Design & Development of a CHB-Based Converter for Direct Integration of Renewables to the Grid

Abstract

The integration of solar photovoltaic (PV) and battery energy storage systems (BESS) into the power grid requires high-performance power electronic interfaces to replace traditional, inefficient separate converter setups. This thesis investigates a unified 10 MW/10 kV modular multilevel architecture utilizing a cascaded H-bridge (CHB) inverter integrated with dual active bridge (DAB) stages. Unlike previous models, this system uses high-frequency transformers (HFT) within the DAB stages to provide galvanic isolation and improve power density. This configuration aims to reduce power conversion stages and enhance overall system efficiency. The first phase of the research focuses on the design and implementation of the power stage and its control systems. A modular architecture is developed, and closed-loop controllers are designed to manage the bidirectional power flow between the PVBESS common DC-link and the utility grid. To evaluate the thermal behavior and efficiency of the system, the proposed model is simulated in PLECS. This allows for detailed thermal modeling to determine the relationship between the electrical dynamics and switching losses. Finally, a comprehensive comparative analysis is performed between 1.7 kV and 3.3 kV silicon carbide (SiC) MOSFETs. The study evaluates these two semiconductor technologies based on conduction and switching losses, overall system efficiency, and cost-effectiveness. The results show that while the 1.7 kV SiC model provides higher overall system efficiency, the choice of the 3.3 kV SiC model allows for a significant reduction in the cost and the total number of sub-modules while maintaining acceptable thermal performance, providing a clear design roadmap for next-generation, high-density modular systems.