STATE ESTIMATION AND UNCERTAIN POWER FLOW OF ISLANDED AC AND HYBRID AC/DC MICROGRIDS

Abstract

The Distribution System (DS) has gained significant attention in power system studies due to the integration of innovative technologies such as distributed generations from renewable energy sources (RES), internet and communication technologies (ICT), advanced monitoring technologies (AMI, smart meters), and customer participation for demand side management. The power system studies can be broadly categorized into operational and planning studies. State Estimation (SE) and Power Flow (PF) are the most critical components in operational and planning studies. These two functions (SE and PF) are crucial as other operational and planning functions heavily rely on the results of SE and PF, such as fault detection, load balancing, and system stability analysis. The generation from renewable sources (RES) is increasing rapidly to meet the global goals of carbon neutrality, sustainable energy for the future, and eco-friendly mobility solutions. The RES integrated into DS is considered distributed generations (DGs), and they increase the efficiency of DS through reduced transmission losses. Further, the smaller size and less commissioning time reduce the capital cost of DS. The DGs increase the DS sustainability and reliability through Microgrid (MG) structures. MG is a portion of DS with a group of DGs, loads, and storage systems operating as a single control entity. Microgrids (MGs) are classified into AC, DC, and Hybrid AC/DC based on their distribution nature. These AC, DC, and hybrid AC/DC MGs can operate in two distinct modes: grid-connected and islanded. In the former, with the assumption of an infinite bus, the DGs in the DS aim to maximize the utilization of RES, and the intermittency of renewable DGs can be managed by the primary grid. However, in the face of natural calamities, grid-side faults, power quality issues, or cyber-attacks, the AC, DC, and hybrid AC/DC MGs switch to islanded mode. In this scenario, the primary objective is to find the equilibrium operating point to supply the critical loads through RES or conventional non-renewable generations. This independent operation of MGs not only enhances the reliability of the DS but also ensures the supply of power to customers even in the absence of the grid. Due to the absence of a slack bus for islanded AC, DC, and hybrid AC/DC MGs, the generation output from the DGs depends on the load requirements, with the load being shared proportionally to their maximum capacity. This approach is simple and cost-effective because it does not require any communication systems, which are prone to single-point failures. The amount of power generated by each DG in islanded AC MG (IMG) and islanded AC/DC hybrid MG (IHMG) is calculated using the droop characteristics of DGs. This thesis focuses on developing State Estimation (SE) and Uncertain Power Flow (UPF) models for Islanded AC Microgrids (IMG) and Islanded Hybrid AC/DC Microgrids (IHMG).