16 research outputs found
Optimal design and operation of hybrid AC/DC microgrids towards more resilient energy systems
No full textHumanity has recently embarked on an ambitious journey to decarbonise the world in an effort to reverse the adverse effects of the practices deployed the past two centuries, which have led us to a serious climate change. Regulation and policy have been introduced by countries worldwide to encourage, promote and compensate these efforts, including the UK’s recent announcement pledging to be the first major economy eliminating their contribution to carbon emissions. A comprehensive framework for coordinating actions to reduce CO2 emissions is expected to be put forward addressing the challenges arising, including a significant transformation of the energy system, a restructuring of the energy market and a new way of engaging with the wider public to making what is conceptually significant, perceptually prominent.
Within this context, the concepts of smart grids and, in a smaller scale, microgrids have arisen to assist these decarbonisation efforts. Microgrids have a great potential to actively contribute to grid health status, however the current practices in network design and operation hinder the capabilities of these types of networks. In fact, they do not allow microgrids to realise their potential and enable a paradigm shift in delivering resilience and security of supply from redundancy in network assets and preventive control to a more intelligent operation at the distribution level through corrective control actions. This thesis proposes innovative design and operational models for microgrids, and particularly hybrid AC/DC microgrids, that optimise the total system cost while satisfying pre-specified resilience targets. The modelling framework introduced comprises of a tailor-made genetic algorithm (i.e. for optimal sizing) combined with a detailed AC optimal power flow (OPF) that captures the technical characteristics of both the AC and DC subgrids with an extensive set of technologies considered. The proposed approach, being able to capture technical characteristics such as voltage and frequency through a detailed power flow algorithm, provides accurate solutions and therefore can meaningfully address operational challenges of microgrids. Its capability to additionally capture contingencies ensures that the proposed sizing solutions are suitable both during normal operation and transient states. Finally, the genetic algorithm provides convergence of the model with relative computational simplicity, which is why it has been particularly developed for the needs of this thesis. An innovative Dynamic Stability Constrained OPF is proposed as an extension that incorporates differential equations, such as the swing equation, characterising the operation of power systems. This is achieved via appropriate conversion of the equations to numerically-equivalent algebraic equations. This novel aspect will enable optimal decisions to be taken considering stability properties, which are undeniably necessary in the context of energy systems with renewable penetration of above 50% and are proven to significantly impact the system cost.
Resilience is also central to this thesis, hence it is discussed and limitations of current research typically confusing resilience with reliability are identified. Subsequently, a definition to help the industry merge towards a common understanding and a way of quantifying resilience (particularly relevant to microgrids) are proposed.
As a last step, this thesis identifies the imminent digitalisation energy systems are undergoing and utilising its merits, it introduces a strategy for interaction between distribution networks (incorporating microgrids as one type of resource) and transmission systems with the focus being on exchange of voltage support services. The operational models developed in this thesis could prove to be useful towards optimising the portfolio of assets to provide the services required.Open Acces
DC voltage control for fault management in HVDC system
No full textThis paper focuses on the transmission system options for connection of offshore wind farms and investigates the advantages and disadvantages of proposed concepts in order to draw a conclusion regarding their suitability for connection in the electricity system. Then, the most appropriate solution is implemented in Matlab/Simulink to show its benefits. For this purpose, 5 wind farms are connected to an offshore station and their power output is transferred onshore via a point – to – point DC link. Additionally a novel proposal of DC voltage control is included in the model to simulate the behaviour of the system when faults occur in the electricity grid
Trust & Fair Resource Allocation in Community Energy Systems
No full textThe energy sector faces numerous challenges, including rising electricity costs and inconsistent services due to network overload, often requiring the involvement of a central network operator to address these issues. However, a user-centric approach that prioritizes demand-side management, exemplified by decentralized Community Energy Systems (dCES), presents a promising solution to energy distribution and supply network challenges. dCES can be conceptualized as a small-scale, dynamic distribution network seamlessly integrated into the broader framework of the Smart Grid. In this paradigm, prosumers play an active role, as they must contribute to and draw from a shared energy resource pool, with the overarching goal of avoiding depletion. Specifically, various individuals with different energy consumption patterns and preferences work together to solve collective action problems, i.e., blackouts. Motivated firstly by fair resource allocation, and secondly by the idea that trust is a crucial factor for successful collective action among diverse individuals, we developed a suitable Multi-Agent System (MAS) for dCES to prevent resource depletion. Our experimental results show that introducing trust into dCES can lead to successful collective action, resulting in stable energy networks
Utilization of an Urban AC Microgrid for Improving Voltages Across a Distribution System
No full textA Planning Model for a Hybrid AC–DC Microgrid Using a Novel GA/AC OPF Algorithm
No full textThis paper focuses on developing an appropriate combinatorial optimization technique for solving the optimal sizing problem of hybrid AC/DC microgrids. A novel two-stage iterative approach is proposed. In the first stage, a metaheuristic technique based on a tailor-made genetic algorithm is used to tackle the optimal sizing problem, while, in the second, a non-linear solver is deployed to solve the operational problem subject to the obtained design/investment decisions. The proposed approach, being able to capture technical characteristics such as voltage and frequency through a detailed power flow algorithm, provides accurate solutions and therefore can address operational challenges of microgrids. Its capability to additionally capture contingencies ensures that the proposed sizing solutions are suitable both during normal operation and transient states. Finally, the genetic algorithm provides convergence of the model with relative computational simplicity. The proposed model is applied to a generalizable microgrid comprising of AC and DC generators and loads, as well as various types of storage technologies in order to demonstrate the benefits. The load and natural resources data correspond to real data
Analysis of a wind farm with doubly fed induction generator based wind turbines interconnected to the grid
No full text123 σ.Η αυξανόμενη χρήση της αιολικής ενέργειας στη σημερινή εποχή σε συνδυασμό με τη ραγδαία ανάπτυξη των τεχνολογιών ανεμογεννητριών έχει προκαλέσει το έντονο ενδιαφέρον για τη βέλτιστη αξιοποίηση του ανέμου σε ευρύ φάσμα ταχυτήτων. Στο πλαίσιο αυτό, βασική απαίτηση των αιολικών συστημάτων αποτελεί η αδιάλλειπτη παροχή μέγιστης ισχύος στο ηλεκτρικό δίκτυο ακόμα και σε συνθήκες διαταραχών.
Στόχος της παρούσας διπλωματικής εργασίας είναι η ανάπτυξη κατάλληλου μοντέλου για την ανάλυση και τον έλεγχο ασύγχρονης γεννήτριας διπλής τροφοδότησης, που είναι πλέον πολύ διαδεδομένη στα αιολικά συστήματα. Αρχικά, περιγράφονται τα επιμέρους υποσυστήματα της ανεμογεννήτριας που μελετήθηκε. Συγκεκριμένα, γίνεται αναφορά στο αεροδυναμικό μέρος, αναλύεται μαθηματικά η ασύγχρονη γεννήτρια διπλής τροφοδότησης και επεξηγείται η λειτουργία του back – to – back μετατροπέα με λεπτομερή ανάλυση των επιμέρους τμημάτων του.
Στη συνέχεια, εξετάζεται το σύστημα ελέγχου και ο τρόπος λειτουργίας του. Στο σημείο αυτό, περιγράφεται η τεχνική του διανυσματικού ελέγχου και αναλύεται ο έλεγχος της ανεμογεννήτριας τόσο από την πλευρά του δρομέα όσο και από την πλευρά του δικτύου. Ακόμη, περιγράφεται η λειτουργία του συστήματος ανεύρεσης σημείου παροχής μέγιστης ισχύος με δεδομένη χαρακτηριστική καμπύλη.
Παρουσιάζονται τα χαρακτηριστικά αιολικού πάρκου και μελετώνται διάφορες περιπτώσεις λειτουργίας ώστε να αξιολογηθεί η εναρμόνισή του με τις τεχνικές απαιτήσεις του διαχειριστή του ελληνικού συστήματος. Στο πλαίσιο αυτό, προσομοιώνονται περιπτώσεις κανονικής λειτουργίας αλλά και διαταραχών στην πλευρά του δικτύου.
Επιπλέον, συγκρίνονται οι αποκρίσεις του συστήματος της παρούσας εργασίας με εκείνες αντίστοιχου συστήματος της βιβλιογραφίας, προκειμένου να επιβεβαιωθεί η ακρίβεια των αποτελεσμάτων του προτεινόμενου μοντέλου.
Τέλος, διερευνάται η επίπτωση στις αποκρίσεις του συστήματος ελέγχου με τυπικά κέρδη ανάδρασης ολοκληρωτικού σφάλματος με εκείνες που προκύπτουν μετά από βελτιστοποίησή τους με τη μέθοδο των Ziegler – Nichols.The fast development of wind energy in the current era combined with the rapid improvement of wind turbine technology has attracted the interest to optimize their use in wide wind speed ranges. In this context, an essential requirement for wind turbine systems is the uninterrupted supply of maximum power to the grid even under fault conditions.
The aim of this thesis is the development of appropriate simulation models for analysis and control of doubly fed asynchronous generators, which are now widely used in wind systems. In a first step, the subsystems of the studied wind turbines are described. More specifically, the aerodynamic part of a wind turbine is examined, the doubly fed asynchronous generator is analyzed and the operation of the back – to – back converter is explained while the constitutive parts are detailed.
In a second step, the control and its operating characteristics are examined. At this point, the vector control technique is described while the control actions of the wind turbine are analyzed both at the rotor side and at the grid side. The maximum power point tracking system (MPPT) based on a specific optimum power-speed characteristic is also described.
In the followings, a wind farm is simulated under various operating conditions in order to assess fulfillment of the technical requirements of the Greek system administrator. In this context, both normal operating conditions as well as fault cases at the grid side are examined.
Moreover, the response results of the studied grid interconnected wind farm system are compared to the corresponding ones of a system found in the literature, in order to validate the proposed model accuracy.
Finally, the impact on the controller efficiency is examined when tuning the PI feedback gains by using the Ziegler – Nichols optimization technique.Αναστάσιος Δ. Ουλής-Ρούση
Analytical Framework for Coordinated Planning and Operation of Multicarrier Energy Systems
No full textLocal multicarrier energy systems (MCESs) offer a unique opportunity to exploit the synergies from the interplay of multiple energy carriers and utilize local renewables, thus increasing energy efficiency and supply reliability as well as reducing dependencies from the external networks. To make them sustainable not only from the energy and environmental perspective but also from the economic one and have a concrete option to the centralized energy systems based on fossil fuels, coordinated planning and operation on multiple time horizons is extremely important. This chapter covers all the transversal aspects related to this issue, by presenting a detailed analytical framework for the optimal design and operation of MCESs. First, the chapter presents the modeling of a wide range of generation, conversion, and storage technologies that can be part of MCESs. Then, the optimization frameworks for the design and the operation problems are established, by presenting several types of objective functions, constraints, and solution methodologies. The analytical frameworks are structured by covering different time horizons from long-term system planning to day-ahead and real-time operation. The effectiveness of the tools proposed to address each of these phases will be proved with a proper case study and discussion of simulation results. In addition, a critical overview of the current commercial tools available for the optimal design and operation of MCESs will be presented, by mapping them according to several criteria such as type, type of users, coverage of multicarrier aspects, objective functions, functionalities, mathematical approach, temporal resolution, and time horizons as well as pros and cons in their application to MCESs.©2024 Wiley. This is the peer reviewed version of the following article: Di Somma, M., Papadimitriou, C., Rousis, A. O., Patsidis, A., Shafie‐Khah, M., Shahbazbegian, V. & Askeland, M. (2024). Analytical Framework for Coordinated Planning and Operation of Multicarrier Energy Systems. In M. Di Somma, C. Papadimitriou, G. Graditi, & K. Kok (Eds.). Integrated Local Energy Communities: From Concepts and Enabling Conditions to Optimal Planning and Operation (pp. 187-224). Wiley-VCH Verlag, which has been published in final form at https://doi.org/10.1002/9783527843282.ch6. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions. This article may not be enhanced, enriched or otherwise transformed into a derivative work, without express permission from Wiley or by statutory rights under applicable legislation. Copyright notices must not be removed, obscured or modified. The article must be linked to Wiley’s version of record on Wiley Online Library and any embedding, framing or otherwise making available the article or pages thereof by third parties from platforms, services and websites other than Wiley Online Library must be prohibited.fi=vertaisarvioitu|en=peerReviewed
Design of a hybrid AC/DC microgrid using HOMER Pro : case study on an islanded residential application
No full textThis paper is concerned with the design of an autonomous hybrid alternating current/direct current (AC/DC) microgrid for a community system, located on an island without the possibility of grid connection. It is comprised of photovoltaic (PV) arrays and a diesel generator, AC loads, and battery energy storage devices for ensuring uninterruptible power supply during prolonged periods of low sunshine. A multi-objective, non-derivative optimisation is considered in this residential application; the primary objective is the system cost minimisation, while it is also required that no load shedding is allowed. Additionally, the CO2 emissions are calculated to demonstrate the environmental benefit the proposed system offers. The commercial software, HOMER Pro, is utilised to identify the least-cost design among hundreds of options and simultaneously satisfy the secondary objective. A sensitivity analysis is also performed to evaluate design robustness against the uncertainty pertaining to fuel prices and PV generation. Finally, an assessment of the capabilities of the utilised optimisation platform is conducted, and a theoretical discussion sheds some light on the proposal for an enhanced design tool addressing the identified issues
Enhanced DC voltage control strategy for fault management of a VSC-HVDC connected offshore wind farm
No full textThis paper proposes a DC voltage control strategy for fault management taking into advantage the operation of the master controller located in the offshore AC substation platform. The issue resolved via the proposed controller relates to over-voltages caused in the HVDC links when the power transfer onshore is disrupted due to faults occurring at the AC side of the onshore grid. The control strategy presented in this paper proposes an effective way of maintaining the DC over-voltage within safety limits via reducing the connected wind farm power output. The operation of the aforementioned control strategy requires small computational power and no communication
