Hierarchical energy management system design and implementation for microgrids

Microgrids provide a solution for the direct consumption, storage and distribution of local energy sources by allowing renewable energy sources to be integrated into power systems. In this thesis study, an energy management system with a hierarchical three-level control approach is proposed, and simulation studies are carried out for an islanded DC microgrid system with photovoltaic, wind turbine, diesel generator, and energy storage. In the hierarchical three-level control, the primary control layer ensures the control of the converter. The secondary control layer is used to restore DC bus voltage and increase current-sharing accuracy simultaneously. In the tertiary control layer, it is aimed to minimize the production cost by performing optimum load-sharing. For the operation of this control structure, a strategy is proposed to autonomously and optimally manage the energy demand of the hybrid system under variable load conditions. Three operating methods, namely Mode-I, Mode-II, and Mode-III, are defined in the energy management system. In Mode-I, maximum power point tracking of renewable resources is provided. In Mode-II, energy consumption minimization strategy-based linear programming, genetic algorithm and pattern search algorithms are used to minimize the diesel generator's fuel consumption and carbon emissions. In Mode-III, the diesel generator is not needed, and the power flow between the distributed resources is optimized using the fuzzy logic controller and state machine control strategy. Power converters play a significant role in managing renewable energy sources in microgrid applications. In this regard, a power factor corrected and highly efficient boost-type converter design and implementation have been carried out. The designed DC-DC converter has been utilized and tested in experimental studies. A DC microgrid structure consisting of three identical distributed energy sources, load, and control blocks has been created for the experimental test setup. Two-level hierarchical energy management approach has been employed for power-sharing among distributed energy sources. In experimental studies, conventional droop control, adaptive droop control, power sharing according to different current sharing ratios, the system's response to the change of reference voltage and the plug-and-play performance of the system are systematically discussed and evaluated. The results showed that the proposed adaptive droop control improved DC bus voltage restoration and current-sharing accuracy.