Energy management of multilevel converters in microgrid

• Main Author: Shreyas, Dethe
• Other Authors: Amer M. Y. M. Ghias
• Format: Thesis-Master by Coursework
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Electrical and electronic engineering::Power electronics
• Online Access: https://hdl.handle.net/10356/163204
• Institution: Nanyang Technological University

Microgrids are emerging as a new way to implement and test new power generation and distribution technologies, and slowly penetrate them into the main grid. Their small size provides advantages such as better control, distribution and security. Microgrids are being implemented around the world for the increased use of renewable energy sources, that is brought by the growing demand for cleaner and sustainable such energy sources in the modern industrial world. Some offshore areas use microgrids in the islanded mode disconnected from the main grid, and rely on solar and wind power for their energy demands. Recently, even smaller grids called nanogrids are being implemented, with their scale being as small as that of a single building. With the demand for environmentally cleaner energy, the demand for reliable and cleaner power increases too. The small size of the microgrid brings challenges forward such as reliability since a majority of renewable power is intermittent in nature, increased harmonic content due to the extensive use of semiconductor power converters, weak grid etc. Energy storage systems such as batteries and ultracapacitors are slowly being included in the industry, however the sustainability of chemical batteries is questionable. Various converter topologies are being explored with the goal of reducing the generation of harmonic content as much as possible, while efficiently utilizing the nature of renewable power. In this work, a multilevel converter topology named Cascaded H-Bridge is implemented as a grid-connected power converter for PV and BESS systems and its performance is analyzed under various stress conditions. Software simulations are performed to assess the models, the control systems and the energy management algorithm. In the first experiment, the total solar power output was reduced by means of partial shading on the PV arrays. The converter was able to adjust the power flow to the grid by taking power from the batteries and discharging them. In the second experiment, the grid side power demand was varied in short intervals, similar to some real-world load profile. The controller was observed to respond to the changes in the load by diverting power to or from the BESS according to the power balance between the solar power generation and the grid side load.