There is a growing interest in electric transportation, and the number of electric vehicles (EVs) is increasing. The resulting increase in EV charging power demand has an adverse impact on the existing power grids, especially the distribution transformers. The repeated and continued overloading caused by EV charging can significantly reduce their operational life. This dissertation aims to comprehensively study the adverse impacts of EV charging on distribution transformers and provide robust and practical solutions to mitigate it. A typical North American secondary distribution system with different EV penetration levels and four realistic residential EV charging scenarios are used for the analyses. The IEEE Standard C57.91-2011 is used to quantify transformer life under different scenarios and to validate the efficacy of the proposed overloading mitigation strategies. It is observed that EV charging can have a significant impact on the life of distribution transformers. To mitigate the impact of EV charging on the distribution transformer, first, a practical solution based on reactive power compensation is proposed. The method is based on reducing the over- all transformer losses by providing a component of the residential reactive power demand through non-unity power factor operation of the EV charger. A centralized recursive control structure is proposed to compute and communicate the required reactive power values to the individual EVs. It is shown that the proposed technique increases the distribution transformer’s life by an average of nearly 47% in all four scenarios considered. Moreover, the proposed controller’s structure makes it effective even on low-bandwidth, high-latency communication networks. To verify this, the proposed controller’s stability under communication delays and its robustness against potential communication failures is also validated. This research also studies potential concerns about the charger’s reliability by non-unity power factor operation. Accordingly, an alternative overloading mitigation strategy is also proposed based on fixed charging current magnitude. This second method is shown to be more effective in reducing transformer overloading at the cost of a marginal decrease in the charging rate. Lastly, a high-level overview of the existing vehicle-to-grid communication standards is presented to provide a better context for practical implementation and identify potential challenges.

Reactive power is critical to reliable operation of the modern AC power system. There is a plethora of motor-loads, transformers, and power-electronic loads connected to the power grid, which consume reactive power for normal operation. Transmission lines also consume reactive power when they are loaded above their surge impedance loading (SIL). Reactive power can exact opportunity cost due to reduced capacity of the lines to carry real power, which in turn lowers revenue. Most transmission owners (TOs) levy large penalties against load serving entities (LSEs), industrial facilities, and other end-use customers, who consume more than their allotted amount, as measured by their power factor. These penalties are to incentivize their customers to meet their reactive power needs locally as well as to recuperate the TOs' financial losses. Harmonic pollution is another factor that prevents the optimal operation of the grid and the connected loads. Harmonics are attributable to proliferation of the diode-rectifier- or thyristor-rectifier-interfaced loads such as variable speed ac drives and power supplies in server farms, electric arc furnaces, and other non-linear loads, which are widely employed by the industrial sector. With wider adoption of harmonic-rich loads by the consumer sector as well, such as HDTVs and compact fluorescent lamps (CFLs), greater level of triplen harmonics associated with single-phase loads are also increasingly seen on the distribution grid. The increasing penetration of renewable resources and electrification of light-duty vehicles are expected to further aggravate the stresses and congestion on the utility grid. Reactive power compensation is necessary for supporting the AC grid and maintaining a healthy voltage stability margin. Compensation can also enhance the utilization of system capacity, lower system losses, provide fault ride-through, and enable a quick fault recovery. Existing VAR and harmonic compensation technologies are either too expensive or inadequate to meet the dynamic needs of the modern and the future power system. This dissertation presents a novel class of Dynamic VAR and Harmonic Compensators (DVHCs) for supplying or absorbing reactive power and providing harmonic filtering, where the compensation is in shunt with the line and the load. The underlying concept is based on augmenting a static or passive component like a capacitor or an inductor with a direct AC converter and imbuing the passive component with dynamic properties. The direct AC converter can be configured as a buck, a boost, or a buck-boost. A `fail-normal' switch is an integral part of the DVHCs that bypasses the converter when it fails, preserving the original functionality and the reliability of the passive component. The DVHCs are modular and scalable such that they can be employed in applications ranging from residential and industrial with voltages less than 480 V, to power distribution level with voltages as high as 35 kV. The Dynamic Inductor (D-IND) and the Dynamic Capacitor (D-CAP) are subclasses of the DVHCs. As the applications for supplying leading VARs are more prevalent, the primary focus of this work is on the buck, the boost, and the buck-boost configurations of the D-CAP. To understand the characteristics and operation of the DVHCs, this work has developed time-domain models for analyzing the transient and dynamic behavior; frequency-domain models for understanding the harmonic interactions and the steady-state relationships between switch duty and current harmonics; and small-signal models for studying the dynamics of the converter due to various perturbations. The small-signal models also enable extraction of transfer functions in designing controllers and assessing stability margins. Control architectures and techniques are presented for effectively controlling the D-CAP when commutating the semiconductor devices with both high and low switching frequencies. In modularly scaling the DVHCs to higher voltages, three medium-voltage topologies are discussed. They are based on series-connecting fractionally-rated devices, AC flying capacitors, and series cascading multiple two-level cells. These implementations allow direct connect to the medium-voltage grid, thereby obviating the use of transformers, and subsequently reducing the losses, cost, complexity, and footprint. A novel AC snubber concept is proposed to provide safe commutation of the AC switches, fault tolerance by managing the energy trapped in parasitics and filters, and to enable dynamic and static voltage sharing when integrated around the series-connected devices. Design equations for selecting and rating the devices and components in the buck, the boost, and the buck-boost configurations of the D-CAP are presented. Three sets of example designs, with one at low-voltage and two at medium-voltage, are discussed to demonstrate the typical size and ratings of the various components under realistic operating conditions. Measurements and the related discussions of a 40 kVA buck D-CAP prototype built to validate the effectiveness of the proposed concepts are presented.

Recent decades have witnessed a significant increment in power contribution from wind generators. This increment in penetration requires power engineers to tackle multi-fold challenges concerning operational and stability aspects. There exists a significant attention among the researchers in analyzing the impact of wind generation on various system aspects. This thesis focuses on steady state voltage stability aspects with penetration of Variable speed wind generators. Traditionally, ancillary services are supplied by large conventional generators. However, with the huge penetration of wind generators as a result of the growing interest in satisfying energy requirements, and considering the benefits that they can bring along to the electrical system and to the environment, it appears reasonable to assume that ancillary services could also be provided by wind generators in an economical and efficient way. Certain types of wind generators can support reactive power for the Power Market. Fixed and Semi-Variable speed wind turbine generators were predominantly employed during the early installations of wind generators. These units require reactive power support from the grid and are usually equipped with capacitor banks to provide the necessary reactive power. Further, STATic synchronous COMpensator (STATCOM) and Static Var Compensator (SVC) with various configurations were proposed to enhance the system operations under normal and disturbed conditions. On the other hand, Variable speed wind turbine generators provide flexibility in control and hence are becoming increasingly popular. Popular among this class of wind turbine generating units are Doubly Fed Induction Generator(DFIG) and induction/synchronous Generator with Front End Converter(GFEC). Contrary to Fixed and Semi-Variable speed wind machines, Variable speed wind turbine generators are capable of providing reactive power to the grid. The converter and control schemes associated with these machines permits controlling the active and reactive power output to desired level. It is possible to control the reactive power output of these machines independently of the active power. Researchers in the past have investigated the impact of reactive power output of variable speed wind machines on system stability. In literature, approaches are proposed to utilize the flexibility in reactive power generation of DFIG to reduce system losses, improve reliability in static and dynamic system operation. Approaches in literature investigate the impact on voltage stability of system by considering the flexibility of reactive power output of wind machine in isolation. However, significant improvement in static voltage stability, voltage profile, system power losses etc. can be attained if the Reactive Power output of Variable Speed wind machines can be properly coordinated with other reactive power controllers. The prime objective of the thesis is to propose algorithms to coordinate the reactive power output of Variable Speed Wind Generators with other reactive power controllers for Enhancement in voltage stability margin, system losses and voltage profiles.

Le travail présenté dans ce mémoire s’est déroulé dans le cadre d’une collaboration entre le groupe Convertisseur Statique du laboratoire LAPLACE et le département " Installations Fixes de Traction Electrique " de la Direction de l’Ingénierie de la SNCF. Aujourd'hui, la majorité du trafic sur le réseau ferré monophasé 25 kV / 50 Hz est assurée par des locomotives équipées de redresseurs contrôlés à thyristors. Du fait de l'augmentation du trafic, l'utilisation de ces locomotives nécessite la mise en place de moyen de compensation de puissance réactive afin de maintenir la tension caténaire à un niveau acceptable et de réduire la facture en énergie réactive. La correction du facteur de déplacement est réalisée en partie par des batteries de compensation fixes dont lapuissance est limitée par la tension maximale admissible à vide sur la caténaire. Afin d’adapter le niveau de compensation à la consommation, la partie fixe est complétée par un dispositif réglable basé sur une réactance contrôlée par des thyristors. Bien qu’il soit simple dans son principe, ce dispositif nécessite un filtrage des harmoniques en basse fréquence avec des circuits LC volumineux. L’objectif de cette thèse est de proposer une nouvelle topologie de compensateur de puissance réactive à haut rendement et utilisant un contrôle à modulation de largeur d’impulsion dans le but de minimiser le volume des éléments de filtrage. La première partie de ce mémoire est consacrée à une étude comparative de différentes topologies du point de vue des pertes dans les semi-conducteurs et du dimensionnement des éléments de filtrage associés. Les résultats de cette étude montrent que les topologies à base de gradateurs MLI, constituent les solutions les plus intéressantes pour réaliser le compensateur. La deuxième partie du travail concerne l’étude de l’insertion d’un compensateur à base de gradateurs MLI sur le réseau ferré avec la prise en compte des interactions harmoniques. Le cas d’étude concerne une sous-station où doit être implantée une compensation variable de 3 MVAR. Un relevé des courants délivrés par la sous-station a été effectué dans le but d’analyser leur contenu harmonique. Une modélisation de la sous-station et du compensateur est ensuite proposée et des simulations temporelles de l’ensemble sont réalisées en prenant en compte les formes d’ondes réelles des courants absorbés par les trains. Finalement, cette étude par simulation permet d’affiner le dimensionnement du compensateur à gradateurs MLI et des éléments de filtrage associés. Elle met en évidence l’avantage d’une solution, avec des gradateurs MLI en montage élévateur de tension, qui fonctionne sans transformateur et réutilise les batteries de compensation fixes déjà installées en sous-station à la fois comme diviseur de tension et éléments de filtrage. Afin de valider le principe de cette nouvelle topologie de compensateur statique de puissance réactive, un démonstrateur de 1,2 MVAR est mis en oeuvre et testé sur une plateforme d'essai de la SNCF. / The work presented in this thesis is the result of collaboration between the Static Converters research group of LAPLACE Laboratory and the department "Installations Fixes de Traction Electrique" of the Engineering Division of the French Railways company, SNCF. Nowadays, most of the traffic in 25 kV – 50 Hz lines is achieved by old locomotives equipped with thyristor rectifiers. As traffic and load increase, reactive power compensation devices are required to keep the overhead line voltage at acceptable level and to reduce the spending for reactive power. The basic power factor correction is completed by fixed compensation banks. But the difficulty of such configuration is the no-load operation of overhead lines. The voltage can increase out of the 29 kV standard limit and to avoid this problem, variable reactive power compensator is often added to the fixed compensation banks. Nowadays, SNCF is equipped with thyristor based static VAR compensators (SVC). The main drawback of this topology is the requirement of a large LC shunt filter tuned for the third harmonic. The goal of this thesis is to find a new high-efficiency topology of STATic COMpensator (STATCOM) using PWM control to minimize the filtering components. The first part of this thesis focuses on a comparative study of different topologies in terms of semiconductor losses and filter elements size. The results of this study show that the topologies based on PWM AC Chopper are the most interesting solutions to achieve the compensator. The second part of the work concerns the influence of the connection of a STATCOM to a substation and focuses on the harmonic interactions with locomotives. The study case concerns a high traffic substation where a 3 MVAR STATCOM should be installed. Substation output current measurement was carried out in order to analyze its harmonic content. Models of the substation and the STATCOM are then proposed and simulations using real current waveforms are performed. Finally, this simulation study helps to refine the features of the AC Chopper topology and its filter elements. It highlights the advantage of a solution, with boost AC Choppers which operate without transformer and reuse the fixed compensation banks already installed in the substation as voltage divider and filter. To validate the principle of this new topology of STATCOM, a 1.2 MVAR prototype is built in LAPLACE laboratory and tested on a SNCF test platform.

The purpose of this investigation is to identify appropriate location of capacitor banks and sources of reactive power by studying power system stability in the vicinity of system equilibrium states. The locations for reactive power sources are determined by identifying those modes of the system that participate most in the system behavior in general and in dictating the final state of the system after experiencing faults or disturbances. To identify the relevant modes of the system that participate most in the system dynamic, we shall make use of modal and participation analysis for different system conditions. We also apply modal and participation analysis to a system in order to identify the components of greatest impact that result in the most efficient system control. The ideas developed in this study are used to analyze and identify weak boundaries of the IEEE 39- Bus system that contribute to the system’s instability.

It is specifically important to focus on voltage stability analysis of the power system to avoid worst case scenarios such as voltage collapse. The purpose of this thesis is to identify methods for enhancing the steady-state voltage stability using FACTS devices and determining their impact on real and reactive power losses, improvement of bus voltage magnitude, and transmission line loadability. To achieve this, FACTS devices such as Static VAR Compensator (SVC), Static Synchronous Compensator (STATCOM), and Thyristor Controlled Series Capacitor (TCSC) are used in the test system as three separate test cases. The results obtained assist in drawing conclusions on the effectiveness of each FACTS devices at generator, load and swing buses, on lines between two load buses, and between a load bus and a generator bus, in terms of metrics such as voltage magnitude profile, PV curves, and active and reactive power losses.

O presente trabalho propõe o desenvolvimento de uma metodologia de valoração da reserva de potência ativa e do suporte de potência reativa a partir de plantas hidroelétricas. Inicialmente foi apresentado um histórico que descreveu o que foi definido e regulamentado sobre estes serviços em diferentes mercados de energia. Em seguida, com o objetivo de valorar o serviço de reserva de potência ativa foi realizada a mensuração da perda de eficiência, resultante do fornecimento deste serviço, que após convertida em MWh foi relacionada à perda de oportunidade, caso essa energia fosse comercializada no mercado de energia. Para a valoração do suporte de potência reativa foi utilizada a teoria de Fluxo de Potência Ótimo com objetivo de minimizar as perdas do sistema e relacionar essa minimização à redução do suporte de potência reativa. Em seguida, foi apresentada uma metodologia de valoração e alocação dos custos do suporte de potência reativa entre as barras responsáveis pela necessidade adicional deste suporte. Foram realizados vários testes para validação e verificação das metodologias propostas. / The present study proposes valuation methodologies for the spinning reserve and for the reactive power support regarding hydroelectric plants. Initially, a revision describing what was defined and regulated on these services in different energy markets is presented. In order to valuate the spinning reserve service, the measurement of efficiency losses stemming from this service supply was done. Thereafter, the efficiency losses were converted into MWh and related to the opportunity loss, in case this energy was commercialized in the energy market. As for the reactive power support valuation, the Optimal Power Flow was used. The objective was to minimize the system losses and relate such a minimization to the reactive power support. Subsequently, methodologies for the reactive power support costs and for the cost allocation among the responsible buses for additional requirement of this support are also presented. Various tests to validate and verify the above mentioned methodologies were carried out.

O presente trabalho propõe o desenvolvimento de uma metodologia de valoração da reserva de potência ativa e do suporte de potência reativa a partir de plantas hidroelétricas. Inicialmente foi apresentado um histórico que descreveu o que foi definido e regulamentado sobre estes serviços em diferentes mercados de energia. Em seguida, com o objetivo de valorar o serviço de reserva de potência ativa foi realizada a mensuração da perda de eficiência, resultante do fornecimento deste serviço, que após convertida em MWh foi relacionada à perda de oportunidade, caso essa energia fosse comercializada no mercado de energia. Para a valoração do suporte de potência reativa foi utilizada a teoria de Fluxo de Potência Ótimo com objetivo de minimizar as perdas do sistema e relacionar essa minimização à redução do suporte de potência reativa. Em seguida, foi apresentada uma metodologia de valoração e alocação dos custos do suporte de potência reativa entre as barras responsáveis pela necessidade adicional deste suporte. Foram realizados vários testes para validação e verificação das metodologias propostas. / The present study proposes valuation methodologies for the spinning reserve and for the reactive power support regarding hydroelectric plants. Initially, a revision describing what was defined and regulated on these services in different energy markets is presented. In order to valuate the spinning reserve service, the measurement of efficiency losses stemming from this service supply was done. Thereafter, the efficiency losses were converted into MWh and related to the opportunity loss, in case this energy was commercialized in the energy market. As for the reactive power support valuation, the Optimal Power Flow was used. The objective was to minimize the system losses and relate such a minimization to the reactive power support. Subsequently, methodologies for the reactive power support costs and for the cost allocation among the responsible buses for additional requirement of this support are also presented. Various tests to validate and verify the above mentioned methodologies were carried out.

No Brasil, quando uma unidade consumidora (UC) sob regime de microgeração ou de minigeração distribuída tem parte ou a totalidade da sua demanda por potência ativa suprida pela planta geradora, mas sua demanda por potência reativa é atendida exclusivamente pela rede elétrica, verifica-se uma aparente deterioração do fator de potência dessa UC, sob a ótica da concessionária. Esse efeito decorre do fato de que o fator de potência, de acordo com a regulamentação vigente, é determinado apenas a partir das medições dos fluxos de potência ativa e reativa trocados entre a UC e a rede elétrica e não também entre a planta geradora e UC. Para consumidores do Grupo A (tensão de fornecimento igual ou superior a 2,3 kV) nessa situação, de acordo com o perfil da carga, pode haver cobrança por excedentes de reativos, constituindo-se assim uma barreira. Especificamente no caso de sistemas fotovoltaicos conectados à rede, existe a possibilidade de se utilizar os próprios inversores c.c.-c.a para suprir a demanda de reativos da UC e, dessa forma, minimizar o problema apresentado. Com o objetivo de se avaliar essa alternativa no contexto brasileiro, tendo-se em vista condições reais de operação e os limites normativos de injeção de potência reativa para inversores de sistemas fotovoltaicos, foi realizado um estudo de caso de uma planta fotovoltaica instalada no telhado do prédio da Administração do Instituto de Energia e Ambiente da Universidade de São Paulo. O estudo mostrou que a compensação realizada por meio do inversor selecionado evitou a cobrança de excedentes de reativos sem afetar de forma significativa a produtividade do sistema fotovoltaico. Do ponto de vista elétrico, verificou-se que a injeção de reativos pelo inversor não provocou variações significativas de tensão no ponto de acoplamento ou no alimentador e, ainda, se verificou considerável liberação de capacidade do sistema supridor da concessionária. Dessa forma, a análise dos resultados indica uma tendência a se considerar a compensação de reativos proporcionada pelo próprio inversor a opção mais viável para se lidar com os excedentes de reativos, comparativamente a métodos convencionais de compensação ou à situação em que nenhuma ação compensatória seja implementada. / In Brazil, when a consumer unit (CU) under a distributed microgeneration or minigeneration scheme has part or all of its demand for active power supplied by the generating plant, but its demand for reactive power is served exclusively by the grid, the power factor of this CU appears deteriorated, from the perspective of the utility. This effect is due to the fact the power factor, according to the current regulations, is determined only from measurements of the flows of active and reactive power exchanged between the UC and the grid and not also between the generating plant and UC. Users of group A (supply voltage equal to or greater than 2.3 kV) in this situation, according to the CU load profile, may be charged due the reactive power excess, thus constituting a barrier. Specifically in the case of grid-connected photovoltaic systems, there is the possibility of using the d.c.- a.c. inverters to suply the CU reactive power demand and, thus, minimizing the presented problem. In order to evaluate this alternative in the Brazilian context, keeping in view real operating conditions and regulatory limits for the reactive power injection for photovoltaic inverters, we conducted a case study with a photovoltaic plant installed on the roof of the University of São Paulo Institute for Energy and Environment administration building. The study showed that the compensation performed by the selected inverter prevented the reactive power excess charging without affecting significantly the photovoltaic system productivity. From an electrical point of view, it was found that the injection of reactive power by the inverter did not cause significant voltage variations at the coupling point or at the transformer and, additionally, there was a significant release in the utility suply system capacity. Thus, the analysis results indicates a tendency to consider the compensation provided by the inverter itself the most viable option for dealing with the surplus of reactive power compared to conventional compensation methods or to the situation in which no compensatory action is implemented.

Ystad Energi har ansvaret över elnätet i Ystads kommun. Med ökande efterfråga om el har samhället blivit sårbart. Därför jobbar myndigheterna och elleverantörer alltid för att säkerställa en trygg och säker elleverans. Variationer i energibehovet under de olika årstider sätter elsystemet i en svår situation gällande elleveranssäkerhet. Ystad Energi har noterat att elnätet matar ut reaktiv effekt mot överliggande nät under sommarperioden. Vilket kan påverka förlusterna och systemets drifttillstånd i både lokal – och regionnät. Därför fokuserar detta arbete på att utföra analyser av reaktiv effekt i nätledningarna som ligger mellan fördelningsstationerna och nätstationerna, d.v.s. i 10.7 kV – nivå av den s.k. distributionsnätet. För att minska elavbrott i systemet på grund av väder och annan yttre påverkan har Ystad Energi grävt ner alla ledningar i nätet. Datainsamlingen från Ystad Energi visar att den reaktiva effektinmatningen ökar mest under sommaren jämfört med andra årstider. Utifrån vetenskapliga teorier och tidigare arbeten anses kablifiering som en viktig orsak till reaktiv effektinmatning i ett elsystem. Datainsamlingen visar även avsevärda variationer i energiförbrukningen mellan vinter- och sommarhalvåret, där energiförbrukningen är mycket lägre under sommaren på grund av klimatet och livsstilen. Därför leder detta till spänningsförhöjning i elnätet som vidare kan leda till kapacitiv reaktiv effektgenerering. I arbetet utförs även analyser på nätet med anslutna produktionsanläggningar såsom vindkraft som kan påverka effektflödet i nätet. Rapporten skall presentera vilka möjliga lösningar som kan vara lämpliga för att minska den reaktiva effekten i nätet. Kraven som ställs från myndigheterna kring reaktiv effekt redovisas även i rapporten. / Ystad Energy is responsible for the power grid in Ystad municipality. With increasing demand for electricity, society has become more vulnerable. Therefore, authorities and electricity suppliers always work to ensure safe and secure electricity supply. Variations in energy demand and climate change put the electrical system in a difficult situation regarding electricity supply safety. Ystad Energy has noted that the power grid has high values of reactive power over a part of year, which may affect the losses and system operating conditions in both local and regional networks. Therefore, this work focuses on performing reactive power analysis in the power cables located between the high voltage substations and the low voltage substations, i.e. in the 10.7 kV level of the distribution network. All overhead lines in Ystad municipality are already buried in the ground to reduce line faults in the system due to weather and other influences. The data collection from Ystad Energy shows that the reactive power input increases most during the summer. Underground cables are considered an important cause that contributes to reactive power input in an electrical system. Data collection also shows significant variations in energy consumption between the winter and summer months, where energy consumption is much lower in the summer due to the climate and human habits. Therefore, this leads to a voltage increase in the mains that can further lead to a capacitive reactive power generation. In the project, an analysis of the power grid has been performed, considering the current grid topology. Simulations of different scenarios with production plants, such as wind power, which can affect the power flow in the network, are also carried out. It was proved that the reactive power in the grid is produced by the underground cables. The report also presents some possible solutions that may be appropriate to reduce the reactive power in the network.