Simulation, Control and Analysis of a 3-phase 3-level NPC Converter in Grid-Connected Systems

Sammanfattning

The integration of renewable energy sources into modern power grids necessitates the use of power electronic converters capable of handling high voltages. Multilevel converters offer advantages compared to traditional 2-level converters by provid- ing multiple voltage levels, improved efficiency, and better power quality. However, maintaining balanced DC link voltages presents additional complexity in control algorithms. This thesis aims to implement a functional grid-connected 3-level NPC (Neutral Point Clamped) converter. Initially, simpler designs such as a buck converter, an H-bridge converter, and a 2-level converter were investigated and simulated. This ensured a structured ap- proach as each design introduced relevant challenges and concepts necessary for the implementation of the 3-level converter. After simulation, the core focus was on code implementation using a microcontroller where the 2-level converter was first imple- mented, followed by the 3-level converter. Experimental setups involved connecting the 2-level and 3-level converters to the grid and controlling the output currents. The power quality of the converters was evaluated and compared to each other and the corresponding simulations. In conclusion, the power quality of the 3-level con- verter surpasses that of the 2-level converter. Discrepancies in power quality between simulations and experimental results suggest potential factors such as transformer- induced voltage distortions or electromagnetic interference in the setup. Further research could focus on integrating DC-voltage control and running the converter as an active dynamic filter.