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- Goncalves de Oliveira, Janaína
(författare)
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Power Control Systems for PM Synchronous Flywheel Alternators
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Flywheel systems are attractive in hybrid and electric vehicles, being able to handle the large power when accelerating and for regenerative braking. The combination of a flywheel device with a battery source has several advantages, such as higher peak power capacity, higher energy density and a decrease of the number of charging/discharging cycles in the battery. The Flywheel Energy Storage System here investigated has its novelty in the use of a double wound flywheel motor/generator to divide the system in two different voltage/power levels. High-Voltage (HV) side connects the flywheel machine to the wheel motor and Low-Voltage (LV) side connects the flywheel machine to the battery. This thesis deals with the power control systems involved in the connection between different components of the system. Bidirectional DC/DC and DC/AC converters are used to connect the flywheel motor/generator to the battery in the LV side. The DC/AC converter design and construction is the main focus of the present licentiate thesis. Two different scaled prototypes have been tested. A speed motor drive was designed and tested with the first scaled prototype, in which different filter and motor load connections were investigated. Results have shown that low harmonic distortion can be obtained in the inverter output voltage and current. The second scaled prototype is a Two Voltage Levels Machine. The bidirectional DC/AC converter has been designed so the LV side of the system could work in a fast and efficient way. Simulations have shown the dynamics of the system, which has also been tested experimentally under a drive cycle. The flywheel has shown to be able of delivering smooth power to the battery side, despite the variations in the load side. A scaling factor has been applied in order to extrapolate the results to a full-scaled system. Investigations have also been made about the battery recharging process. The main challenge is the control of the power flow despite the voltage variations of the flywheel machine as dependent on its charge state, i.e. rotational speed. A DC/DC buck/boost converter under PI control has been designed and simulated, being able to keep either the current or the voltage constant on the battery side when the machine speed is decreasing.
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| 2. |
- Santos Döhler, Jéssica
(författare)
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Microgrid Power Control Strategies: Enabling Distributed Energy Resources in Power Systems
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As the world continues to deal with the effects of climate change, the need for carbon neu-trality becomes increasingly urgent. To achieve this goal, many countries are exploring the potential of distributed energy resources to reduce their dependence on fossil fuels and transition to renewable sources of energy. A microgrid is a small, independent energy system that can operate on its own or in connection with the main power grid. It integrates different energy sources like solar panels and batteries. Inverters are crucial in microgrids as they facilitate the seamless integration of various energy sources and contribute to grid stability. These inverters can be categorized into three distinct groups: grid-feeding, grid-supporting, and grid-forming. Each category serves a unique purpose, from synchronizing power with the main grid to providing support during grid disturbances and even enabling autonomous grid operation. These varying inverter functionalities contribute to the adaptability and resilience of microgrids, ensuring they can meet diverse energy needs and operate effectively in a range of scenarios. The thesis provides a comprehensive background of critical aspects of power systems and distributed energy resources, specifically focusing on microgrids and their significance in the evolving energy landscape. A particular emphasis is placed on the crucial functions served by inverters within microgrid architectures. Additionally, the thesis delves into fault analysis and mitigation strategies to ensure system resilience. Furthermore, the study highlights the importance of hybrid energy storage systems in enhancing the power quality of wave energy converters, achieved through the mitigation of power fluctuations. The outcomes and results of this thesis were developed and simulated using two platforms: MATLAB/Simulink and PSCAD. It delves into five distinct scenarios, each examining microgrid inverters from different perspectives in terms of circuit topology and control structures. The first one, shows the integration of a hybrid energy storage system as a key factor in elevating system efficiency, mitigating power fluctuations, and optimizing battery performance within the context of a wave energy system. In the second scenario, the thesis shifts its attention to grid-feeding and grid-forming inverters connected to a three-phase four-wire power system. The results showed the effectiveness of the suggested control strategy with smooth synchronization where the grid-forming inverter was able to form a network with an unbalanced factor lower than 2%, sinusoidal voltage, and frequency within standard limits. The third scenario places its emphasis on grid-supporting inverter, showcasing adaptability, and robust response to fault conditions by injecting or absorbing power, helping to mitigate voltage dips and fluctuations. The fourth, grid-forming inverter successfully formed a network with an unbalanced degree lower than standard regulations, maintaining sinusoidal voltage and frequency within standard limits. The fifth scenario explores the potential benefits and challenges of combining grid-feeding, grid-supporting, and grid-forming inverters as multi-functional inverters in the context of grid integration of wave energy converters. The multifunctional inverter configuration offers increased operational flexibility and resilience, effectively addressing a wider range of grid and microgrid possibilities.
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