Modeling, Design and Analysis of a Multiport Conversion System for Future Electric Vehicles Charging Infrastructures

This dissertation presents the research activities carried out in the framework of advanced charging systems for electrified transportation, with the overarching goal of improving the efficiency, power density, and scalability of future medium-voltage DC (MVDC) charging infrastructures. The rapid growth of electric vehicles (EVs), together with the increasing deployment of renewable energy sources and DC-based systems, is driving the development of power conversion architectures capable of satisfying stringent requirements in terms of galvanic isolation, bidirectional power flow, modularity, and compatibility with heterogeneous energy storage technologies. Achieving these objectives, however, requires the simultaneous advancement of several tightly interconnected technologies. Batteries are dynamic loads, as their voltage changes during charging and discharging, requiring power converters to adapt their output to the load requirements. For this reason, battery models are essential for accurately representing the electrical behavior of the battery energy storage systems (BESSs) and supporting converter design and control strategies. In turn, converters must be capable of meeting the load requirements in terms of voltage and current, according to the operating strategy. Consequently, their operating point is not fixed but depends on the load, which may vary considerably, particularly because EV fleets and stationary BESSs employ different battery chemistries. Their performance therefore cannot be optimized for a single scenario; instead, they must perform well across a broad range of operating conditions. Moreover, the converter architecture defines the electrical specifications and operating conditions of the magnetic components, whose characteristics strongly influence the efficiency, power density, thermal performance, and insulation capability of the overall system. Improvements in these subsystems therefore cannot be considered independently, as design choices in one directly affect the performance of the entire charging infrastructure. Within this framework, the research activities presented in this dissertation address three complementary aspects of the same engineering problem: the development of advanced methodologies for battery modeling and characterization, the design and optimization of medium-voltage medium-frequency (MV-MF) planar transformers (PTs), and the analysis of an innovative isolated multiport DC-DC converter for future EV charging applications. While each research activity focuses on a specific subsystem, all of them contribute toward the common objective of enabling more efficient, compact, reliable, and scalable charging infrastructures for next-generation DC energy systems.