Medium-Voltage Medium-Frequency Transformer for Green Hydrogen Applications
R. Mirzadarani (TU Delft - Electrical Engineering, Mathematics and Computer Science)
P.T.M. Vaessen – Promotor (TU Delft - Electrical Engineering, Mathematics and Computer Science)
P. Bauer – Promotor (TU Delft - Electrical Engineering, Mathematics and Computer Science)
M. Ghaffarian Niasar – Promotor (TU Delft - Electrical Engineering, Mathematics and Computer Science)
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Abstract
This thesis focuses on the design and development of a medium-voltage, medium-frequency solid-state transformer (SST) for large-scale green hydrogen production. The work is motivated by the need to improve the efficiency, compactness, and controllability of power conversion systems that connect renewable energy sources, such as offshore wind, to electrolyzers. Conventional 50/60 Hz transformers and rectifiers are well established but are often heavy, bulky, and limited in performance at high power levels. Solid-state transformers, operating at higher frequencies, offer the potential to reduce system size and weight while improving functionality and efficiency.
The research is conducted within the FlexH2 project, a sponsored program that investigates new concepts for integrating offshore wind energy with onshore hydrogen production. The work presented in this thesis contributes to Work Package 2, which focuses on developing an SST based interface between the medium-voltage AC network and the DC supply of large electrolyzers. Several SST topologies, including the Modular Multilevel Converter (MMC), Resonant Modular Multilevel Converter (MMR), and Input-Series Output-Parallel (ISOP) structures, are analyzed and compared in terms of efficiency, weight, losses, and system complexity.
The main focus of the thesis is on the medium-frequency transformer (MFT), which provides galvanic isolation and voltage conversion within the SST. The study addresses key design challenges, including insulation coordination under non-sinusoidal stress, high-current busbar design, and thermal management in compact, high-power systems. Practical design procedures are proposed for both full-scale and down-scaled transformers. Experimental work on a down-scaled prototype is carried out to verify the analytical and simulation results.
The novel approach using semiconductive coatings is introduced to control electric field distribution and mitigate partial discharges within the transformer. The work also includes guidelines for applying and validating such coatings in dry-type MFT designs.