Ward, Oliver MG; (2025) Dynamic Simulation and Design Optimisation of Power Conversion Systems for a Pulsed Fusion Power Plant. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The UK Atomic Energy Authority is leading the Spherical Tokamak for Energy Production (STEP) project to design and build a power plant that demonstrates net electricity generation from nuclear fusion. Due to challenges with tokamak operation, prototype fusion power plants may be operated in a pulsed regime. Additionally, thermal heat will be distributed to multiple tokamak components at different temperatures. Both of these complicate the design of the power conversion system. Components, like turbines, are sensitive to stresses from thermal transients. Heat sources must be integrated to utilise all available heat efficiently for net electrical power generation to be feasible. In this thesis, an optimisation methodology based on dynamic process models is developed to address this design challenge. Dynamic models of possible power conversion systems for pulsed fusion power plants are developed using novel dynamic heat exchanger models made with computational complexity and ease of automated simulation in mind. Thermal energy storage is considered as a solution to the pulsed tokamak operation. These models are then used within the objective functions of multiple optimisation problems. The optimal tuning of a load following proportional-integral-derivative controller is considered for a system with a constant heat source. The optimised controller shows large error reductions at the cost of increased low amplitude oscillations due to over-tuned integral action. The trade-off between thermal energy storage system size and fraction of nominal power output during a dwell is considered as a bi-objective optimisation problem for a tokamak with one or three pulsed heat sources. Both case studies show the potential for significant size reductions, but these designs lead to issues with low molten salt temperatures. The methodology is shown to generate good designs within the constraints of a fixed process configuration, and could be extended to the design of other transient processes.

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