PLANNING STUDIES FOR AC MICROGRIDS

Abstract

In recent years, there has been a growing interest in the planning and implementation of AC microgrid systems due to their potential to enhance the reliability, efficiency, and sustainability of electrical power distribution systems. AC microgrids are small-scale power systems operating independently or in parallel with the primary grid, integrating various distributed energy resources (DERs) such as renewable energy sources (RESs), energy storage systems (ESS), and controllable loads. However, intermittent RESs introduce challenges in operation due to dynamic and erratic variations in power generation. Moreover, load dynamics is an additional variable which can significantly impact the overall stability and performance of the AC microgrid system. Therefore, in microgrid systems, renewable energies are integrated with conventional DERs and ESS to handle this power generation and load dynamics intermittency. The operation control technique of both conventional and non-conventional distributed generators (DGs) is crucial, as it manages the power flow from these DGs. Generally, renewable energy is operated at their maximum power point to extract the maximum possible power. In contrast, conventional DGs are utilised optimally to bridge the gap between RESs and load demands while supporting voltage and frequency. Therefore, it becomes essential to consider their respective power regulation strategies in the planning stage to achieve the best optimum, economical and steady-state operation-efficient microgrid structure. Load flow is an essential step while planning and investigating the microgrid system. Traditional load flow techniques such as Newton Raphson and Gauss-Seidel methods often lead to divergence when applied in distribution systems due to different characteristics from the transmission system. Therefore, load flow techniques such as backwards-forward sweep methods are used to assess the power flow in the system; however, being iterative, the process is computationally complex, and its complexity increases with the system’s size. Following the planning stage, the next phase involves operating and managing the system’s performance. However, intermittency associated with RESs is challenging in maintaining steady and stable system performance parameters within the permissible limits. This thesis addresses the challenges in microgrid planning and performance investigation by introducing the planning strategies that consider the appropriate power regulation scheme based on respective conventional and non-conventional DGs. The work proposes alternative techniques for power flow analysis by utilizing regression techniques and artificial neural networks for assessing the steady-state performance concerning voltage and line losses in the distribution system. Moreover, studies on series capacitor placement have been addressed to improve the system’s voltage profile and power efficiency. The transient conditions arising from source and load side dynamics have been addressed, and the influence of energy storage schemes (battery storage and hybrid energy storage systems) has been discussed. Additionally, a discussion on the control strategy applied to battery storage with rate limiter has been presented in detail, discussing its impact on battery operation and efficiency. Overall, this thesis contributes to the field of power system engineering, offering innovative solutions to enhance the planning, operation, and performance of distribution systems. The proposed techniques and methodologies provide valuable tools for system planners and operators to optimize system performance, improve reliability, and facilitate the integration of renewable energy sources and energy storage systems.