynamic loads). The integration of the advanced wide area controller with the WAM application is realized and evaluated in almost actual conditions, through the utilization of a novel laboratory setup.

The integration of modern renewable energy sources is enabled by the grid side converter (GSC) based on power electronic technology. The operation of the GSC is properly regulated by the GSC controller according to sensor measurements (i.e., of the grid voltage, of the line currents, and of the voltage at the dc-link). However, in case of current sensor faults, the operation of the GSC and of the entire renewable system can be critically affected and catastrophic failures may occur if the sensor fault is not accommodated on time. This paper proposes a model-based Fault Detection, Isolation, and Accommodation (FDIA) scheme, which enables the GSC to overcome faults that may occur on the associated current sensors. The sensor fault detection and isolation scheme has been designed based on analytical redundancy relations, while the accommodation of the faults is based on an adaptive estimation scheme. The proposed FDIA scheme has been applied on a modern GSC and the effectiveness of the scheme has been tested under several multiple current sensor faults and under several grid conditions. Furthermore, the FDIA scheme enables the GSC to operate properly (without causing failures or damages to its components) under current sensor faults and thus, the reliability of the GSC is enhanced.

Synchronization is a crucial aspect in grid-tied systems, including single-phase photovoltaic inverters, and it can affect the overall performance of the system. Among prior-art synchronization schemes, the Multi Harmonic Decoupling Cell Phase-Locked Loop (MHDC-PLL) presents a fast response under grid disturbances and high accuracy under harmonic distortions. However, major drawbacks of the MHDC-PLL include increased complexity and inaccurate response under non-nominal frequencies, which may occur in practical applications. Thus, this paper proposes strategies to address these issues. At first, a novel re-formulation of an equivalent decoupling cell is proposed for reducing the implementation complexity, and then a frequency adaptive quadrature signal generator for the MHDC-PLL is proposed to enable an accurate response even under non-nominal frequencies. Simulation and experimental results are provided, which show that the proposed synchronization (i.e., the frequency adaptive MHDC-PLL) can achieve a fast and accurate response under any grid disturbance and/or severe harmonic conditions., This work was supported by the Research Promotion Foundation of Cyprus (RPF, Cyprus, Project KOINA/SOLAR-ERA.NET/0114/02), by Energinet.dk (ForskEL, Denmark) and the SOLAR-ERA.NET (European Union's Seventh Framework Programme). © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. L. Hadjidemetriou, Y. Yang, E. Kyriakides and F. Blaabjerg, "A synchronization scheme for single-phase grid-tied inverters under harmonic distortion and grid disturbances," IEEE Trans. Power Electronics, vol. 32, no. 4, pp. 2784-2793, April 2017. DOI: 10.1109/TPEL.2016.2581019. https://www.ieee.org/publications_standards/publications/rights/rights_policies.html

An Intentional Controlled Islanding (ICI) algorithm that directly determines an islanding solution with minimal power-flowdisruption for any given number of islands, while ensuring that each island contains only coherent generators was previouslyproposed and tested using IEEE test systems. The proposed algorithm is based on an exact Mixed Integer LinearProgramming Formulation (MILP). However, since voltage instability has been found to be one of the main causes of severalrecent blackouts in the world, in this paper, the aforementioned algorithm is extended to consider voltage stability constraints.The extended ICI algorithm guarantees sufficient generation capacity (active and reactive power) to match the loadconsumption within each island. At the same time, it reduces the possibility of voltage collapse by assigning the weakest buses to the islands in such a way to be as close as possible to the sources or sinks of reactive power. The new constraints areexpected to further improve the transient stability of the formed islands.

Grid-scale Battery Energy Storage Systems(BESSs) are gaining increasing consideration over the last fewyears since their connection has been shown to improve thedynamic behavior of the power grid. However, existingIntentional Controlled Islanding (ICI) approaches do notconsider the changes in structure and operation that modernpower systems are experiencing due to the increasing integrationof grid-scale BESSs. In this paper a previously proposed ICIalgorithm (for minimal power-flow disruption) is modified toconsider the impact of BESSs on the power system. Morespecifically, the proposed modified ICI algorithm aims todetermine the optimal islanding solution that minimizes thepower imbalance between the generation (i.e., synchronousgenerators and the BESSs) and the consumption (i.e., loads andBESSs) within each island. This is achieved through determiningthe island that each BESS should be, and the optimal activepower set-points for the BESSs that minimize the powerimbalance in the formed islands.

Microgrids composed of solemnly AC-coupled distributed energy resources can be found in many real-life applications while their control has not been researched nearly enough to address some fundamental challenges, the most important of which is overall system reliability and fault tolerance. This paper proposes a droop-based coordinated control scheme for microgrids with AC-coupled units, a method that enables distributed energy resources units to hot swap between current source and voltage source grid-supporting control modes for satisfying load demand and ensuring energy storage systems will constantly be able to form the grid during islanded operation. The proposed control scheme has been realised in MATLAB/Simulink simulation model of a small-scale microgrid of AC-coupled units that corresponds to a real testbed in Northern Greece. Preliminary simulation results, in islanded mode, demonstrate the effectiveness of the proposed control scheme regarding power-sharing accuracy among the resources and state-of-charge balancing among storage units. 1 6

Power system operators are facing major challenges today to keep the system operating at the admissible limits. Recent blackouts demonstrated the need for a systematic study and design of a comprehensive system control strategy. Intentional controlled islanding (ICI) has been proposed as an effective corrective control action of final resort to save the system from a partial or a complete blackout. ICI limits the occurrence and consequences of blackouts by splitting the power system into a group of smaller, stable, and sustainable subsystems, also called islands. After a controlled system separation, power system operators should resynchronize and reconnect each island to restore the system. In this sense, real-time knowledge of the operating condition of the islands is required. In this paper, a real-time ICI and restoration scheme is proposed. The proposed scheme consists of an ICI algorithm that finds islanding solutions with minimal power-flow disruption while considering power system restoration constraints (e.g., blackstart availability, sufficient generation capacity, and observability), a real-time state estimator that monitors the system before and after the islanding, and a restoration process. The proposed ICI and restoration scheme is tested using the dynamic IEEE 39- and 118-bus test systems. 34 1 606 615

This paper presents an optimal scheduling for the utilization of the battery energy in order to minimize the cost of the electricity bill in a non-residential building equipped with a photovoltaic-storage system. The battery storage device is connected at the DC-link of the photovoltaic system for enabling a more efficient grid integration through a common central inverter. For the optimal scheduling method, the day-ahead electricity pricing and the next-day forecasted building load and PV generation for each quarter hour are taken into consideration. The problem is formulated as a mixed-integer linear programming model and is solved using commercial solvers. Furthermore, the efficiency curve of the inverter is approximated by a discretized step function and along with the battery efficiency are included in the formulation. Two case studies are carried out using real data and useful results according to the energy flow in the system and the profit are obtained.

Includes bibliographical references (p. 82-88). Number of sources in the bibliography: 74 Thesis (Ph. D.) -- University of Cyprus, Faculty of Pure and Applied Sciences, Department of Computer Science, 2018. The University of Cyprus Library holds the printed form of the thesis Στα σύγχρονα συστήματα ηλεκτρικής ενέργειας χρησιμοποιούνται ως επί το πλείστον συμβατικά σχήματα αποκοπής φορτίου σε περιπτώσεις όπου υπάρχει έλλειμα παραγωγής. Αυτά τα συμβατικά σχήματα χρησιμοποιούν μια αρχιτεκτονική που βασίζεται στη βηματική αποκοπή φορτίου προκειμένου να επιτευχθεί η διατήρηση της συχνότητας του ηλεκτρικού δικτύου σε επιθυμητά επίπεδα σε περιπτώσεις σοβαρής έκτακτης ανάγκης (π.χ., μαζική απώλεια παραγωγής). Υπάρχουν προκαθορισμένα υποψήφια προς αποκοπή κυκλώματα που βασίζονται στη σημαντικότητά τους, τα ιστορικά δεδομένα, τη ζήτηση ηλεκτρικής ισχύος σε κάθε υποσταθμό και την εμπειρία του διαχειριστή του συστήματος. Οι συνθήκες κάτω από τις οποίες συμβαίνει κάποιο σφάλμα ή μια βλάβη διαφέρουν και έχουν ως αποτέλεσμα την αποκοπή μικρότερης ή μεγαλύτερης ποσότητας ηλεκτρικού φορτίου από την απαιτούμενη και συνεπώς στη μη-βέλτιστη λειτουργία του σχήματος αποκοπής φορτίου. Επιπρόσθετα, τα πρόσφατα προτεινόμενα ημί-προσαρμοστικά σχήματα αποκοπής φορτίου είναι λειτουργικά μόνο στη θεωρία μια και για να λειτουργήσουν ικανοποιητικά στην πράξη χρειάζονται μεγάλο αριθμού δεδομένων συλλεχθέντων σε πραγματικό χρόνο. Αυτά τα δεδομένα δεν μπορούν εύκολα να συλλεγούν σε μεγάλη κλίματα και με τρόπο αποδοτικό από οικονομικής άποψης. Επιπλέον, τα προηγούμενα προταθέντα σχήματα αποκοπής φορτίου αποτυγχάνουν να ανταποκριθούν με επάρκεια σε πρωτόγνωρα ή συνδιαστικά συμβάντα, είναι συντηρητικά ως προς την ποσότητα του φορτίου που πρέπει να αποκοπεί και δεν καταπιάνονται με την επιλεκτική διάσταση του φαινομένου της αποκοπής φορτίου. Σ’ αυτή την διδακτορική διατριβή, προτείνεται αριθμός από καινοφανή σχήματα αποκοπής φορτίου (βασιζόμενα σε μοντέλο, πλήρως προσαρμοστικά και αναλυτικά), τα οποία ελαχιστοποιούν το συνολικό φορτίο που πρέπει να αποκοπεί και είναι εύρωστα σε διαδοχικές διαταραχές. Προσθετικά, οι επιπτώσεις του συνολικού χρόνου ανταπόκρισης των προτεινόμενων συστημάτων αποκοπής φορτίου σε σχέση με την ποσότητα του φορτίου προς αποκοπή έχουν μελετηθεί και ποσοτικοποιηθεί. Περαιτέρω, η παρούσα διδακτορική διατριβή μοντελοποιεί το ίχνος των σχημάτων αποκοπής φορτίου στην διάρκεια ζωής των περιστρεφόμενων μαζών του συστήματος ηλεκτρικής ενέργειας και παρέχει τη βέλτιστη ποσότητα φορτίου προς αποκοπή που εξασφαλίζει τη μέγιστη βιωσιμότητα από οικονομικής άποψης, λαμβάνοντας υπόψη το κόστος της μη εξυπηρετούμενης ενέργειας καθώς και το κόστος της μηχανικής καταπόνησης στην οποία υπόκεινται οι μονάδες ηλεκτροπαραγωγής. In contemporary power systems conventional Under Frequency Load Shedding (UFLS) schemes are typically used. These UFLS schemes employ a step-level structure to calculate the amount of load to be shed in the case of a severe contingency (e.g., massive loss of generation). There are pre-defined candidate circuit breakers to be opened, based on the importance of loads, historical data for the load demand at each substation, and the operator’s experience. However, real conditions at the time of fault differ, resulting to the shedding of a larger or smaller amount of load and to a non-optimal operation of the load shedding scheme. Furthermore, the recently proposed semi-adaptive load shedding schemes are usually only theoretically functional due to the large amount of real time monitoring data required to perform satisfactorily. These data cannot be obtained at a large scale and on a cost effective manner. Also, previously proposed UFLS schemes fail to respond adequately against newly emerging or combinational events, are conservative in terms of the amount of load to be shed and do not address the selectivity dimension as far as the combination of loads to be shed is concerned. In this Ph.D. thesis, a number of novel UFLS schemes are proposed (model based, fully adaptive and analytical) that minimize the total amount of UFLS and are robust to consecutive disturbances. Also, the impact of the total response time of the proposed UFLS schemes with regards to the load shedding amount was investigated and quantified. Additionally, this Ph.D. thesis models the footprint of the UFLS to the lifetime of the rotating equipment of the power system and provides the optimal amount of load shedding that ensures maximum sustainability from the economical point of view, taking into account the cost of unserved energy as well as the cost of the incurred fatigue of the generating units.

Recent decentralization of electricity systems together with the decarbonization and several changing societal demands are giving rise to different application scenarios such as microgrids. A microgrid is a small-scale electrical system which consists of several loads and sources (conventional and renewables) that can either operate autonomously in a stand-alone mode or interconnected with the main grid. The design and development of such a smart microgrid in a university campus is proposed within the 3DMicroGrid project (funded through the ERANETMED European Union’s initiative). This paper reviews the main components and characteristics of similar microgrids developed around the world. Furthermore, this study provides the design guidelines, the main functionalities, the key components and the control architecture for developing the microgrid proposed by the 3DMicroGrid project. A simulation model has been developed and initial results are demonstrated for the operation of this microgrid. The recommendations and insights are replicable to any solar priority country for future microgrids pilots.

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One of the main environmental targets of the European Union is to improve the energy efficiency in order to reduce the emissions of greenhouse gases. This work presents a cost-effective optimization method for design engineers to maximize the energy efficiency of electrical installations during the design phase. Hence, besides the safety and capacity requirements that need to be ensured during the design procedure of an electrical installation, the energy efficiency during its operation will also be considered. Thus, the proposed multi-objective optimization technique, based on genetic algorithms, offers a design guideline for the placement of the distribution boards, for the cable sizes and for the equipment used, for maximizing the energy efficiency of the building and at the same time the cost effectiveness of the electrical installation. The proposed method has been implemented and validated using a commercial software (Modecsoft ElectricalOM) for electrical installation designs.

During the last decade, microgrids are attracting a significant attention due to their numerous advantages. Amongst them, the most important one is their ability to operate either in grid-connected or in islanded (autonomous) mode. However, the transition between the two modes can be challenging in terms of maintaining the stability and integrity of the microgrid. In this paper, an optimization-based islanding methodology is developed to ensure a timely and smooth transition from the grid-connected to the islanded mode. This is achieved through shedding loads, by defining the generation level ofthe photovoltaics (energy spill) and by regulating the charging/discharging rate of batteries. A resynchronization method is also presented along with the requirements that need to be satisfied for the smooth reconnection of the microgrid back to the main grid. The effectiveness of the proposed approach is demonstrated through simulation results for the events of surplus energy production, and excess energy demand of the microgrid. 1 6

Power system transmission line parameters are essential in monitoring and control applications. More specifically, the values of the transmission line parameters are used in state estimation, contingency analysis, and as settings in protection relays. However, the stored transmission line parameters in the control center database often deviate from their actual values, impacting negatively the applications of the power system control center. The use of PMU (Phasor Measurement Unit) measurements is the most convenient and simple way for refining the parameters of the transmission line; however, the contamination of the PMU measurements with noise from the instrument transformers and the communication channels could sometimes deteriorate the accuracy of the calculated parameters. In this paper, the denoising of the PMU measurements using wavelets is proposed prior to the calculation of the transmission line parameters. The proposed approach is used for calculating the transmission line parameters of the IEEE 14-bus system and the results are extensively discussed.

Desalination of seawater and river water is a known technology with the capability of addressing the needs for clean and clear water. The process has a unique capability of storage which has a nexus to energy storage. The concomitant potential for system load factor improvement is discussed here, and the potential for favorable net present value of desalination plants is discussed. Application areas are also discussed. One conclusion is that desalination offers a real possibility for power marketing and this is especially attractive in view of the decline of electric energy sales in North America over the last eight years. As an example, a rough estimate of the electric energy requirement for California is given if 10% of statewide clean water is obtained by desalination. The paper also gives a brief overview of desalination internationally. 1 5

Intentional Controlled Islanding (ICI) has been proposed as a corrective measure of last resort to split the power system into several sustainable islands and prevent cascading outages. This paper proposes a novel ICI algorithm based on a Linear Programming (LP) formulation that directly determines an islanding solution with minimal power-flow disruption for any given number of islands, while ensuring that each island contains only coherent generators. In addition, the proposed algorithm enables operators to constrain any transmission line to be excluded from the solution, allows the control of the size of islands and ensures their connectivity. The basis of the proposed LP formulation is an exact Mixed Integer Linear Programming (MILP) Formulation. A Search Space Reduction (SSR) procedure that generates additional constraints for reducing the search space of the MILP is also proposed. In most cases, these additional constraints are enough for the relaxed MILP formulation (LP formulation) to generate optimal solutions. Nonetheless, the proposed LP formulation is executed as a part of a recursive linearization procedure which ensures that optimal solutions are always obtained. Multiple simulation results demonstrate the ability of the proposed LP ICI algorithm to meet the requirement of real-time controlled islanding in large-scale power systems., A. Kyriacou, P. Demetriou, C. Panayiotou and E. Kyriakides, "Controlled Islanding Solution for Large-Scale Power Systems," in IEEE Transactions on Power Systems, vol. 33, no. 2, pp. 1591 - 1602. doi: 10.1109/TPWRS.2017.2738326 © 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.

Includes bibliographical references (p. 143-151). Number of sources in the bibliography: 102 Thesis (Ph. D.) -- University of Cyprus, Faculty of Engineering, Department of Electrical and Computer Engineering, 2017. The University of Cyprus Library holds the printed form of the thesis. Παρά τις σημαντικές εξελίξεις στην τεχνολογία, τα σύγχρονα συστήματα ηλεκτρικής ενέργειας εξακολουθούν να αντιμετωπίζουν κλιμακωτές βλάβες που οδηγούν σε μεγάλης έκτασης συσκοτίσεις. Η ηθελημένη ελεγχόμενη νησιδοποίηση, ή αλλιώς διάσπαση συστήματος ή ελεγχόμενος διαχωρισμός συστήματος, έχει προταθεί ως ένα αποτελεσματικό διορθωτικό μέτρο ελέγχου για τον περιορισμό αυτών των καταστροφικών γεγονότων. Η ελεγχόμενη νησιδοποίηση αποσκοπεί στο να χρησιμοποιηθεί ως μια έσχατη λύση για να προσπαθήσει να σώσει το σύστημα από μια μερική ή πλήρη συσκότιση. Όταν το σύστημα υποστεί μια σοβαρή διαταραχή και τα συμβατικά συστήματα ελέγχου δεν είναι σε θέση να το διατηρήσουν σε ευστάθεια, η ελεγχόμενη νησιδοποίηση μπορεί να καθορίσει σε πραγματικό χρόνο (μέσα σε λίγα δευτερόλεπτα στην πράξη) ένα σύνολο γραμμών που θα αποσυνδεθούν από το σύστημα μεταφοράς ώστε να δημιουργηθούν βιώσιμα και ευσταθή υποσυστήματα, γνωστά και ως νησίδες. Κατά την υιοθέτηση της ηθελημένης ελεγχόμενης νησιδοποίησης, πρέπει να εξεταστούν τρεις βασικές πτυχές: “σε ποια σημεία να διαχωριστεί το σύστημα”, “πότε να διαχωριστεί το σύστημα” και ”τι πρέπει να γίνει μετά τον διαχωρισμό του συστήματος”. Σε αυτή τη διατριβή, προτείνονται αρκετές μέθοδοι ελεγχόμενης νησιδοποίησης για την επίλυση της πρώτης πτυχής. Οι προτεινόμενες μέθοδοι αποσκοπούν στη διάσπαση του συστήματος με ελάχιστη διαταραχή της ροής ισχύος ή ελάχιστη ανισορροπία της ισχύος στις νησίδες, για οποιοδήποτε δεδομένο αριθμό νησίδων, διατηρώντας παράλληλα τις συνοχές των γεννητριών και άλλους στατικούς και δυναμικούς περιορισμούς (π.χ. διαθεσιμότητα μιας γραμμής μεταφοράς, συνδεσιμότητα). Δεδομένου ότι η ευστάθεια των νησίδων που δημιουργούνται εξαρτάται κυρίως από τη συνοχή των γεννητριών εντός των νησίδων, προτείνεται επίσης μια εφαρμογή δύο σταδίων για τον καθορισμό συνεκτικών γεννητριών σε διαταραγμένα συστήματα ηλεκτρικής ενέργειας. Η εφαρμογή αυτή βασίζεται στην ομοιότητα μεταξύ των διασυνδετικών ταλαντώσεων και των καμπυλών ταλάντωσης των γεννητριών. Το ερώτημα για το πότε πρέπει να διαχωριστεί το σύστημα είναι κρίσιμο για την επιτυχία της μεθόδου ελεγχόμενης νησιδοποίησης, δεδομένου ότι πρέπει να αντιμετωπιστούν τα πιθανά προβλήματα λανθασμένου συναγερμού και λανθασμένης χρονικής εκτέλεσης. Μια ενοποιημένη μεθοδολογία που βασίζεται σε ένα area-based Center of Inertia (COI)-referred rotor angle δείκτη εισάγεται για να προσδιορίσει τον καταλληλότερο χρόνο διαχωρισμού του συστήματος. Αυτός ο έγκαιρος καθορισμός του χρόνου για ελεγχόμενη νησιδοποίηση μπορεί να συνδυαστεί με εφαρμογές που καθορίζουν τα σημεία διαχωρισμού του συστήματος. Επιπλέον, σε αυτή τη διατριβή, εξετάζεται η έννοια μιας στρατηγικής για ελεγχόμενη νησιδοποίηση συνδυασμένη με μια εφαρμογή για παράλληλη αποκατάσταση του συστήματος ηλεκτρικής ενέργειας. Για το λόγο αυτό, ένας αλγόριθμος ελεγχόμενης νησιδοποίησης εξελίσσεται λαμβάνοντας υπόψιν περιορισμούς αποκατάστασης του συστήματος ηλεκτρικής ενέργειας (π.χ. πλήρης παρατηρησιμότητα, επαρκής ικανότητα “blackstart” και επαρκής ικανότητα παραγωγής για να καλύπτει την ζήτηση φορτίου σε κάθε νησίδα). Αυτοί οι νέοι περιορισμοί μπορούν να θεωρηθούν ως ένα στάδιο προγραμματισμού της αποκατάστασης του συστήματος ηλεκτρικής ενέργειας. Στη συνέχεια, προτείνεται μια καινοτόμα μέθοδος για να παρέχει λύσεις σε πραγματικό χρόνο τόσο για ελεγχόμενη νησιδοποίηση όσο και για αποκατάσταση του συστήματος ηλεκτρικής ενέργειας βασιζόμενη σε εκτιμημένες καταστάσεις του συστήματος. Η συγκεκριμένη μέθοδος, που αποτελείται από τον προαναφερθέντα αλγόριθμο ελεγχόμενης νησιδοποίησης που εξελίχθηκε, έναν εκτιμητή κατάστασης πραγματικού χρόνου και μια διαδικασία αποκατάστασης του συστήματος ηλεκτρικής ενέργειας, δίνει στο χειριστή του συστήματος την ευελιξία να παρακολουθεί τις νησίδες μετά τη νησιδοποίηση και να τις επανασυνδέει σε σχεδόν πραγματικό χρόνο, μόλις ικανοποιηθούν οι συνθήκες συγχρονισμού τους. Επιπλέον, προτείνεται ένα ενοποιημένο πλαίσιο που αποτελείται από μια καινοτόμα μέθοδο ελεγχόμενης νησιδοποίησης και μια μεθοδολογία εκτίμησης κινδύνου για να αξιολογήσει τον κίνδυνο των μεθόδων ελεγχόμενης νησιδοποίησης στο σύστημα ηλεκτρικής ενέργειας. Το ενοποιημένο πλαίσιο παρέχει στατιστικά στοιχεία σχετικά με τα οφέλη και τους κινδύνους της εφαρμογής μιας ελεγχόμενης νησιδοποίησης, λαμβάνοντας υπόψη τις αβεβαιότητες και τις ανησυχίες που σχετίζονται με την αξιοπιστία της. Για την ολοκλήρωση αυτής της έρευνας, αναπτύχθηκαν δυναμικά δοκιμαστικά συστήματα κατάλληλα για μελέτες μεταβατικής ανάλυσης τα οποία παρέχονται σε ανοικτή πρόσβαση. Despite major advances in technology, modern power systems still experience cascading outages leading to large-scale blackouts. Intentional controlled islanding (ICI), also called system splitting or controlled system separation, has been proposed as an effective corrective control action to mitigate these catastrophic events. ICI is aimed to be used as a final resort to attempt to save the system from a partial or a complete blackout. When the system is subject to a severe disturbance and the conventional control systems are unable to keep the system stable, ICI can determine in real-time (within a few seconds in practice) a set of lines to be disconnected across the transmission system to create sustainable and stable subsystems, also known as islands. When adopting ICI, three key aspects must be addressed: “where to island”, “when to island” and “what to do after islanding”. In this thesis, several ICI schemes are proposed for addressing the first one. The proposed schemes aim to split the system with minimal power-flow disruption or minimal power imbalance within islands, for any given number of islands, while maintaining generator coherencies and other static and dynamic constraints (e.g., transmission line availability, connectivity). Since the stability of islands created is mainly dependent on the coherency of the generators inside the islands, a two-step approach for defining coherent generators in disturbed power systems based on the similarity among their inter-area oscillations and swing curves is also proposed. The question of when to island is critical for the success of the ICI scheme, since the possible issues of false alarm and false dismissal have to be handled. A unified methodology based on area-based Center of Inertia (COI)-referred rotor angle index is introduced to determine the most suitable time for splitting the system. This timely definition of the time for islanding can be combined with approaches to determine the points where to island the system. Furthermore, in this thesis, the concept of a controlled islanding strategy combined with an approach of Parallel Power System Restoration (PPSR) is considered. A proposed ICI algorithm is extended to consider power system restoration constraints (e.g., complete observability, sufficient blackstart (BS) capability and sufficient generation capacity to match the load consumption within each island). These new constraints can be viewed as a power system restoration planning stage. Next, a novel scheme is proposed to provide real-time solutions for both ICI and power system restoration based on estimated states. The particular scheme, which consists of the aforementioned extended ICI algorithm, a real-time state estimator and a power system restoration process, gives the system operator the flexibility to monitor the islands during the post-islanding stage and reconnect them in quasi real time, as soon as their synchronizing conditions are met. In addition, a unified framework that consists of a novel ICI scheme and a risk assessment methodology is proposed to assess the risk of ICI schemes on the electricity system. The unified framework provides insights on the benefits and risks of implementing ICI, considering the uncertainties and concerns related to its reliability. For the completion of this research, dynamic test bed systems suitable for transient analysis studies are developed and provided in open access.

Fault recorders can track the transients in the power system during a fault. However, they cannot provide a wide area picture of the power system operating condition. The provision to track the transients is of great interest for the power system operators. In this paper, a two-stage state estimator (SE), based on both conventional and phasor measurement unit (PMU) measurements, is presented. The estimator is able to track the dynamics of the power system states during a fault. The advantage of the proposed SE is that it does not require full power system observability by the PMU measurements. The two-stage SE was successfully tested on the IEEE 14 and 118 bus systems.

The accurate representation of the transmission line parameters is essential for several monitoring and control applications accommodated in the control center of the power system. In this sense, it is always important to update the database of the transmission line parameters which might be obsolete and/or contain erroneous parameters. The validation and the correction of any inconsistencies related to the power system model is one of the natural applications of the Synchronized Measurement Technology. One way for line parameter refinement is the use of Phasor Measurement Units at the two ends of the transmission line. In this paper, the error that is associated with the calculation of the line parameters is examined. The effect of uncertainties that are introduced to the PMU measurements by both instrument transformers and PMUs on the calculation of the transmission line parameters is investigated by performing several case studies in the IEEE-14 bus system., "© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works." M. Asprou, E. Kyriakides, and M. Albu, "The effect of PMU measurement chain quality on line parameter calculation," 2017 IEEE International Instrumentation and Measurement Technology Conference (I2MTC), Turin, May 2017, pp. 1-6.

Power losses in transmission systems are most of the time seen as a small amount (2-5%) from the total power carried over the network. However, transmission loss allocation may play a crucial role in the congestion management of balancing markets. Several loss allocation and loss cost allocation methods have been proposed and implemented in different markets. Most of these methods are intended to be used post-market. This study presents a novel near-real-time loss allocation method suitable to be applied in real-time markets as envisioned in the smart grid context. The proposed method allocates the total system losses fairly to all the demand and generator buses, by taking into account the dynamical changes of the power network states, which are provided by an accurate state estimation. The power flows required to determine the allocated losses are executed after an economic dispatch procedure that ignores losses, making the choice of the slack bus an independent factor. The proposed method can be used as an accurate real-time pricing for network usage while the resolving of transmission congestion can be more reliable.

The accurate knowledge of the transmission line parameters can be beneficial for several monitoring and control applications accommodated in the power system control center. Actually transmission line parameters are stored in the control center databases (assuming that they are time invariant); however, the databases might be obsolete and contain erroneous parameters. This paper proposes a methodology for identifying and estimating the erroneous transmission line parameters using measurements provided by phasor measurement units (PMUs) and estimated states provided by a state estimator. The main advantage of the proposed methodology is that for the identification of the erroneous transmission lines and the estimation of the line parameters only one PMU is required for the monitoring of the transmission line (i.e., capture measurements related to the transmission line). The proposed methodology is tested in the IEEE 14- and 118-bus systems.

Load shedding constitutes the very last resort for preventing total blackouts and cascading events. Conventional load shedding schemes, which are massively applied in industrial practice, adopt a step-wise approach that usually causes overshedding or fails to prevent frequency decay above the allowable limits. Recently proposed schemes based on real time intelligent control and neural networks achieve the control objective, but fail to minimize the amount of load to be shed due to the delay incurred in consecutive control decisions. This letter proposes a new load shedding scheme, decoupled from the conventional scheme. This scheme, based on the equivalent swing equation of the system, determines the minimal amount of load that should be shed immediately (in a single step) after the load event/disturbance occurs, in order to guarantee system stability.

The capacitive network representation of voids in electric power cables has long been used for the study of the transients generated by a breakdown in an enclosed void. As an alternative to the capacitive representation of the void, the induced charge concept has been introduced by Pedersen and his colleagues. This work examines the induced charge concept from an electrostatic point of view and from measured transients in relation to the change in the capacitance of the system by opposing Pedersen's views.

The state estimator constitutes the cornerstone of the supervisory control and data acquisition system since it provides the power system operating situation in consecutive time intervals. Furthermore, the output of the state estimator is used by other tools responsible for the monitoring and control of the power system. Therefore, there is a need for the power system state estimator to be as accurate and reliable as possible. The main source of uncertainty that may deteriorate the accuracy of a weighted least squares (WLS) state estimator, provided that the network parameters are perfectly known, is the uncertainty that is encompassed in the measurements. It is well known that the measurement chain is not ideal and this information is passed to the state estimator through the measurement weights. In this paper, the effect of the measurement weights, which are calculated by considering both the standard uncertainties associated with the measurement devices and the instrument transformers, on the WLS state estimator is examined.

Improving the efficiency of thermoelectric devices is critical to their widespread adoption. Here a design methodology, formulated on computational and analytical modeling, derives the optimum efficiency and geometry of segmented Bi2Te3–PbTe Thermoelectric Generators (TEGs) between ≈298 K and ≈623 K (ΔT ≈ 325 K). Comparisons between the different TEG designs, in terms of the electrical load to TEG electrical resistance ratio (m = RL/RTEG), are simplified thanks to the devised maximum efficiency to temperature gradient (βmax = η/ΔT) metric. Quasi-computational results of βmax show that the collective Seebeck coefficient Bi2Te3–PbTe ( α ˜ ) design sustains a higher electrical load in relation to the homogeneous Bi2Te3 and PbTe materials. The average ( α ¯ ) and collective ( α ˜ ) Seebeck coefficient Bi2Te3–PbTe configurations, in comparison to Bi2Te3 and PbTe, exhibit a considerably higher (60–68%) source and sink thermal resistance matching (ΘTEG = ΘHx). The proposed segmented Bi2Te3–PbTe ( α ˜ ) TEG yields a peak efficiency of 5.29% for a ΔT of 324.6 K.

The delay of Phasor Measurement Unit (PMU) measurements due to the communication network may affect the performance of real time applications accommodated in a Wide Area Monitoring and Control system. In order to mitigate the effect of the PMU measurement delays, a data delay compensation technique based on a linear predictor is proposed in this paper. The proposed method incorporates autocorrelation Linear Predictive Coding (LPC) to predict the future values of the measured signals and a data delay compensator to compensate the data delays actively. The proposed data delay compensation technique is applied to the IEEE 9-bus test system where it is indicated that the proposed method can compensate the data delays in wide area signals effectively.

Includes bibliographical references (p. 221-234). Number of sources in the bibliography: 139 Thesis (Ph. D.) -- University of Cyprus, Faculty of Engineering, Department of Electrical and Computer Engineering, 2016. The University of Cyprus Library holds the printed form of the thesis. Η αύξηση στην τιμή καθώς και το περιβαλλοντικό αντίκτυπο των ορυκτών καυσίμων έχουν εγείρει το ενδιαφέρον για τις Ανανεώσιμες Πηγές Ενέργειας (ΑΠΕ), ειδικά όσο αφορά τις ανεμογεννήτριες και τα φωτοβολταϊκά συστήματα. Η τεχνολογία κλειδί για να επιτρέψει την ιδιαίτερα υψηλή διείσδυση ΑΠΕ είναι ο αντιστροφέας (μετατροπέας ισχύος βασισμένος σε ηλεκτρονικά ισχύος), που είναι υπεύθυνος για την ορθή διασύνδεση των ΑΠΕ με το δίκτυο ηλεκτροδότησης. Επομένως, η βελτίωση της λειτουργίας του αντιστροφέα ισχύος αποτελεί απαραίτητη προϋπόθεση ώστε οι ΑΠΕ να επιτύχουν: την ορθή λειτουργία υπό οποιεσδήποτε συνθήκες λειτουργίας του δικτύου, να εναρμονιστούν με τις πρόσφατους κανονισμούς δικτύου σχετικά με την διασύνδεση ΑΠΕ, και να προσφέρουν την απαραίτητη στήριξη στο δίκτυο όποτε χρειάζεται. Η συγκεκριμένη διδακτορική διατριβή έχει ως κύριο στόχο την ενίσχυση αντιστροφέα ισχύος όσο αναφορά την λειτουργία κατά την διάρκεια βραχυκυκλωμάτων καθώς και την ποιότητα της εγχεόμενης ισχύος. Η ενίσχυση του αντιστροφέα δύναται να επιτευχθεί βελτιώνοντας τα κύρια υποσυστήματα της μονάδας ελέγχου του. Ο ελεγκτής του αντιστροφέα βασίζεται στη μέθοδο συγχρονισμού, στον ελεγκτή ρεύματος και στον ελεγκτή ισχύος. Η απόκριση της μονάδας συγχρονισμού επηρεάζει άμεσα την λειτουργία των λοιπών υποσυστημάτων του ελεγκτή καθώς και την λειτουργία του αντιστροφέα και κατ’ επέκταση την λειτουργία του συστήματος ΑΠΕ. Επομένως, η διατριβή εστιάζει ιδιαιτέρως στην βελτίωση της μεθόδου συγχρονισμού και προτείνει νέες μεθοδολογίες συγχρονισμού (για μονοφασικούς και τριφασικούς αντιστροφείς). Οι προτεινόμενες μεθοδολογίες συγχρονισμού επιτυγχάνουν την ταχύτατη και υψηλής ακριβείας απόκριση υπό οποιεσδήποτε συνθήκες του δικτύου στο σημείο διασύνδεσης. Επιπλέον, ένα νέος ελεγκτής ρεύματος έχει υλοποιηθεί για την ορθή ρύθμιση των εγχεόμενων ρευμάτων του αντιστροφέα όταν η τάση στο σημείο διασύνδεσης είναι αρμονικά παραμορφωμένη ή παρουσιάζει βυθίσεις λόγω σφαλμάτων. Επίσης, προηγμένες μεθοδολογίες έχουν προταθεί για τον ελεγκτή ισχύος ώστε να επιτυγχάνεται η ορθή λειτουργία του αντιστροφέα κατά την διάρκεια βραχυκυκλωμάτων. Τα πειραματικά αποτελέσματα επιβεβαιώνουν ότι οι προτεινόμενες μεθοδολογίες για τον συγχρονισμό και έλεγχο του αντιστροφέα μπορούν να βελτιώσουν σημαντικά την λειτουργία του αντιστροφέα και επομένως και του συστήματος ΑΠΕ, όσο αναφορά την ποιότητα της εγχεόμενης ισχύος καθώς και την ορθή και δυναμική απόκριση του συστήματος κατά την διάρκεια βραχυκυκλωμάτων στο δίκτυο. Σύμφωνα με μελέτες που έχουν γίνει στα πλαίσια της διατριβής, καταδεικνύεται ότι η βελτίωση της λειτουργίας του αντιστροφέα από τις προτεινόμενες μεθοδολογίες επιφέρει ευεργετικά αποτελέσματα στην αυξημένη διείσδυση των ΑΠΕ λόγω της προηγμένης τους λειτουργιά και στην ενίσχυση της ευστάθειας και την ποιότητα ισχύος ολόκληρου του συστήματος ηλεκτροδότησης. Επιπλέον, στην διατριβή αυτή περιλαμβάνεται μελέτη για διαφορετικές στρατηγικές ελέγχου των ΑΠΕ κατά την διάρκεια βραχυκυκλωμάτων στο δίκτυο. Η μελέτη καταδεικνύει κάποια προβλήματα που μπορούν να προκληθούν στην λειτουργία των ΑΠΕ κατά το βραχυκύκλωμα τα οποία μπορούν να απειλήσουν την ευστάθεια του συστήματος ηλεκτροδότησης και προτείνονται τρόποι αντιμετώπισης. Σε γενικές γραμμές, η διατριβή προτείνει διάφορες τεχνικές οι οποίες μπορούν να βελτιώσουν την λειτουργία του αντιστροφέα και την διασύνδεση των ΑΠΕ. Οι προτεινόμενες μεθοδολογίες επιδρούν ευεργετικά στη βελτίωση της λειτουργία ενός συστήματος ΑΠΕ, στην ενίσχυση της ευστάθειας και της ποιότητας ισχύος του συστήματος ηλεκτροδότησης, και στη δημιουργία εχεγγύων για την αύξηση της διείσδυσης των ΑΠΕ, το οποίο είναι ιδιαίτερα επωφελές για το περιβάλλον. The increasing price and the environmental impact of fossil fuels have grown the attention to modern Renewable Energy Sources (RES), such as wind and solar systems. The key technology for enabling a high penetration of RES is the power electronic based Grid Side Converter (GSC), which is responsible for the proper injection of the produced energy into the power grid. Thus, there is a need to advance the operation of the GSC to ensure that RES will be able to meet the modern grid regulations, to operate properly under any grid conditions, and to ensure the support to the grid when needed. The main objective of this Ph.D. dissertation is to enhance the performance of the GSC with regards to its Fault Ride Through (FRT) operation and to its power quality, through the improvement of the main units of the GSC controller. The design of the GSC controller is based on a fast and robust synchronization method, an advanced current controller, and a power controller enhanced with FRT capabilities. The most crucial aspect of the control of a grid-connected RES is the synchronization method. Thus, this Ph.D. dissertation proposes several single- and three-phase synchronization methods that can achieve a fast and accurate response under any grid conditions. Further, a current control that enables a proper operation under grid faults is proposed and some advanced methodologies for enabling the FRT operation of GSC are suggested. The proposed methodologies are directly applied to the GSC controller and it has been experimentally proved that the proposed methods for the synchronization and control of the GSC can improve the performance of RES, in terms of dynamic and FRT operation, as well as enhancing the quality of the injected currents. Investigations performed depict significant impacts from advancing the performance of the GSC. For example, the improved operation of the GSC enables a higher penetration of RES and enhances the power quality and stability of the power system under an increased penetration of RES. In addition to the above contributions, a benchmarking study of different fault ride through strategies for RES has been performed on a dynamic test power system, where some issues have been highlighted and modifications are proposed for the current grid regulations in order to improve the system stability. Further, a centralized control methodology for RES has been suggested to enhance the voltage stability of the power system by utilizing the improved capabilities of RES.

The ability of monitoring a laboratory scale power system is crucial for research and educational purposes. This paper proposes the development of a low-cost real-time platform for monitoring a laboratory scale power system. The design and development of this novel monitoring system is based on a TMS320F28335 microcontroller of Texas Instruments. The microcontroller reads voltage and current measurements from several locations of the laboratory scale power system, processes these measurements and then sends the results to a personal computer. The user can monitor in real-time the operation of the power system through the implemented graphical user interface. The developed system can achieve an accurate and real-time monitoring of a laboratory scale power system which is particularly useful in the educational process for understanding the main power engineering practices. Moreover, novel algorithms regarding the stability, the state estimation, the operation and the monitoring of power systems can be experimentally validated by utilizing the proposed monitoring system. The demonstration of the proper operation of the prototype monitoring system is available online as a video.

A Renewable Energy Source (RES), enhanced with Fault Ride Through (FRT) capability, can provide proper voltage and frequency support to the power grid under several disturbances. This paper investigates how a realistic dynamic power system with high penetration of RES reacts under different operating conditions. More specifically, the power system operation when RES operates according to the current grid regulations of the Cyprus TSO is demonstrated. For the purposes of this investigation, a RES is interconnected with the IEEE 9-bus test system, reinforced with an appropriate directional over-current protection scheme, and dynamic electromagnetic transient simulation results are provided.

Accurate load models are extremely important for the operation planning and power system control. Load characteristics critically influence the power system behavior especially during events that frequently occur in the power system. The introduction of synchronized measurements helps to collect high quality data for more reliable load models. This paper presents an effective method for modeling and identification of dynamic loads. Using synchronized measurements a parameter estimation of a dynamic load model during various events is performed. For more realistic results a well-studied and accepted model, the exponential recovery load model, is used. The effectiveness of the parameter estimation method is examined through simulations applied on the 39-bus New England system.

The controllers of single-phase grid-tied inverters require improvements to enable distribution generation systems to meet the grid codes/standards with respect to power quality and the fault ride through capability. In that case, the response of the selected synchronization technique is crucial for the performance of the entire grid-tied inverter. In this paper, a new synchronization method with good dynamics and high accuracy under a highly distorted voltage is proposed. This method uses a Multi-Harmonic Decoupling Cell (MHDC), which thus can cancel out the oscillations on the synchronization signals due to the harmonic voltage distortion while maintaining the dynamic response of the synchronization. Therefore, the accurate and dynamic response of the proposed MHDC-PLL can be beneficial for the performance of the whole single-phase grid-tied inverter.

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The common feature of many monitoring and control applications that will be accommodated in the future Wide Area Monitoring and Control system will be the quasi real time execution, exploiting the fast reporting rate of the Phasor Measurement Unit (PMU). A critical parameter for the timely execution and the good performance of such real time applications is the delay that the PMU measurements experience during their transfer between successive processing layers — for example, from the substation level to the control center. The associated delays, mainly due to the communication infrastructure, should be quantified and considered in the process of a real time application. Therefore, in this paper the delay associated to real PMU measurements that are transferred through a heterogeneous communication network (3G) is estimated for a specific measurement set-up used in the Romanian distribution system. Further, the respective delay will be considered in a numerical simulated measurement environment which is used by a real time state estimator to investigate its impact on the real time performance.

Sponsors: et al. Frederick University IEEE Cyprus Section IEEE Region 8 Technical University of Cyprus University of Cyprus Conference code: 122340

In this paper, we consider the detection of suspiciously high correlation between malicious Internet users that are collaborating in order to cause a Denial of Service (DoS) Attack. The main goal is to recognise cyber incidents (more specifically, collaboration/dependency between different users) in order to ultimately isolate their behavior and avoid the consequenses of the DoS attack. The method relies on the analysis of the data traffic across the concerned network (with both incoming and outgoing traffic) in an effort to identify correlations between different users. The paper models normal and malicious behaviour via hidden Markov models, and analyses the performance of the method using both mathematical reasoning and simulations. © 2016 IEEE.

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The main task of the state estimator in power systems is the provision of the power system state accurately. In order to achieve this, the measurement set has to be validated by identifying erroneous measurements. This is usually achieved by using either the Chi-square or the Largest Normalized Residual test. In both tests, the estimated states that are provided by the state estimator and the measurement variances included in the measurement error covariance matrix are used for detecting the erroneous measurements. The measurement error covariance matrix is usually formulated using the accuracy of the measurement device only, ignoring the quality of other elements in the measurement chain such as the instrument transformers. In this paper, the effect of instrument transformer measurement quality on the bad data detection algorithm is investigated. Further, simulation results based on the IEEE 118-bus system are provided.

It is shown that zero beam-squinting can be achieved in both series fed antenna arrays and leaky-wave antennas by employing two parallel-connected metamaterial transmission lines with equal positive group delays, but with opposite phase velocities. The theory of operation is presented that enables the design of an off-broadside leaky-wave antenna with zero beam-squinting over a relative bandwidth. Subsequently, the antenna operation is validated using an array factor analysis. © 2016 IEEE.

Monitoring utility-scale solar arrays was shown to minimize cost of maintenance and help optimize the performance of the array under various conditions. In this paper, we describe the design of an 18 kW experimental facility that consists of 104 panels fitted with smart monitoring devices. Each of these devices embeds sensors, wireless transceivers, and relays that enable continuous monitoring, fault detection, and real-time connection topology changes. The facility enables networked data exchanges via the use of wireless data sharing with servers, fusion and control centers, and mobile devices. Research planned at this stage includes developing machine learning methods for fault detection. Preliminary simulation results on fault detection using machine learning are given in this paper.

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Many real-life optimization problems often face an increased rank of nonsmoothness (many local minima) which could prevent a search algorithm from moving toward the global solution. Evolution-based algorithms try to deal with this issue. The algorithm proposed in this paper is called GAAPI and is a hybridization between two optimization techniques: a special class of ant colony optimization for continuous domains entitled API and a genetic algorithm (GA). The algorithm adopts the downhill behavior of API (a key characteristic of optimization algorithms) and the good spreading in the solution space of the GA. A probabilistic approach and an empirical comparison study are presented to prove the convergence of the proposed method in solving different classes of complex global continuous optimization problems. Numerical results are reported and compared to the existing results in the literature to validate the feasibility and the effectiveness of the proposed method. The proposed algorithm is shown to be effective and efficient for most of the test functions.

The estimation of the states of an electric power system, that is, the magnitude and angle of the voltage at all buses, is a very critical input to many monitoring and control functions of power systems. The recently witnessed rapid deployment of synchronized measurement technology (SMT) in power systems, has led to research advancements in the state estimation technology that introduce the notion of hybrid state estimation. These techniques incorporate the synchrophasors provided by the Phasor Measurement Units (PMUs) in the state estimation process, thus improving the state estimation accuracy. However, both the traditional as well as the hybrid techniques, assume a pre-defined configuration and characteristics of the measurement devices. This work explores how semantic modelling and reasoning techniques may contribute to the online configuration of the state estimation architectures given the available measurement capabilities at each moment., IEEE Published version: G. M. Milis, M. Asprou, E. Kyriakides, C. G. Panayiotou and M. M. Polycarpou, "Semantically-Enhanced Configurability in State Estimation Structures of Power Systems," 2015 IEEE Symposium Series on Computational Intelligence, Cape Town, 2015, pp. 679-686. doi: 10.1109/SSCI.2015.104 keywords: {phasor measurement;state estimation;PMU;electric power system;phasor measurement units;power system control;power system monitoring;reasoning techniques;semantic modelling;semantically-enhanced configurability;state estimation architectures;state estimation process;state estimation structures;state estimation technology;synchronized measurement technology;Current measurement;Monitoring;Phasor measurement units;Semantics;State estimation;Transmission line measurements;Voltage measurement}, URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7376678&isnumber=7376572 © 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, in-cluding reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to serv-ers or lists, or reuse of any copyrighted component of this work in other works.

This paper presents a nonlinear parameter estimator for synchronous machines based on the unscented Kalman filter. The proposed methodology uses voltages and current signals recorded from the stator and the field winding to update the parameters of the classical model of the synchronous machine for stability studies. The methodology can be applied without interrupting the normal operation of the generator. Park's Transformation is included in the estimation process to relate the stator measurements (in abc components) to the nonlinear voltage equations in the qd0 reference frame. The proposed robust methodology has been validated using real and simulated data to estimate the model parameters of a 483-MVA round rotor machine.

This paper presents a new hybrid constrained power system state estimator. The conventional and synchrophasor measurements are simultaneously incorporated in the estimation problem without using any transformation of measurements. This constrained formulation makes it possible to take advantage of information from phasor measurement unit (PMU) branch current and voltage measurements, improving the accuracy of the existing estimators. The methodology is applied on the IEEE 14-, 57-, and 118-bus test systems, and its performance is compared with other hybrid estimators.

This paper computes the uncertainties associated with the power system state variables obtained with the help of phasor measurement units (PMUs). An integer-quadratic-programming-based method is used to determine the minimum number and the optimal locations of the PMUs to ensure complete topological observability of the system. Three approaches are used to estimate the uncertainties in the state variables: the use of the classical uncertainty propagation theory, the Monte Carlo method, and the random fuzzy variables (RFVs). The methods are applied on a test system, and the results are presented. The choice of method depends on the application; suggestions are offered based on the conclusions of the work in this paper.

This paper presents a method for the use of synchronized measurements for complete observability of a power system. The placement of phasor measurement units (PMUs), utilizing time-synchronized measurements of voltage and current phasors, is studied in this paper. An integer quadratic programming approach is used to minimize the total number of PMUs required, and to maximize the measurement redundancy at the power system buses. Existing conventional measurements can also be accommodated in the proposed PMU placement method. Complete observability of the system is ensured under normal operating conditions as well as under the outage of a single transmission line or a single PMU. Simulation results on the IEEE 14-bus, 30-bus, 57-bus, and 118-bus test systems as well as on a 298-bus test system are presented in this paper.

This article deals with the synchronized measurement technology that has the potential of becoming the backbone for real-time monitoring system. The secure and reliable operation of modern power systems is an increasingly challenging task due to the ever-increasing demand for electricity, the growing number of interconnections, penetration of variable renewable energy sources, and deregulated energy market conditions. Power companies in different parts of the world are therefore feeling the need for a real-time wide area monitoring, protection, and control (WAMPAC) system. Synchronized measurement technology (SMT) has the potential of becoming the backbone of this system. The major advantages of using SMT are that 1) the measurements from widely dispersed locations can be synchronized with respect to a Global Positioning System (GPS) clock, 2) voltage phase angles can be measured directly, which was so far technically infeasible, and 3) the accuracy and speed of energy management system (EMS) applications increases manifold.