The proliferation of distributed energy resources (DER)s has prompted interest in the expansion of DC power systems. The technological limitations that hinder the expansion of DC power systems are the absence of DC circuit breakers and high step-up/high step-down DC converters for interconnecting DC systems. This thesis presents a transformerless high step-up DC-DC converter intended for use as an interconnect between DC systems. The converter is required to operate at medium to high voltage (>1kV) and provide high voltage gain (>5). This work details the steady state operation and dynamic model of the proposed converter. The component ratings are identified and converter design limitations are investigated. A 100V:1kV/4kW prototype is produced to verify the analytic steady state model and measure efficiency. An experimental efficiency of 90% was achieved at a step-up ratio of 1:10, however efficiency at low power is limited due to the need to circulate power.

The proliferation of distributed energy resources (DER)s has prompted interest in the expansion of DC power systems. The technological limitations that hinder the expansion of DC power systems are the absence of DC circuit breakers and high step-up/high step-down DC converters for interconnecting DC systems. This thesis presents a transformerless high step-up DC-DC converter intended for use as an interconnect between DC systems. The converter is required to operate at medium to high voltage (>1kV) and provide high voltage gain (>5). This work details the steady state operation and dynamic model of the proposed converter. The component ratings are identified and converter design limitations are investigated. A 100V:1kV/4kW prototype is produced to verify the analytic steady state model and measure efficiency. An experimental efficiency of 90% was achieved at a step-up ratio of 1:10, however efficiency at low power is limited due to the need to circulate power.

Urban microgrids are smart and complex energy systems that help integrate renewables into our cities, turning our neighborhoods into partly energy self-sufficient hubs. Moreover, they create the space for electricity transactions between neighbors, transforming the former consumers into prosumers. The following work proposes the implementation of an urban microgrid to a neighborhood in Lisbon, Portugal. This dissertation’s objective is designing and discovering the optimal photovoltaic and storage capacity, optimal electricity dispatch, effects of distributed energy production in grid voltage and economic viability of such a system. With this purpose, a comprehensive model was elaborated, considering specific site weather data, electric loads, grid topology and utility tariffs. The self-sufficiency of Arco do Cego was found to be 66% in this study, reducing its carbon footprint by 61%. A detailed map of where to place each PV system and battery bank was generated, with specific electricity dispatch strategies. Moreover, the system was designed under real grid voltage, current and power flow constraints.

abstract: The Internet and climate change are two forces that are poised to both cause and enable changes in how we provide our energy infrastructure. The Internet has catalyzed enormous changes across many sectors by shifting the feedback and organizational structure of systems towards more decentralized users. Today’s energy systems require colossal shifts toward a more sustainable future. However, energy systems face enormous socio-technical lock-in and, thus far, have been largely unaffected by these destabilizing forces. More distributed information offers not only the ability to craft new markets, but to accelerate learning processes that respond to emerging user or prosumer centered design needs. This may include values and needs such as local reliability, transparency and accountability, integration into the built environment, and reduction of local pollution challenges. The same institutions (rules, norms and strategies) that dominated with the hierarchical infrastructure system of the twentieth century are unlikely to be good fit if a more distributed infrastructure increases in dominance. As information is produced at more distributed points, it is more difficult to coordinate and manage as an interconnected system. This research examines several aspects of these, historically dominant, infrastructure provisioning strategies to understand the implications of managing more distributed information. The first chapter experimentally examines information search and sharing strategies under different information protection rules. The second and third chapters focus on strategies to model and compare distributed energy production effects on shared electricity grid infrastructure. Finally, the fourth chapter dives into the literature of co-production, and explores connections between concepts in co-production and modularity (an engineering approach to information encapsulation) using the distributed energy resource regulations for San Diego, CA. Each of these sections highlights different aspects of how information rules offer a design space to enable a more adaptive, innovative and sustainable energy system that can more easily react to the shocks of the twenty-first century. / Dissertation/Thesis / Doctoral Dissertation Sustainability 2018

Microgrid is an emerging technology in the eld of electrical engineering which employs the concept of Distributed Energy Resources (DERs) in order to generate electricity in a small sized power system. The main objectives of this dissertation are to: 1- design a new control for lower level control of DERs in microgrids, 2- implement distributed upper level control for DERs in microgrids and 3- apply analytical approaches in order to analyze DERs in microgrids. The control in each DER can be divided into two main categories: lower and upper level. Lower level control is the main objective of control in each DER. For example, the lower level control in Photovoltaic (PV) is in charge of transferring the maximum power from sun into the main grid. Unlike the lower level control, the upper level control is an additional control loop on top of the lower level controls. For example, Voltage/Frequency (VF) controllers are installed on top of Active/Reactive (PQ) power controller in energy storage devices as upper level control. In this dissertation, for the lower level control improvements, two widely used DERs are selected (PV, and oshore wind farm) and new control algorithms are developed in order to improve the performance of lower level controllers in these DERs. For the PV lower level improvement, a new control methodology is proposed in order to minimize the maximum power tracking error in PV lower level controller. Second contribution in lower level control is for the oshore wind farm applications based on Multi-Terminal High Voltage Direct Current (MTDC) transmission; a new control is designed in order to minimize the losses in transmission lines through lower level control of High Voltage Direct Current (HVDC) converters. For the upper level control, this dissertation considers the energy storage as another mostly used type of DER in microgrids. The lower level control for energy storage is in charge of controlling the PQ of the energy storage. The main contribution in the upper level control is to implement the distributed control algorithm based on consensus theory for battery energy storages in order to maximize the efficiency, energy management as well as synchronizing the performance of parallel energy storage devices in microgrids. In this case, the consensus based distributed control algorithm with limited information exchange between neighboring energy storage units is proposed and implemented to validate the claim. The third contribution of this research is to apply advanced analysis techniques to evaluate the performance of the DERs in microgrids. Two approaches are introduced for microgrid modeling in this research. Firstly, an impedance modeling technique is used to model the oshore wind farm connected to the main AC grid through HVDC transmission line. Multiple Input Multiple Output (MIMO) Nyquist analysis and singular value analysis are used to assess the interactions between HVDC converter and grid. Secondly, an unbalanced microgrid is considered and Dynamic Phasor (DP) analysis is applied in order to nd the stability limitations under different scenarios. This dissertation has led to seven journal papers (five published, one journal in revision process and one journal submitted recently) and four conference papers.

Over recent years, political, technological, environmental and economic factors have combined to increase interest in distributed energy resources (DER), and flexibility in the power system. As a resource which is both distributed and flexible, flexible demand (FD) can be considered to be particularly of interest. However, due to many facets of its nature, understanding the available flexibility, and potential value of that flexibility, is difficult. Further, understanding the effects of FD exploitation on other multi-energy system actors, given the complex nature of modern liberalised energy systems, complicates the picture further. These factors form material obstructions to the assessment of FD, for example, for the construction of business cases. To address these gaps this thesis first assesses the nature and value of various applicable current and potential markets and charging/incentive regimes, before detailing a novel multi-energy domestic demand simulation model, capable of modelling, in detail, domestic FD resources. Subsequently, a multi-commodity stochastic energy/reserve optimisation model, capable of modelling various DERs and taking into account price signals related to various energy-related commodities and services (including user utility) is specified. The separation of price components for application at different aggregation levels, which is applied in the optimisation model, also informs the described value mapping methodology, which illustrates the impacts of any, particularly demand-side, intervention on the wider multi-energy system. The power of the above detailed contributions are demonstrated through various studies, which show the physical and economic impact of various demand side interventions and of greater market participation by FD resources.

Les évolutions récentes des systèmes électriques comme conséquence de la dérégulation du marché et des traités internationaux comme le protocole de Kyoto ont des répercussions importantes sur les réseaux, en particulier, ceux de distribution. En effet, une large part de la production décentralisée est prévue d'être raccordée sur ces derniers. La production décentralisée utilise des sources d'énergie renouvelables hautement imprévisibles et reparties dans la nature. Ce fait ajoute une contrainte forte sur la planification et l'exploitation des réseaux de distribution qui n'ont pas été conçus, à l'origine, pour accueillir de la production d'énergie à large échelle. Ce travail de thèse étudie l'impact de l'incertitude sur les études classiques de planification des réseaux électriques. Les études statiques et dynamiques du réseau ont été réalisées prenant en compte plusieurs sources d'incertitude dans plusieurs réseaux de distribution. Les incertitudes sont modélisées dans les études statiques par les méthodes probabilistes et possibilistes. La méthode possibilistes offre des avantages sur la méthode probabiliste. Il est déterminé le taux de pénétration éolien maximum d'un petit réseau maillé en utilisant la méthode probabiliste, ainsi que les simulations de stabilité dynamique et statique du réseau / The recent developments in power systems, as consequence of the market deregulation and the international treaties, as the ones originated by the Kyoto Protocol, have serious repercussions in power networks. Particularly on distribution networks, given that a large amount of distributed generation units are connected in the grid. For instance, renewable energy sources, that are used as distributed generation, are well-known for being distributed in nature and highly unpredictable. This fact adds a strong constraint on planning and operating the distribution networks that were not originally designed to accommodate distributed generation on a large scale. To this aim, this thesis examines the impact of uncertainties on classical power system planning studies, where classical static and dynamic planning studies are carried out in several power networks taking into account some sources of uncertainty. These uncertainties are modeled in the static studies using a probabilistic and a possibilistic approach. The possibilistic approach offers good advantages over the probabilistic method in terms of time consumption and precision. The maximum wind power penetration is determined for a small mesh network by the probabilistic method using dynamic and static stability simulations of the power system.

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