Speaker
Description
Inspired by the Levitated Dipole Experiment (LDX), Openstar proposed replacing the LTS core magnet with an HTS magnet powered by flux pumps. Embedded flux pumps enable the HTS magnet to maintain a constant DC field similar to LTS magnets with persistent joints. However, due to the limited zero-field region within the magnet, optimizing the flux pump design is critical to achieving maximum voltage and current ratings while minimizing heat leak in the system.
Existing tools for modelling magnet characteristics span various complexity levels and multi-physics couplings, including FEM, circuit modelling, and hybrid approaches. A unique challenge lies in bridging the modelling of both the transformer rectifier flux pump and the magnet under a unified framework. MATLAB/Simscape offers an unparalleled advantage by combining multi-physics capabilities with customizable components, enabling magnet models of varied complexity alongside flux pump modelling.
Independent models of the flux pump and magnet were implemented using MATLAB/Simscape and validated against experimental results. While the circuit modelling approach limits the dynamic resistance prediction, the flux pump behaviour was captured similar to experimental findings. The magnet was modelled as 14 magnetically- coupled coils (L-R circuits), providing a robust framework for system-level optimization. This enabled iterative evaluations of flux pump parameters, including transformer sizing, switch length, field amplitude, input current waveform, and frequency.
Practically, integration revealed significant variations in flux pump characteristics based on load conditions, emphasising the importance of co-modelling the flux pump with its load. The system-level model effectively replicated experimental results, including voltage waveforms, and provided insights into issues such as long charging times, heat dissipation, and current distribution under varying operating conditions.
The model facilitated the optimization of flux pump output voltage to meet the rated operation requirements of the magnet. This optimization informed critical design parameters for flux pump iterations, enhancing overall system performance and reliability.
To further enhance the model, we aim to incorporate temperature-dependent functionality for the flux pump switches and include thermal domain modelling for the magnet. The versatility of MATLAB/Simscape enables the integration of additional physics modules, paving the way for developing comprehensive digital twin models for HTS systems.
