abstract: Traditional approaches to modeling microgrids include the behavior of each inverter operating in a particular network configuration and at a particular operating point. Such models quickly become computationally intensive for large systems. Similarly, traditional approaches to control do not use advanced methodologies and suffer from poor performance and limited operating range. In this document a linear model is derived for an inverter connected to the Thevenin equivalent of a microgrid. This model is then compared to a nonlinear simulation model and analyzed using the open and closed loop systems in both the time and frequency domains. The modeling error is quantified with emphasis on its use for controller design purposes. Control design examples are given using a Glover McFarlane controller, gain sched- uled Glover McFarlane controller, and bumpless transfer controller which are compared to the standard droop control approach. These examples serve as a guide to illustrate the use of multi-variable modeling techniques in the context of robust controller design and show that gain scheduled MIMO control techniques can extend the operating range of a microgrid. A hardware implementation is used to compare constant gain droop controllers with Glover McFarlane controllers and shows a clear advantage of the Glover McFarlane approach. / Dissertation/Thesis / Ph.D. Electrical Engineering 2013

The objective of this dissertation is to carry out dynamic modeling, analysis and control of power systems with Renewable Energy Sources (RES) such as: Photovoltaic (PV) power sources and wind farms. The dissertation work is mainly focused on microgrid since it plays a major role in modern power systems and tend to have higher renewable power penetration. Two main theoretical concepts, dynamic phasor and impedance modeling have been adopted to model and analyze the power systems/mocrogrids with RES. The initial state calculation which is essential for small signal analysis of a system is carried out as the first step of the dissertation work. Dynamic phasor and impedance modeling techniques have been utilized to model and analyze power systems/micogrids as the second phase of the work. This part consists of two main studies. First case investigates the impedance modeling of Thyristor Controller Series Capacitor (TCSC) for sub-synchronous resonance (SSR) analysis where a wind farm is connected to a power system through series compensated line. Second case utilizes the dynamic phasor concept to model a microgrid in unbalanced condition. Here the unbalance is caused by a single phase PV connected to the microgrid. Third Phase of the dissertation work includes upper level control of the microgrid. Here prediction and optimization control for a microgrid with a wind farm, a PV system, an energy storage system and loads is evaluated. The last part of the dissertation work focuses on real time modeling and hardware in loop simulation test bed for microgrid applications. This dissertation has led to four journal papers (three accepted, one submitted) and five conference papers.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This Ph.D. Dissertation focuses on the proposal of a novel converter topology applied to the connection of an energy storage system, composed of a supercapacitor bank and a battery bank, to the dc bus of a residential microgrid. The proposed full-bridge-forward integrated dc-dc converter presents high voltage gain between the input and output, a fundamental requirement for the desired application, bidirectional power flow, galvanic isolation, among other features. The integration process, operation stages (including converter waveforms and equations), design methodology, dc modeling, among others, are presented. Three different clamping circuits structures are studied and applied to the proposed converter. Moreover, a comparison including several parameters with the dual active bridge converter, which is one of the most used topologies for similar applications is performed, highlighting the lesser number of active switches. Experimental results of the proposed converter in different operation modes are presented, validating the theoretical analysis. Experimental results of the dual active bridge converter are also presented and its performance is compared to the proposed converter, where it can be seen that the efficiency of the proposed converter is higher. The topology application is directed to microgrid systems, which attract high attention nowadays due to the possibility of renewable electric energy generation through distributed energy resources and with high reliability. / Esta Tese de Doutorado tem como foco a proposta de uma nova topologia de conversor aplicado para conexão de um sistema de armazenamento de energia, composto de um banco de supercapacitores e um banco de baterias, ao barramento CC de uma microrrede residencial. O conversor CC-CC integrado full-bridge-forward proposto apresenta alto ganho de tensão entre a entrada e saída, requisito fundamental para a aplicação desejada, fluxo de potência bidirecional, isolação galvânica, entre outras características. O processo de integração, etapas de operação (incluindo formas de onda e equações do conversor), metodologia de projeto, modelagem CC, entre outros, são apresentados. Três diferentes estruturas de circuitos grampeadores são estudadas e aplicadas ao conversor proposto. Além disso, uma comparação de diversos parâmetros com o conversor dual active bridge, que é uma das topologias mais utilizadas para aplicações semelhantes é realizada, destacando o menor número de interruptores. Resultados experimentais do conversor proposto em diferentes modos de operação são apresentados, validando as análises teóricas. Resultados experimentais do conversor dual active bridge também são apresentados e o seu desempenho é comparado ao do conversor proposto, onde se observa que o rendimento do conversor proposto é superior. A aplicação da topologia é voltada para sistemas de microrrede, os quais atraem grande atenção atualmente devido à possibilidade de geração de energia elétrica de maneira renovável através de fontes distribuídas e com elevada confiabilidade.

Battery storage devices have been widely utilized for different applications. However, for high power applications, battery storage systems come with several challenges, such as the thermal issue, low power density, low life span and high cost. Compared with batteries, supercapacitors have a lower energy density but their power density is very high, and they offer higher cyclic life and efficiency even during fast charge and discharge processes. In this dissertation, new techniques for the control and energy management of the hybrid battery-supercapacitor storage system are developed to improve the performance of the system in terms of efficiency, power quality and reliability. To evaluate the findings of this dissertation, a laboratory-scale DC microgrid system is designed and implemented. The developed microgrid utilizes a hybrid lead-acid battery and supercapacitor energy storage system and is loaded under various grid conditions. The developed microgrid has also real-time monitoring, control and energy management capabilities. A new control scheme and real-time energy management algorithm for an actively controlled hybrid DC microgrid is developed to reduce the adverse impacts of pulsed power loads. The developed control scheme is an adaptive current-voltage controller that is based on the moving average measurement technique and an adaptive proportional compensator. Unlike conventional energy control methods, the developed controller has the advantages of controlling both current and voltage of the system. This development is experimentally tested and verified. The results show significant improvements achieved in terms of enhancing the system efficiency, reducing the AC grid voltage drop and mitigating frequency fluctuation. Moreover, a novel event-based protection scheme for a multi-terminal DC power system has been developed and evaluated. In this technique, fault identification and classifications are performed based on the current derivative method and employing an artificial inductive line impedance. The developed scheme does not require high speed communication and synchronization and it transfers much less data when compared with the traditional method such as the differential protection approach. Moreover, this scheme utilizes less measurement equipment since only the DC bus data is required.

La production intermittente et aléatoire des énergies renouvelables, sources photovoltaïques et éoliennes, est toujours un problème pour leur intégration massive dans le réseau public. L'une des solutions est de grouper des sources renouvelables, des sources traditionnelles, des dispositifs de stockage et des charges locales, et les traiter comme une seule unité dans le réseau public. Il s'agit du concept "micro-réseau". Un micro-réseau a des potentiels pour mieux répondre aux besoins de l'utilisateur final et du réseau public, et il facilite la mise en œuvre de futur smart grid, soit le réseau intelligent.Basé sur un micro-réseau représentatif en zone urbaine et intégré aux bâtiments, cette thèse propose une supervision multicouche, afin d'effectuer une étude systémique en mettant en exergue un verrou scientifique concernant l'implémentation d'une optimisation dans l'exploitation en temps réel.La supervision traite un ensemble d’opérations telles que : l'équilibré des puissances,l'optimisation des coûts énergétiques, utilisation de métadonnées, et échange d'informations avec le réseau intelligent et avec l'utilisateur final. Cette supervision a été validée par des tests expérimentaux. Malgré les incertitudes concernant les prévisions météorologiques, la faisabilité d'implémentation de l'optimisation dans l'exploitation réelle est vérifiée. La supervision proposée est en mesure de gérer efficacement les flux en assurant l'équilibre des puissances dans tous les cas. Néanmoins, la performance d'optimisation est liée aux précisions de prédiction. Ce problème peut être amélioré dans les travaux futurs par la mise à jour des résultats d'optimisation en temps réel. / The intermittent and random production of renewable sources, such as photovoltaic and wind turbine, is always a problem for their large-scale integration in the utility grid. One of the solutions is to group renewable sources, traditional sources, storage and local consumption and treat it as a single unit in the utility grid. This is the concept of microgrid. A microgrid has the potentials of better responding both grid and end-user requirement, it facilitate the implementation of future smart grid. Based on a representative microgrid in urban area and integrated in buildings, this thesis proposes a multi-layer supervision, in order to realise a systemic study while particularly attempting to cover the research gap of implementing optimisation in realtimeoperation. The supervision handles together power balancing, energetic cost optimisation, metadata using, and information exchanges from both end-users and the smart grid. The supervision has been validated by experimental tests. The feasibility of implementing optimisation in real-time operation is validated even with uncertainties. The supervision is able to manage efficiently the power flow while maintaining power balancing in any case. Nevertheless, optimization effect relies on prediction precision. This problem can be improved in future works by updating optimization in real-time.

The main focus in this thesis is to evaluate if the microgrids is an option to be utilized for the future in achieving 100% renewable power with a net zero carbon emissions. This is an ongoing goal from the ambitious Swedish energy policy with the main points that was established in the Paris Agreement that is a legally binding international treaty on climate change.Sweden is currently in a good position due to the country’s power system is borderline decarbonized. This is due to the use of the hydropower resources and nuclear power in addition to district heating fueled by biomass. The majority of the electrical production today will need the assistance thus the need for solutions to reach the end goal because majority of the non-environment friendly energy production is being phased out such as nuclear power plants. With this in mind this study will give an overview if microgrids can be utilized, be favorable in an economical sense and to be viewed as its own entity due to its management and control options.

The main focus in this thesis is to evaluate if the microgrids is an option to be utilized for the future in achieving 100% renewable power with a net zero carbon emissions. This is an ongoing goal from the ambitious Swedish energy policy with the main points that was established in the Paris Agreement that is a legally binding international treaty on climate change.Sweden is currently in a good position due to the country’s power system is borderline decarbonized. This is due to the use of the hydropower resources and nuclear power in addition to district heating fueled by biomass. The majority of the electrical production today will need the assistance thus the need for solutions to reach the end goal because majority of the non-environment friendly energy production is being phased out such as nuclear power plants. With this in mind this study will give an overview if microgrids can be utilized, be favorable in an economical sense and to be viewed as its own entity due to its management and control options.

The energy demand is increasing very rapidly all over the world. Solar energy is one renewable solution to cover the energy demand. Solar power is a universal green energy source, and we receive from the sun more than ten thousand times energy than it has needed on the earth. This report investigates the electricity generation by using solar PV panels for the given village as well as the transmission systems. The main priority of this report is to calculate the demand electricity of the village, plant design also considering the power losses. Three different scenarios to transmit the generated power to the consumers end were considered and studied. The three different cases and cases are, • Grid connection. • Micro-grid power supply system with full battery storage. • Micro-grid power supply system with partial battery storage. All three system were analyzed based on the technical specifications, power losses during transmission. The all calculation was completed by the help of different software, such as PVGIS, MS excel, different empirical formulas and previous research papers. To complete the calculation this, report also consider a few assumptions. After completing all analysis and calculations, the research outcome was showing that the microgrid power supply system with whole battery backup storage will be the better solution both technically and economically. Photovoltaic (PV) solar cell-based microgrid systems can be one of the most feasible solutions to provide electricity in rural areas. Therefore, this system can play a vital role in Bangladesh to provide electricity in rural areas. In Bangladesh, there are several positive aspects to promote the use of photovoltaics (PV), such as many solar irradiations, low technology and labour cost, and a few subsidies from the government.

abstract: This dissertation covers three primary topics and relates them in context. High frequency transformer design, microgrid modeling and control, and converter design as it pertains to the other topics are each investigated, establishing a summary of the state-of-the-art at the intersection of the three as a baseline. The culminating work produced by the confluence of these topics is a novel modular solid-state transformer (SST) design, featuring an array of dual active bridge (DAB) converters, each of which contains an optimized high-frequency transformer, and an array of grid-forming inverters (GFI) suitable for centralized control in a microgrid environment. While no hardware was produced for this design, detailed modeling and simulation has been completed, and results are contextualized by rigorous analysis and comparison with results from published literature. The main contributions to each topic are best presented by topic area. For transformers, contributions include collation and presentation of the best-known methods of minimum loss high-frequency transformer design and analysis, descriptions of the implementation of these methods into a unified design script as well as access to an example of such a script, and the derivation and presentation of novel tools for analysis of multi-winding and multi-frequency transformers. For microgrid modeling and control, contributions include the modeling and simulation validation of the GFI and SST designs via state space modeling in a multi-scale simulation framework, as well as demonstration of stable and effective participation of these models in a centralized control scheme under phase imbalance. For converters, the SST design, analysis, and simulation are the primary contributions, though several novel derivations and analysis tools are also presented for the asymmetric half bridge and DAB. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2019

abstract: This work introduces self-organizing techniques to reduce the complexity and burden of coordinating distributed energy resources (DERs) and microgrids that are rapidly increasing in scale globally. Technical and financial evaluations completed for power customers and for utilities identify how disruptions are occurring in conventional energy business models. Analyses completed for Chicago, Seattle, and Phoenix demonstrate site-specific and generalizable findings. Results indicate that net metering had a significant effect on the optimal amount of solar photovoltaics (PV) for households to install and how utilities could recover lost revenue through increasing energy rates or monthly fees. System-wide ramp rate requirements also increased as solar PV penetration increased. These issues are resolved using a generalizable, scalable transactive energy framework for microgrids to enable coordination and automation of DERs and microgrids to ensure cost effective use of energy for all stakeholders. This technique is demonstrated on a 3-node and 9-node network of microgrid nodes with various amounts of load, solar, and storage. Results found that enabling trading could achieve cost savings for all individual nodes and for the network up to 5.4%. Trading behaviors are expressed using an exponential valuation curve that quantifies the reputation of trading partners using historical interactions between nodes for compatibility, familiarity, and acceptance of trades. The same 9-node network configuration is used with varying levels of connectivity, resulting in up to 71% cost savings for individual nodes and up to 13% cost savings for the network as a whole. The effect of a trading fee is also explored to understand how electricity utilities may gain revenue from electricity traded directly between customers. If a utility imposed a trading fee to recoup lost revenue then trading is financially infeasible for agents, but could be feasible if only trying to recoup cost of distribution charges. These scientific findings conclude with a brief discussion of physical deployment opportunities. / Dissertation/Thesis / Doctoral Dissertation Systems Engineering 2019