In recent years there has been a large increase in the connection of photovoltaic generators to the low voltage distribution network in urban residential areas. In the future, it is predicted that this trend will continue and be accompanied with a rise in the uptake and connection of electric vehicles and heat pumps. Recently, monitoring trials have found widespread current unbalance in the feeders that transmit electrical energy to and from these urban residential areas. This unbalance is likely to be accentuated by the gradual and piecemeal uptake of the aforementioned devices. The combined impact of the changes and present day unbalance is likely to be more frequent thermal and voltage constraint violations unless new strategies are adopted to manage the flow of electrical energy. Here, a novel device named the 'phase switcher' that has no customer compliance requirements is proposed as a new tool for distribution network operators to manage the thermal and voltage constraints of cables. The phase switcher is shown to unlock cable ampacity and maximise voltage headroom and it achieves this through phase balancing in real time. A centralised local feeder controller is simulated to employ dynamic and scheduled phase switcher control algorithms on a real network model, and it's ability to unlock cable ampacity and reduce cable losses is quantified. Also, a small model based controller algorithm is presented and shown to perform almost as well as others despite having a very limited sensing and communication system requirement. Phase switchers are also quantified for their ability to increase feeder voltage headroom when employed to improve the balance of photovoltaic distributed generators across phases. To this end, an exhaustive offline photovoltaic capacity prediction technique is documented which shows that when phase switchers are placed explicitly to a known photovoltaic installation scenario, an almost linear relationship exists between the penetration level and maximum node voltage when PSs or phase conductor rejointing is considered as an option for implementation. Finally, a fast feeder assessment algorithm is detailed that is found to be better and more robust at estimating extreme maximum and minimum photovoltaic penetration level scenarios that cause over-voltage. All the work is presented within a new general mathematical framework that facilitates formulation of the problem and calculation of device phase connections for networks containing phase switchers.

The monitoring and control of low voltage distribution grids has historically been disregarded due to the unidirectional flow of power. However, nowadays the massive integration of distributed energy resources into distribution grids, such as solar photovoltaics, distributed storage, electric vehicles and demand response programs, presents some challenges. For instance, the unidirectional top-down power flow is being replaced by power flows in any direction: top-down and bottom-up. This paradigm shift adds extra regulatory, economic, and technical complexity for the Distribution System Operators (DSO). Thus to overcome the possible operational constraints, thermal limits, or voltage problems in the grid, an update of the existing electricity infrastructures is required. In response to this new situation, this thesis investigates the cost-effective communication and control architectures that are required for active low voltage grid monitoring and control applications, considering the regulatory constraints and the efficient utilization of the assets from a DSO’s perspective. The solutions include: i) optimal sensor placement configuration to perform low voltage state estimation, ii) optimal metering infrastructure designs for active low voltage monitoring applications, iii) coordinated control strategies to allow the integration of microgrid-like structures into the distribution grids, iv) optimal placement of actuators for operating the control strategies, v) a multiagent-based control solution for self-healing and feeder reconfiguration applications, and vi) a framework model and simulations to assess the reliability of the ICT infrastructure that enables the monitoring and control applications. As concluding remark, since the deployment of technology at low voltage grids is restricted to assets owned by the DSO, the operability of the grid is limited. This condition makes it so that the required communication and control enhancement solutions shall prioritize cost-effectiveness over comprehensiveness and complexity. Thus, the results from the presented studies show that it is essential to perform thorough cost-benefit analyses of the potential improvement solutions for each grid, because this will allow deploying the right technology only at the necessary locations. / <p>QC 20171106</p><p></p>

This thesis is focused on demonstrating the impact of the implementation of decentralized distributed energy sources (mainly RES) and electromobility technologies to electrical parameters in Czech medium voltage distribution network. Thesis is divided into two main chapters. First one is a brief theoretical summary of this problematic and the second one is a practical software simulation on a real medium voltage network. Proposed implementation scenarios are based on EU and national strategic plans for time period from 2020 to 2040.

Este trabalho trata do UPFC (Unified Power Flow Controller), que corresponde a um dos mais promissores dispositivos FACTS de última geração, pois apresenta a capacidade de controle independente de todos os parâmetros básicos do sistema elétrico de potência (tensão, impedância e ângulo de fase). Com base nos modelos já propostos para representação deste equipamento em regime permanente, é realizada análise e proposta de um modelo que permite uma abordagem prática, para simulação do UPFC em softwares de fluxo de potência comerciais que não possuem modelos dedicados para este dispositivo. São revisitados os conceitos associados ao UPFC, com apresentação dos modelos analisados e seus respectivos parâmetros, assim como os equipamentos instalados e estimativa de custos para implantação. Através de simulações utilizando o modelo de transformador ideal associado à impedância do transformador série e compensador estático, são obtidos os parâmetros para o modelo de injeção de potências e realizadas simulações que demonstram a equivalência entre estes modelos. Finalmente, é realizada a análise de aplicação do UPFC em um sistema de distribuição de alta tensão, onde há forte presença de geração distribuída com sua sazonalidade característica e linhas que realizam a interligação entre diferentes fontes do sistema, havendo a necessidade de controle do fluxo de potência e melhoria dos níveis de tensão em função dos critérios técnicos e aspectos regulatórios. / This work is about UPFC which corresponds to one of the most promising last generation FACTS device, for it presents independent control in all basic parameters of the electrical power system (voltage, impedance and phase angle). Based on models that have already been proposed to represent this equipment in steady state, an analysis has been made and a model that permits practical approach is proposed to simulate the UPFC in commercial power flow softwares that do not yet support this device. The associated UPFC concepts are revisited with the presentation of analyzed models and their respective parameters as well as the installed equipments and cost estimate for implementation. Through simulations using ideal transformer associated to the series transformer impedance and static Var compensator model, parameters are obtained for the power injection model and simulations were run that showed a similarity between these models. Finally, a UPFC application analysis was done for a region of high voltage distribution system, where there is a strong presence of distributed generation typically seasonal and lines which connect different sources of the system, having the necessity of controlling the power flow and improvement of the voltage levels due to the technical criteria and regulatory aspects.

Este trabalho trata do UPFC (Unified Power Flow Controller), que corresponde a um dos mais promissores dispositivos FACTS de última geração, pois apresenta a capacidade de controle independente de todos os parâmetros básicos do sistema elétrico de potência (tensão, impedância e ângulo de fase). Com base nos modelos já propostos para representação deste equipamento em regime permanente, é realizada análise e proposta de um modelo que permite uma abordagem prática, para simulação do UPFC em softwares de fluxo de potência comerciais que não possuem modelos dedicados para este dispositivo. São revisitados os conceitos associados ao UPFC, com apresentação dos modelos analisados e seus respectivos parâmetros, assim como os equipamentos instalados e estimativa de custos para implantação. Através de simulações utilizando o modelo de transformador ideal associado à impedância do transformador série e compensador estático, são obtidos os parâmetros para o modelo de injeção de potências e realizadas simulações que demonstram a equivalência entre estes modelos. Finalmente, é realizada a análise de aplicação do UPFC em um sistema de distribuição de alta tensão, onde há forte presença de geração distribuída com sua sazonalidade característica e linhas que realizam a interligação entre diferentes fontes do sistema, havendo a necessidade de controle do fluxo de potência e melhoria dos níveis de tensão em função dos critérios técnicos e aspectos regulatórios. / This work is about UPFC which corresponds to one of the most promising last generation FACTS device, for it presents independent control in all basic parameters of the electrical power system (voltage, impedance and phase angle). Based on models that have already been proposed to represent this equipment in steady state, an analysis has been made and a model that permits practical approach is proposed to simulate the UPFC in commercial power flow softwares that do not yet support this device. The associated UPFC concepts are revisited with the presentation of analyzed models and their respective parameters as well as the installed equipments and cost estimate for implementation. Through simulations using ideal transformer associated to the series transformer impedance and static Var compensator model, parameters are obtained for the power injection model and simulations were run that showed a similarity between these models. Finally, a UPFC application analysis was done for a region of high voltage distribution system, where there is a strong presence of distributed generation typically seasonal and lines which connect different sources of the system, having the necessity of controlling the power flow and improvement of the voltage levels due to the technical criteria and regulatory aspects.

Το θέμα της παρούσας διπλωματικής εργασίας είναι η μελέτη της συμπεριφοράς απαγωγέων υπερτάσεων (SPD), όταν αυτοί αποτελούν μέρος του εσωτερικού συστήματος αντικεραυνικής προστασίας για μια οικιακή εγκατάσταση. Αρχικά γίνεται μια αναφορά στα αίτια δημιουργίας κρουστικών υπερτάσεων στο δίκτυο διανομής, ενώ στη συνέχεια δίνεται έμφαση στις υπερτάσεις που προκαλούνται από άμεσα ή έμμεσα κεραυνικά πλήγματα στο σύστημα. Στα πλαίσια της μελέτης δημιουργήθηκε ένα μοντέλο προσομοίωσης που αναπαριστά ένα δίκτυο χαμηλής τάσης TN-C-S με δύο πανομοιότυπους οικιακούς καταναλωτές, όσον αφορά τη δομή της εσωτερικής ηλεκτρικής εγκατάστασής τους παρουσία ή μη διατάξεων αντικεραυνικής προστασίας. Σκοπός της προκειμένης μελέτης είναι να δειχθεί η βέλτιστη συνδεσμολογία των διατάξεων προστασίας μέσα σε εσωτερικές ηλεκτρικές εγκαταστάσεις έτσι ώστε να αποτρέπεται η ανάπτυξη επικίνδυνων τάσεων και ρευμάτων για τον άνθρωπο και τον εξοπλισμό της οικιακής εγκατάστασης. / The subject of this project is a study upon the dynamic performance of surge arresters as a part of the internal lightning protection system for a residential electrical installation. At first, a reference about the actions or the natural phenomena that cause surge overvoltages in low voltage systems is given in detail and is followed by an essential theoretical approach on the lighning phenomenon. Both the causes, the consequences and the conditions in which a lightning occurs are being analysed. Furthermore, the characteristics and the qualifications a Lightning Protection System needs to comply with, are given, according to the Greek Standard ΕΛΟΤ-1197 and the European Standards IEC 62305-2, IEC 61643-12. Along with writing this essay, a simulation model using Simulink-Matlab was produced. The model represents a LV TN-C-S system that distributes power to two households with identical internal electrical installation. The aim of the present study is to indicate the optimal connection of the surge protective devices (SPDs) in the domestic electrical installation in order to prevent the appearance of potentially dangerous overvoltages to the humans or to the household equipment.

This paper deals with possible ways of voltage regulation. Theoretical part includes a search of published methods and the available voltage regulators. Acquired theoretical knowledge has been applied in the development of mathematical models of two selected controllers applied to the testing network. The result of this work is a summary of the outcomes of dynamic simulations with two selected regulators at various locations in testing network. Comparing the results of dynamic simulation for two selected states was chosen the most appropriate regulator and its optimal location in testing network.

[ES] La gran mayoría de procesos del mundo real tienen incertidumbres inherentes, las cuales, al ser consideradas en el proceso de modelado, se puede obtener una representación que describa con la mayor precisión posible el comportamiento del proceso real. En la mayoría de casos prácticos, se considera que éstas tienen un comportamiento estocástico y sus descripciones como distribuciones de probabilidades son conocidas. Las estrategias de MPC estocástico están desarrolladas para el control de procesos con incertidumbres de naturaleza estocástica, donde el conocimiento de las propiedades estadísticas de las incertidumbres es aprovechado al incluirlo en el planteamiento de un problema de control óptimo (OCP). En éste, y contrario a otros esquemas de MPC, las restricciones duras son relajadas al reformularlas como restricciones de tipo probabilísticas con el fin de reducir el conservadurismo. Esto es, se permiten las violaciones de las restricciones duras originales, pero tales violaciones no deben exceder un nivel de riesgo permitido. La no-convexidad de tales restricciones probabilísticas hacen que el problema de optimización sea prohibitivo, por lo que la mayoría de las estrategias de MPC estocástico en la literatura se diferencian en la forma en que abordan tales restricciones y las incertidumbres, para volver el problema computacionalmente manejable. Por un lado, están las estrategias deterministas que, fuera de línea, convierten las restricciones probabilísticas en unas nuevas de tipo deterministas, usando la propagación de las incertidumbres a lo largo del horizonte de predicción para ajustar las restricciones duras originales. Por otra parte, las estrategias basadas en escenarios usan la información de las incertidumbres para, en cada instante de muestreo, generar de forma aleatoria un conjunto de posibles evoluciones de éstas a lo largo del horizonte de predicción. De esta manera, convierten las restricciones probabilísticas en un conjunto de restricciones deterministas que deben cumplirse para todos los escenarios generados. Estas estrategias se destacan por su capacidad de incluir en tiempo real información actualizada de las incertidumbres. No obstante, esta ventaja genera inconvenientes como su gasto computacional, el cual aumenta conforme lo hace el número de escenarios y; por otra parte, el efecto no deseado en el problema de optimización, causado por los escenarios con baja probabilidad de ocurrencia, cuando se usa un conjunto de escenarios pequeño. Los retos mencionados anteriormente orientaron esta tesis hacia los enfoques de MPC estocástico basado en escenarios, produciendo tres contribuciones principales. La primera consiste en un estudio comparativo de un algoritmo del grupo determinista con otro del grupo basado en escenarios; se hace un especial énfasis en cómo cada uno de estos aborda las incertidumbres, transforma las restricciones probabilísticas y en la estructura de su OCP, además de señalar sus aspectos más destacados y desafíos. La segunda contribución es una nueva propuesta de algoritmo MPC, el cual se basa en escenarios condicionales, diseñado para sistemas lineales con incertidumbres correlacionadas. Este esquema aprovecha la existencia de tal correlación para convertir un conjunto de escenarios inicial de gran tamaño en un conjunto de escenarios más pequeño con sus probabilidades de ocurrencia, el cual conserva las características del conjunto inicial. El conjunto reducido es usado en un OCP en el que las predicciones de los estados y entradas del sistema son penalizadas de acuerdo con las probabilidades de los escenarios que las componen, dando menor importancia a los escenarios con menores probabilidades de ocurrencia. La tercera contribución consiste en un procedimiento para la implementación del nuevo algoritmo MPC como gestor de la energía en una microrred en la que las previsiones de las energías renovables y las cargas están correlacionadas. / [CA] La gran majoria de processos del món real tenen incerteses inherents, les quals, en ser considerades en el procés de modelatge, es pot obtenir una representació que descriga amb la major precisió possible el comportament del procés real. En la majoria de casos pràctics, es considera que aquestes tenen un comportament estocàstic i les seues descripcions com a distribucions de probabilitats són conegudes. Les estratègies de MPC estocàstic estan desenvolupades per al control de processos amb incerteses de naturalesa estocàstica, on el coneixement de les propietats estadístiques de les incerteses és aprofitat en incloure'l en el plantejament d'un problema de control òptim (OCP). En aquest, i contrari a altres esquemes de MPC, les restriccions dures són relaxades en reformulades com a restriccions de tipus probabilístiques amb la finalitat de reduir el conservadorisme. Això és, es permeten les violacions de les restriccions dures originals, però tals violacions no han d'excedir un nivell de risc permès. La no-convexitat de tals restriccions probabilístiques fan que el problema d'optimització siga computacionalment immanejable, per la qual cosa la majoria de les estratègies de MPC estocàstic en la literatura es diferencien en la forma en què aborden tals restriccions i les incerteses, per a tornar el problema computacionalment manejable. D'una banda, estan les estratègies deterministes que, fora de línia, converteixen les restriccions probabilístiques en unes noves de tipus deterministes, usant la propagació de les incerteses al llarg de l'horitzó de predicció per a ajustar les restriccions dures originals. D'altra banda, les estratègies basades en escenaris usen la informació de les incerteses per a, en cada instant de mostreig, generar de manera aleatòria un conjunt de possibles evolucions d'aquestes al llarg de l'horitzó de predicció. D'aquesta manera, converteixen les restriccions probabilístiques en un conjunt de restriccions deterministes que s'han de complir per a tots els escenaris generats. Aquestes estratègies es destaquen per la seua capacitat d'incloure en temps real informació actualitzada de les incerteses. No obstant això, aquest avantatge genera inconvenients com la seua despesa computacional, el qual augmenta conforme ho fa el nombre d'escenaris i; d'altra banda, l'efecte no desitjat en el problema d'optimització, causat pels escenaris amb baixa probabilitat d'ocurrència, quan s'usa un conjunt d'escenaris xicotet. Els reptes esmentats anteriorment van orientar aquesta tesi cap als enfocaments de MPC estocàstic basat en escenaris, produint tres contribucions principals. La primera consisteix en un estudi comparatiu d'un algorisme del grup determinista amb un altre del grup basat en escenaris; on es fa un especial èmfasi en com cadascun d'aquests aborda les incerteses, transforma les restriccions probabilístiques i en l'estructura del seu problema d'optimització, a més d'assenyalar els seus aspectes més destacats i desafiaments. La segona contribució és una nova proposta d'algorisme MPC, el qual es basa en escenaris condicionals, dissenyat per a sistemes lineals amb incerteses correlacionades. Aquest esquema aprofita l'existència de tal correlació per a convertir un conjunt d'escenaris inicial de gran grandària en un conjunt d'escenaris més xicotet amb les seues probabilitats d'ocurrència, el qual conserva les característiques del conjunt inicial. El conjunt reduït és usat en un OCP en el qual les prediccions dels estats i entrades del sistema són penalitzades d'acord amb les probabilitats dels escenaris que les componen, donant menor importància als escenaris amb menors probabilitats d'ocurrència. La tercera contribució consisteix en un procediment per a la implementació del nou algorisme MPC com a gestor de l'energia en una microxarxa en la qual les previsions de les energies renovables i les càrregues estan correlacionades. / [EN] The vast majority of real-world processes have inherent uncertainties, which, when considered in the modelling process, can provide a representation that most accurately describes the behaviour of the real process. In most practical cases, these are considered to have stochastic behaviour and their descriptions as probability distributions are known. Stochastic model predictive control algorithms are developed to control processes with uncertainties of a stochastic nature, where the knowledge of the statistical properties of the uncertainties is exploited by including it in the optimal control problem (OCP) statement. Contrary to other model predictive control (MPC) schemes, hard constraints are relaxed by reformulating them as probabilistic constraints to reduce conservatism. That is, violations of the original hard constraints are allowed, but such violations must not exceed a permitted level of risk. The non-convexity of such probabilistic constraints renders the optimisation problem computationally unmanageable, thus most stochastic MPC strategies in the literature differ in how they deal with such constraints and uncertainties to turn the problem computationally tractable. On the one hand, there are deterministic strategies that, offline, convert probabilistic constraints into new deterministic ones, using the propagation of uncertainties along the prediction horizon to tighten the original hard constraints. Scenario-based approaches, on the other hand, use the uncertainty information to randomly generate, at each sampling instant, a set of possible evolutions of uncertainties over the prediction horizon. In this fashion, they convert the probabilistic constraints into a set of deterministic constraints that must be fulfilled for all the scenarios generated. These strategies stand out for their ability to include real-time updated uncertainty information. However, this advantage comes with inconveniences such as computational effort, which grows as the number of scenarios does, and the undesired effect on the optimisation problem caused by scenarios with a low probability of occurrence when a small set of scenarios is used. The aforementioned challenges steered this thesis toward stochastic scenario-based MPC approaches, and yielded three main contributions. The first one consists of a comparative study of an algorithm from the deterministic group with another one from the scenario-based group, where a special emphasis is made on how each of them deals with uncertainties, transforms the probabilistic constraints and on the structure of the optimisation problem, as well as pointing out their most outstanding aspects and challenges. The second contribution is a new proposal for a MPC algorithm, which is based on conditional scenarios, developed for linear systems with correlated uncertainties. This scheme exploits the existence of such correlation to convert a large initial set of scenarios into a smaller one with their probabilities of occurrence, which preserves the characteristics of the initial set. The reduced set is used in an OCP in which the predictions of the system states and inputs are penalised according to the probabilities of the scenarios that compose them, giving less importance to the scenarios with lower probabilities of occurrence. The third contribution consists of a procedure for the implementation of the new MPC algorithm as an energy manager in a microgrid in which the forecasts of renewables and loads are correlated. / González Querubín, EA. (2024). Scenario-Based Model Predictive Control for Systems with Correlated Uncertainties [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/203887