Power electronic converters for particle accelerators and nuclear fusion applications

Driven by the demand for clean, large-scale energy generation, growing electricity needs, and global climate objectives, controlled thermonuclear fusion has become central to advanced energy system development. Simultaneously, expanding medical infrastructure, particularly for cancer treatment, and progress in fundamental research are accelerating advancements in particle accelerator technologies. These applications require power converters capable of high-current operation, bidirectional power flow, unity power factor, efficient energy recovery, and precise dynamic control. This thesis investigates two key components of such power converters: the active front-end (AFE) stage based on a neutral point clamped topology, and the back-end DC/DC stage employing interleaved H-bridges (HBs). Thesis first part examines the AFE implemented in CERN’s POPS-B power converter, focusing on its operation as a reactive power compensator under light-load conditions. A novel control strategy based on instantaneous energy balance is proposed to regulate the variable DC-bus voltage, enabling dual functionality while maintaining stable operation without over-modulation or violating DC-bus voltage drop limits. Performance is evaluated using both synchronous rotating dq-frame and stationary αβ-frame control strategies, which show comparable results, with the αβ-frame providing improved decoupling of active and reactive power. A detailed harmonic analysis of neutral point currents and DC-bus voltages is conducted and validated through simulations and experiments. The second part of thesis analyzes the interleaved HB back-end converter, comparing common DC-bus (CDC) and split DC-bus (SDC) configurations. Circulating currents in the CDC topology are modeled analytically to evaluate RMS and non-zero frequency components under ideal and non-ideal conditions of interleaving inductors. A normalization method is introduced to isolate circulating current effects, and an algorithm is proposed to select the optimal topology based on design parameters and circulating current constraints. Simulation and experimental results validate the approach. Overall, this work advances power converter design for next-generation scientific and high-energy infra-structures.