Microgrid Power Control Strategies: Enabling Distributed Energy Resources in Power Systems

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.