Design and control of multiport isolated DC-DC converter for hydrogen energy systems

Oyewole, Oyedotun E.

Thesis

Design and control of multiport isolated DC-DC converter for hydrogen energy systems

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Creator

Oyewole, Oyedotun E.

Rights statement

Strathclyde Thesis Copyright

Awarding institution

University of Strathclyde

Date of award

2026

Thesis identifier

T17688

Person Identifier (Local)

202263467

Qualification Level

Doctoral (Postgraduate)

Qualification Name

Doctor of Philosophy (PhD)

Department, School or Faculty

Abstract

Hydrogen energy storage systems (HESS) are vital for sustainable energy, and their performance is heavily influenced by their power electronics converter (PEC) interfaces. Conventional PEC interfaces, which use individually operating converters, often lead to bulky systems with multiple conversion stages and increased circulating currents, resulting in higher losses. This thesis addresses these shortcomings by implementing a multiportisolated DC-DC converter for HESS, which offers enhanced power density, a reduced component count, and fewer conversion stages. However, this proposed converter introduces its own challenges, primarily the cross-coupling effect caused by the high-frequency multiwinding transformer. This effect results in significant power deviations during step changes, risking hydrogen depletion in fuel cells and instability in electrolysers. Furthermore, the conventional single-phase shift (SPS) modulation used in such converters typically experiences higher circulating currents, reducing overall efficiency. To mitigate the cross-coupling, the implementation of a decoupling control technique is essential. This study investigates and compares three simple matrix-based decoupling techniques, finding the inverse matrix method to be the best performer, though it still fails to fully decouple the system over a wide operating range. To overcome this limitation, a novel model reference-based decoupling control technique is proposed, which minimises the error between the actual system output and an ideal reference model. This technique is further enhanced into a hybrid decoupling control by integrating a decoupling matrix, ensuring robust performance across a wider operating region by mathematically minimising the crosscoupling term with a proportional-derivative controller. This hybrid technique significantly reduces maximum power deviations compared to the best matrix-based method. Recognizing that these decoupling techniques generally require detailed system knowledge, which complicates implementation due to parameter fluctuations, the thesis also proposes a solution using a linear active disturbance rejection controller (LADRC), which only requires knowledge of the system order. However, as the LADRC is susceptible to estimation errors and requires manual tuning, a particle swarm optimisation (PSO) algorithm is employed to automatically determine the optimal controller gains. This PSO-optimised LADRC effectively suppresses cross-coupling across a wider operating region, performing better than both non-decoupled controllers and a genetic algorithm (GA)-optimised LADRC. In parallel, to address the efficiency limitations of SPS control, which is limited in its ability to independently regulate inter-port power flow and leads to increased inductor current and circulating power, the thesis also proposes an online adaptive control based on the steepest descent method. This technique dynamically adjusts internal phase shifts in real-time to minimise the error between reference and actual active inter-port power flows under varying conditions, thereby enhancing operational efficiency. A comprehensive mathematical formulation, supported by Lyapunov-based stability analysis, confirms the stability of the adaptive gains in this proposed control. Finally, simulations and experimental validations confirm the effectiveness and robustness of all the proposed control techniques, demonstrating significant improvements in system efficiency and performance across a wider operating region for hydrogen energy storage applications.

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