Advanced Control Strategies for Multilevel Power Converters in Hybrid Microgrid Applications
- Publication Type:
- Thesis
- Issue Date:
- 2019
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In recent years, the traditional electrical power grids are gradually changing into smart grids and emerging as the next-generation power systems. The application of power electronics is playing a vital role in these changes. The recent advancements in power electronics have provided significant momentum for high penetration of renewable energy sources, energy storages, and modern loads into the hybrid microgrid associated with the smart grid. Nevertheless, it also introduces several challenges in terms of reliability and robustness, power quality, and cost. Developing advanced control strategies and converter architecture to mitigate these challenges will be vital. This thesis presents advanced control strategies and circuit architectures for the grid-connected system in hybrid-microgrid applications. The system parameter variations and uncertain disturbances are critical for achieving the control objectives in AC/DC power conversion. In this thesis, disturbance rejection based control strategies have been proposed and implemented to ensure improved steady-state and dynamic performances to follow the references. The control of power converters connected with the electrical grid requires fast and accurate estimation of grid voltage parameters (i.e., amplitude, phase, and frequency), which are carried out using the grid synchronization method. The performance of synchronization methods is affected by the growing power quality issues. This thesis presents novel methods for fast and accurate estimation of the grid voltage parameters. These methods demonstrate enhanced performance to eliminate the disturbances, such as the presence of DC-offset, harmonically distorted grid, grid frequency variations, voltage sag and swell, etc. This thesis also presents a novel single-source three-phase multilevel converter with voltage boosting capability for medium-voltage photovoltaic applications. The new circuit structure significantly reduces the DC-link voltage requirements, the number of components and their voltage stresses in comparison to traditional topologies. It can reduce the dc-link voltage requirements by 75% in comparison to the traditional neutral point clamped (NPC), flying capacitors, active NPC (ANPC), hybrid and hybrid clamped ANPC topologies, and 50% to advanced ANPC topologies. It can also reduce the number of required switches and capacitors as well as their voltage stresses compared to these state-of-the-art topologies reported in the literature so far. The performance of the proposed control techniques and circuit topologies have been validated by simulation and experimental results.
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