Multi-Area Frequency Restoration Reserve Sizing

Frequency Restoration Reserves are traditionally sized using deterministic methods. The constant growth in non-dispatchable renewable energy, however, is increasing the importance of probabilistic methods for reserve sizing. In addition, as the geographical scope of reserve sizing expands, overall power imbalance stochasticity is reduced. In this article, we propose a probabilistic method for shared cross-border frequency restoration reserve commitment and sizing, based on the concept of system generation margin and employing mathematical optimization. The aim is to reduce overall reserve volumes and costs. The cross-border interconnection capacities among countries are taken into account, and the shared uncertainty across interconnections is addressed via a novel robust approach. The method is tested on the cross-border system of south-east Europe that includes 9 countries. 5 different operational scenarios are used and a detailed calculation of the uncertainty distributions in each country is employed. Results show that cross-border shared sizing can significantly reduce overall reserve volumes and costs in a secure way.©2023 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.fi=vertaisarvioitu|en=peerReviewed

Compliance of Distribution System Reactive Flows with Transmission System Requirements

Transmission system operators (TSOs) often set requirements to distribution system operators (DSOs) regarding the exchange of reactive power on the interface between the two parts of the system they operate, typically High Voltage and Medium Voltage. The presence of increasing amounts of Distributed Energy Resources (DERs) at the distribution networks complicates the problem, but provides control opportunities in order to keep the exchange within the prescribed limits. Typical DER control methods, such as constant cosϕ or Q/V functions, cannot adequately address these limits, while power electronics interfaced DERs provide to DSOs reactive power control capabilities for complying more effectively with TSO requirements. This paper proposes an optimisation method to provide power set-points to DERs in order to control the hourly reactive power exchanges with the transmission network. The method is tested via simulations using real data from the distribution substation at the Sundom Smart Grid, in Finland, using the operating guidelines imposed by the Finnish TSO. Results show the advantages of the proposed method compared to traditional methods for reactive power compensation from DERs. The application of more advanced Model Predictive Control techniques is further explored.©2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).Part of this work was carried out in the SolarX research project with financial support provided by Business Finland, 2019–2021 (grant No. 6844/31/2018).fi=vertaisarvioitu|en=peerReviewed

Contribution to the optimal utilization of energy resources and infrastructure for the operation and development of electric energy systems

Modern power systems are experiencing a period of fast-paced transformation in terms of their operation and planning paradigms. This transformation is driven by the increasing presence of new energy resources, mainly renewable energy, and digitalisation, which is a natural evolution that occurs in many industries. Both drivers are caused by necessity and opportunity at the same time. For example, the need for carbon emissions reduction mandates the use of renewable energy and synergies between energy sectors, while ICT offers the opportunity for more efficient management of resources and better services. The result is a number of new challenges that utilities and power system engineers have to address such as yielding local flexibility potential, electrification of heating and transportation, renewable energy integration, TSO-DSO coordination and cross-border cooperation. The topic of this PhD thesis is the optimal utilisation of energy resources for the operation and development of distribution networks and the operational cooperation of interconnected electric energy systems. It focuses on the following research questions: a) How Day-ahead (DA) scheduling of Distributed Energy Resources (DERs) can take place in a distributed manner without the exchange of private information between actors, b) how Distribution Use-of-System (DUoS) tariffs can be redesigned in order to motivate DER flexibility while ensuring cost recovery and retaining simplicity for the end-users, and c) How Transmission System Operators (TSOs) can cooperate for the sizing (also called dimensioning) of Frequency Restoration Reserves (FRR) across many Balancing Areas (BAs) in order to reduce costs and volumes?On the first question, this thesis proposes a novel method for distributed optimisation of DER in Distribution Networks (DNs), using Distribution Locational Marginal Prices (DLMPs), aiming to alleviate line and voltage problems. The method minimises the exchange of information between the DER aggregators and the Distribution System Operator (DSO), who coordinates the process. The synergy between demand and generation is modelled and demonstrated via simulations. Furthermore, an approach for increasing convergence speed is proposed, using topological information and highlighting the importance of price sensitivity on convergence speed and modelling accuracy. The proposed methodology is validated in two different distribution networks, successfully reaching the optimal solution with a threefold reduction in the number of iterations. On the second question, four chapters are devoted. First, a new model is proposed for designing DUoS tariffs that are more adjusted to short-term conditions and can harvest part of the available flexibility from DER while retaining revenue adequacy for the DSO and some simplicity. Bilevel optimisation is employed for the modelling of the problem, with the DSO at the upper level, designing tariffs to minimise operational costs, and flexible prosumers at the lower level minimising their energy and network usage costs. Contrary to the previous literature, the proposed methodology allows for tariffs to have temporal and spatial granularity, by using a detailed representation of the physical network in the upper level. In order to retain simplicity and intelligibility, the tariffs are allowed to have discrete levels and, more importantly, are constrained to few tariff patterns per planning period, using machine learning techniques. The proposed method is tested using out-of-sample simulations in order to validate the effectiveness of the tariffs and the clustering-based reduction of complexity under realistic conditions. The case studies suggest that properly designed tariff patterns can yield a significant percentage of the available cost reduction due to flexibility motivation, as for example, only 4 tariff patterns can yield 78% of the available cost reduction compared to the theoretical optimal. The next chapter expands the case studies on DUoS tariffs by employing State Estimation (SE) techniques. SE is used for obtaining a full state of the distribution network, which is necessary for implementing the tariff design method, in the absence of the necessary field data. A full validation framework is built to test the efficacy of this synergy where the proposed solution (SE and DUoS tariff design) is compared to the theoretical optimal solution (centralised optimisation under perfect knowledge). The results show that the proposed solution achieves over 75% of the optimal efficacy which is measured in operational cost reduction. The proposed solution can be used in the immediate future by system operators due to its reliance on fewer and easily accessible field data. An additional contribution to the second question is an expansion of the tariff design model by considering its synergies with Local Flexibility Markets (LFMs). More specifically, in this model, the DSO in the upper level minimises flexibility procurement costs, instead of curtailment, while in the lower level an aggregator of an EV parking lot, optimises charging costs and and profits from selling flexibility to the DSO, in the form of capacity limitation. The case studies demonstrate that flexibility products such as capacity limitation contracts, are the preferable method for reducing demand during peak hours, while more elaborate demand response incentives are necessary in more complex cases. One of these cases is that of excess PV generation that can be absorbed by neighbouring flexible demand. In such cases, DUoS tariffs have the necessary precision in demand shifting incentivisation, therefore they should be preferred. The last contribution to the second question is a more complete model of DUoS tariffs design that includes investment decisions. The proposed method is a planning tool to be used by system operators under the supervision of the regulatory authorities which assists them in deciding network investment decisions and their cost recovery via DUoS tariffs that are variable and can motivate demand flexibility. The planning horizon is that of investment decision-making, i.e., years, and uncertainty on future demand and generation are considered. Moreover, fairness objectives can also be part of the overall optimization. The case studies show that such a tool is superior in reducing investment costs for DSOs and optimizing social welfare, compared to the business-as-usual method. On the third question, this thesis has contributed with a novel probabilistic method for shared cross-border FRR commitment and sizing, based on the concept of System Generation Margin (SGM) and employing mathematical optimization. The cross-border interconnection capacities among countries are taken into account, and the shared uncertainty across interconnections is addressed via a novel robust approach. The method is tested using the region of southeast Europe and 5 scenarios for generation and demand. Results demonstrate that the method leads to an average of 19% reduction in FRR volume and over 50% reduction in costs, which encourages further investigation of this approach. Overall, this PhD thesis demonstrates the value of using efficient resource management, ICT, and DER flexibility to optimize the operation and planning of power system infrastructure by applying these principles to 3 adjacent research topics.Η διατριβή πραγματεύεται περιοχές της λειτουργίας των Συστημάτων Ηλεκτρικής Ενέργειας (ΣΗΕ) για τις οποίες υπάρχει έντονο ερευνητικό ενδιαφέρον. Τέτοιες περιοχές είναι: α) μηχανισμοί και διαδικασίες έτσι ώστε να αξιοποιούνται βέλτιστα οι υποδομές και οι ενεργειακοί πόροι που βρίσκονται στο επίπεδο του δικτύου διανομής (ΔΔ) ηλεκτρικής ενέργειας, καθώς και β) η διασυνοριακή συνεργασία συστημάτων για την από κοινού διαστασιολόγηση εφεδρειών συχνότητας. Η διατριβή επικεντρώνεται πρώτα στα δίκτυα διανομής και την εύρεση της οριακής τιμής ανά μονάδα ηλεκτρικής ενέργειας με χρήση κατανεμημένων αλγορίθμων που δεν απαιτούν την χρήση ιδιωτικών πληροφοριών για τους χρήστες του δικτύου (καταναλώσεων, παραγωγών). Στα πλαίσια της διατριβής προτείνεται κατάλληλο γραμμικό ισοδύναμο μοντέλο για την κατά προσέγγιση εύρεση της οριακής τιμής με αποδεκτό σφάλμα. Επιπλέον, προτείνεται μέθοδος επιτάχυνσης της σύγκλισης προς την βέλτιστη λύση του προβλήματος με χρήση πληροφοριών της τοπολογίας του δικτύου. Η προτεινόμενη μέθοδος επιτυγχάνει τουλάχιστον τριπλάσια ταχύτητα σύγκλισης σε σχέση με άλλες μεθόδους στην υπάρχουσα βιβλιογραφία και σφάλματα από το γραμμικό ισοδύναμο μοντέλο μικρότερα του 1%. Η χρήση της οριακής τιμής ως σήμα κινητοποίησης ευελιξίας από Διεσπαρμένες Πηγές Ενέργειας (ΔΠΕ) στα ΔΔ χρειάζεται σημαντικές υποδομές μέτρησης και αυτοματοποίησης. Για το λόγο αυτό, η πρόσφατη βιβλιογραφία, στρέφεται σε εναλλακτικούς τρόπους ενεργοποίησης των ΔΠΕ. Το κύριο μέσο που εξετάστηκε είναι οι κυμαινόμενες Χρεώσεις Χρήσης Δικτύου (ΧΧΔ). Η διατριβή αυτή προτείνει ένα ολοκληρωμένο πλαίσιο σχεδιασμού τέτοιων χρεώσεων, που συνδυάζει την ανάκτηση εσόδου στο οποίο αποσκοπούν οι ΧΧΔ με την χρονική μετατόπιση της ζήτησης για την εξυπηρέτηση των αναγκών του συστήματος. Στο πρώτο μέρος της ανάπτυξης του σχετικού πλαισίου, μελετήθηκε ο σχεδιασμός κυμαινόμενων ΧΧΔ με χρήση μεθόδων που μοντελοποιούν ταυτόχρονα και την απόκριση της ζήτησης, προσθέτοντας έτσι ένα επιπλέον επίπεδο ακρίβειας στις αποφάσεις του μοντέλου. Χρησιμοποιήθηκαν κατάλληλα μαθηματικά εργαλεία που βασίζονται στην θεωρία παιγνίων και τον μαθηματικό προγραμματισμό. Συγκεκριμένα, το πρόβλημα περιγράφεται ως ένα παίγνιο τύπου Stackelberg, ή ηγέτη-ακολούθου, όπου ο ηγέτης (διαχειριστής) καθορίζει τις ΧΧΔ και οι ακόλουθοι (ΔΠΕ) αντιδρούν ορθολογικά στις χρεώσεις αυτές. Ο βαθμός λεπτομέρειας των ΧΧΔ είναι επιλογή του χρήστη της μεθόδου και μπορεί να φτάσει την ανά ζυγό του δικτύου και περίοδο λειτουργίας διακύμανση. Κύριο χαρακτηριστικό της μεθόδου είναι η χρήση μηχανικής μάθησης για την μείωση της πολυπλοκότητας των ΧΧΔ που σχεδιάζονται καθώς η καθημερινή διακύμανση ζήτησης και παραγωγής ανάγεται σε λίγα αντιπροσωπευτικά ημερήσια μοτίβα που καλούνται αντιπροσωπευτικές ημέρες. Τα αποτελέσματα έδειξαν ότι οι κυμαινόμενες ΧΧΔ είναι εξαιρετικά αποτελεσματικές στη μετατόπιση της ζήτησης ακόμη και με χρήση λίγων αντιπροσωπευτικών ημερών.Στα πλαίσια της ευρύτερης εφαρμογής μελετήθηκε η περίπτωση όπου τα δεδομένα πεδίου (ηλεκτρικά μεγέθη όπως ισχύς, τάση, ρεύμα, κλπ.) που χρειάζεται η μέθοδος δεν προέρχονται από πραγματικές μετρήσεις αλλά από εκτιμητή κατάστασης που βασίζεται σε λιγότερες και περισσότερο ετερογενείς μετρήσεις, προσομοιώνοντας έτσι την πραγματικότητα που αντιμετωπίζουν οι περισσότεροι διαχειριστές σήμερα. Σε επόμενα στάδια της διατριβής επεκτάθηκε το μοντέλο σχεδίασης ΧΧΔ με σκοπό να ενσωματώνει την δυνατότητα του διαχειριστή να αγοράζει επιπλέον υπηρεσίες ευελιξίας από ΔΠΕ. Οι υπηρεσίες αυτές έχουν την μορφή συμβολαίων δυναμικού περιορισμού μέγιστης διαθέσιμης ισχύος και είναι αρκετά χρήσιμες για ΔΠΕ που έχουν υψηλές αιχμές, όπως φορτιστές ηλεκτρικών οχημάτων. Από τις σχετικές προσομοιώσεις, έγινε εμφανές ότι οι δύο μέθοδοι κινητοποίησης ευελιξίας (ΧΧΔ και υπηρεσίες περιορισμού μέγιστης ισχύος) αναπτύσσουν ενδιαφέρουσες και χρήσιμες συνέργειες. Στο τελευταίο μέρος της έρευνας γύρω από τις ΧΧΔ, η μέθοδος συμπεριέλαβε τις αποφάσεις επενδύσεων για επέκταση της χωρητικότητας του ΔΔ καθώς και το αντίστοιχο κόστος. Τέλος, η παρούσα διατριβή μελέτησε την διασυνοριακή συνεργασία συστημάτων με σκοπό την μείωση της ισχύος και του κόστους της εφεδρείας αποκατάστασης συχνότητας (ΕΑΣ) (ή δευτερογενούς εφεδρείας). Αναπτύχθηκε μέθοδος για την από κοινού διαστασιολόγηση της εφεδρείας σε πολλαπλά γειτονικά συστήματα η οποία συμπεριλαμβάνει την σχετική αβεβαιότητα γύρω από τις ανάγκες τέτοιας εφεδρείας και το πως η διασυνοριακή σύνδεση την επηρεάζει. Έγινε δοκιμή της μεθόδου, σε μορφή προσομοίωσης, με χρήση πραγματικών δεδομένων από 9 χώρες της νοτιοανατολικής Ευρώπης

Applications of Clustering on Distribution Use-of-System Τariff Design

Εθνικό Μετσόβιο Πολυτεχνείο--Μεταπτυχιακή Εργασία. Διεπιστημονικό-Διατμηματικό Πρόγραμμα Μεταπτυχιακών Σπουδών (Δ.Π.Μ.Σ.) "Επιστήμη Δεδομένων και Μηχανική Μάθηση

An analytical method for optimal allocation of distributed generation in radial distribution networks.

166 σ.Σκοπός της διπλωματικής εργασίας είναι η επίλυση του προβλήματος της βέλτιστης τοποθέτησης μονάδων διεσπαρμένης παραγωγής (ΜΔΠ) με αναλυτική προσέγγιση με σκοπό: (α) την ελαχιστοποίηση των απωλειών ενεργού ισχύος και (β) τη μεγιστοποίηση του οικονομικού κινήτρου του διαχειριστή του δικτύου σε ακτινικά δίκτυα διανομής. Με την τοποθέτηση ΜΔΠ, δεν μειώνονται μόνο οι απώλειες, αλλά επίσης βελτιώνονται οι τάσεις στους ζυγούς του συστήματος. Στην παρούσα εργασία, υλοποιήθηκε αλγόριθμος σε περιβάλλον MATLAB για τον υπολογισμό του βέλτιστου πλήθους, των θέσεων και της ονομαστικής ισχύος των ΜΔΠ. Για την καλύτερη και πιο εύχρηστη εφαρμογή του προγράμματος από το χρήστη δημιουργήθηκε και γραφικό περιβάλλον (GUI). Αρχικά γίνεται ανάλυση ροών φορτίου με τη μέθοδο Newton-Raphson και έπειτα υπολογίζονται οι απώλειες του υπό μελέτη δικτύου. Στη συνέχεια, μέσω των μεθόδων βέλτιστης τοποθέτησης ΜΔΠ υπολογίζονται: το βέλτιστο πλήθος, οι θέσεις (ζυγοί) και η ονομαστική ισχύς των ΜΔΠ. Τέλος, υπολογίζονται οι απώλειες ενεργού ισχύος του δικτύου και το χρηματικό κίνητρο μετά την τοποθέτηση των ΜΔΠ, με τη βοήθεια της ανάλυσης ροών φορτίου. Οι αλγόριθμοι που υλοποιήθηκαν εφαρμόστηκαν σε τέσσερα δίκτυα 4, 10, 33 και 69 ζυγών. Τα αποτελέσματα των μεθόδων της εργασίας παρουσιάζονται, συγκρίνονται και εξάγονται ειδικά και γενικά συμπεράσματα.The current Diploma Thesis deals with the optimal allocation of Distributed Generators (DGs) in radial distribution networks using an analytical approach in order: (a) to maximize the power loss reduction, (b) to maximize the financial incentive. The optimal DG allocation offers, not only active power losses reduction but also an improvement to the voltage profile of the network. In the present diploma thesis, an algorithm was developed in MATLAB environment for calculating the optimal number, location and size of DGs. A graphic user interface (GUI) was created to make the program user-friendly. Initially, a load flow analysis, with Newton-Raphson method, is calculated, and then line losses of the studied network are calculated. After that, using an analytical optimal DG allocation method, the optimal number, location and size of DGs are calculated. Finally, line losses are calculated along with the financial incentive using load flow analysis. The algorithms developed for the current Thesis were tested on four networks with 4, 10, 33 and 69 buses, respectively. The application results are presented compared and application specific conclusions are drawn.Παναγιώτης Γ. Πεδιαδίτη

Synergies between Distribution Use-of-System Tariffs and Local Flexibility Markets

Managing flexibility is an important element of future distribution networks with more than one mechanisms aiming at this goal. Recently proposed methods include variable distribution use-of-system tariffs and flexibility markets. This paper proposes a model for designing variable tariffs under the presence of flexibility products, such as capacity limits offered by aggregators, and studies their synergies. A detailed model of the network power flows is considered and tariffs can have temporal granularity, while retaining simplicity and cost recovery for the system operator. The flexibility products' cost functions are calculated in detail. Case studies illustrate that flexibility products are preferable as a means of motivating flexibility as long as their are priced close to their actual value. As their pricing increases beyond that, tariffs become increasingly preferable

A Review of the Energy Storage Systems of Non-Interconnected European Islands

The ongoing energy transition has caused a paradigm shift in the architecture of power systems, increasing their sustainability with the installation of renewable energy sources (RES). In most cases, the efficient utilization of renewable energy requires the employment of energy storage systems (ESSs), such as batteries and hydro-pumped storage systems. The need for ESS becomes more apparent when it comes to non-interconnected power systems, where the incorporation of stochastic renewables, such as photovoltaics (PV) systems, may more frequently reduce certain power quality indicators or lead to curtailments. The purpose of this review paper is to present the predominant core technologies related to ESSs, along with their technical and life cycle analysis and the range of ancillary services that they can provide to non-interconnected power systems. Also, it aims to provide a detailed description of existing installations, or combinations of installations, in non-interconnected European islands. Therefore, it provides an overview and maps the current status of storage solutions that enhance the sustainable environmentally friendly operation of autonomous systems

KP-LAB Knowledge Practices Laboratory -- Specifications and Prototype of the Knowledge Repository (V.3.0) and the Knowledge Mediator (V.3.0)

deliverablesThis deliverable reports the technical and research development performed until M36 (January 2009) within tasks T5.2 and T5.4 of WP5 in the KP-Lab project, per the latest Description of Work (DoW) 3.2 [DoW3.2]. The described components are included in the KP-Lab Semantic Web Knowledge Middleware (SWKM) Prototype Release 3.0 software that takes place in M36. This release builds on the Prototype Release 2.0 that was presented in [D5.4]. The present deliverable includes both the specification, as well as the implementation details for the described components. The description of the features of the new functionalities is provided based on the motivating scenarios and the subsequent functional requirements. The focus and the high-level objective of the new services is the provision of improved scalability and modularity properties on the existing services, as well as improved management abilities upon conceptualizations. The implementation of the services is described by providing the related services signatures, their proper way of use, the accepted input parameters, as well as their preconditions and effects. Initially, we describe the Delete Service, which is a Knowledge Repository service allowing the removal of existing namespaces from the repository; such removal includes the deletion of the contents of said namespaces, as well as the deletion of any reference to the namespaces themselves that exists in the repository. This new service enhances SWKM management capabilities upon conceptualizations. Then, the Named Graphs functionality is described, which is a new feature that allows a very flexible modularization of the information found in RDF KBs. We describe in detail the semantics of this feature, as well as the offered capabilities for querying and updating RDF KBs that include modularization information (i.e., information on named graphs) and the implications from their use. Finally, in the context of the Knowledge Mediator, we present the Persistent Comparison Service, which is a variation of the existing (Main Memory) Comparison Service (see M24 release, [D5.3], [D5.4]); unlike the original version, the new service works exclusively on the persistent storage, guaranteeing improved scalability features