Electromagnetic Finite Element Analysis and Simulation-Based Design Optimisation of Busbar

Dyring, Terkel Føns ; Jakobsen, Zacharias Møller

4. term

Electro-Mechanical System Design, Master

2025

2025-05-30

61 pages

In MW-size converters used for offshore wind turbines, more than a tonne of copper is used for the conduction of electricity. The busbars used for this purpose are often simple, solid geometries. The skin and proximity effect, which are inductive effects from AC current, cause the current to flow near the surface of the conductor, meaning that the cross sections are poorly utilised. A three-dimensional copper busbar is redesigned with the intention of reducing the overall volume of the part while keeping a minimal increase in Joule losses. The current waveforms which the busbar is subject to are analysed and simulated in PLECS, as the power module switching frequency significantly affects the waveform. The frequencies that cause the highest Joule losses are selected and verified to have the same RMS components in the time and frequency domain. These frequency components are used as input in quasi-static electromagnetic Finite Element Method simulations using COMSOL Multiphysics. This model solves Maxwell’s equations, including the inductive effects for the given frequencies and currents. A transient model using the same physics interface is compared and verified with a pulse test of the reference busbar with cutouts in the geometry allowing the measurement of current running in different parallel paths of the busbar using Rogowski coils, to investigate the propagation of the current through the material over time. The model is used in a design space exploration where the busbar is swept through various qualitatively selected partial changes in topology of the busbar, with the aim of finding a compromise solution between increases in Joule losses and mass reduction. The Joule losses are dependent upon current and AC resistance, which becomes difficult to estimate for nontrivial 3D structures. The explicit results from COMSOL are therefore used to assess an objective function, which evaluates the reduction of mass, Joule losses, and surface area. Since temperature development is a function of Joule losses and surface area, a loss-area ratio is set up, as more surface area will mitigate excessive heating from Joule losses since the busbar is subject to forced cooling. The design which best satisfies the objective function is extrapolated to the entire busbar geometry. To compare the thermal performance of this extrapolated design to the reference busbar, as well as the non-linear temperature-dependent resistance of copper, a heat transfer model is developed. This combines an electromagnetic model for Joule losses, a heat transfer model for temperature development, and a computational fluid dynamics model for modelling airflow and convection. The final design achieves a large improvement in mass and surface area, albeit with an increase in Joule losses mainly due to increased AC resistance. However, the heat transfer model shows that this new design converges at a lower temperature than the reference busbar, because of the increase in surface area.

Busbar ; Elektromagnetisme ; FEA

Download
View record in AAU Student Projects