Pedro Leal dos Santos

• Driven by rising global energy demand and the urgent need to reduce carbon emissions, large-scale electrification has become a critical objective – particularly through the integration of renewable energy sources and energy storage systems. These technologies are inherently Direct Current (DC) in nature, challenging the long-standing dominance of Alternating Current (AC) infrastructure and naturally promoting a structural change towards DC and hybrid AC/DC power systems. This transformation is made feasible by advancements in power electronics, where multilevel converter topologies such as the Modular Multilevel Converter (MMC) may play a key enabling role due to their scalability, efficiency, and operational flexibility. This thesis explores two innovative capabilities of the MMC that enhance its functionality as an interconnecting element between distinct power networks. The first contribution introduces the concept of power decoupling between AC and DC grids. By leveraging the MMC’s flexible energy storage, the system enables independently shaped transient responses on both grid sides–offering a valuable opportunity to strengthen the interface between weak or mismatched networks. A hierarchical control structure is developed, combining Input-Output Feedback Linearization (IOFL) based controller, an extended disturbance observer, and a 2-Degree-of-Freedom (DOF) outer loop controller, validated through hardware implementation on a laboratory MMC prototype. A long-horizon Model Predictive Controller (MPC) is also introduced to handle system constraints, with its real-time feasibility evaluated in a Processorin-the-Loop (PiL) environment. The second contribution presents a high stepdown MMC-based DC to DC Converter (DC-DC) converter designed specifically for heavy-duty agricultural electrification, a sector traditionally difficult to electrify. In this application, a Medium-Voltage Direct Current (MVDC) microgrid supplies power to mobile agricultural machines. The converter uses an unconventional configuration of permanently inserted submodules to achieve transformerless operation and increased power density. A 300 kW hardware demonstrator is designed to experimentally validate the converter operation. A reduced-order model is developed to support the design of an adaptive controller, capable of maintaining a stable and uniformly responsive behavior under rapidly changing load conditions. In summary, this work demonstrates how the MMC – when paired with advanced control strategies can be a critical component of for future grid architectures and enable electrification in challenging applications. The proposed approaches contribute to the development of robust, flexible, and scalable power conversion systems essential for realizing the next generation of energy infrastructure.