Electromagnetic Finite Element Analysis and Simulation-Based Design Optimisation of Busbar
Authors
Dyring, Terkel Føns ; Jakobsen, Zacharias Møller
Term
4. term
Education
Publication year
2025
Submitted on
2025-05-30
Pages
61
Abstract
Power converters in offshore wind turbines use over a ton of copper in busbars—solid copper bars that route electricity. With AC, skin and proximity effects push current toward the surface, so much of the cross-section is underused. This work redesigns a three-dimensional copper busbar to reduce mass while keeping Joule (heat) losses low. We analyze the actual switching current waveforms in PLECS and identify the frequency components that drive losses, validating that their RMS components (a measure linked to heating) match in time and frequency domains. These components feed quasi-static finite element electromagnetic simulations in COMSOL that solve Maxwell’s equations and include inductive effects. A transient model is validated by pulse tests on a reference busbar with cutouts, where Rogowski coils (current sensors) measure how current shares between parallel paths over time. We then explore the design space, trading targeted topology changes against mass, Joule losses, and surface area via an objective function evaluated from COMSOL results. Because temperature depends on both losses and available cooling surface—and the busbar is force-cooled—we consider a loss-to-area ratio, since more surface area can dissipate more heat. The best partial redesign is extrapolated to the full geometry. Finally, a coupled model combining electromagnetic loss calculation, heat transfer, and computational fluid dynamics (CFD) compares thermal performance and accounts for copper’s temperature-dependent resistance. The final design significantly reduces mass and increases surface area; although AC resistance raises electrical losses, the larger area improves cooling, leading to a lower steady-state temperature than the reference busbar.
Strømkonvertere i havvindmøller bruger over et ton kobber i samleskinner—massive kobberstænger, der leder strømmen. Ved vekselstrøm tvinger skin- og nærhedseffekter strømmen ud mod overfladen, så store dele af tværsnittet udnyttes dårligt. Dette projekt redesigner en tredimensionel kobbersamleskinne for at reducere massen, samtidig med at Joule-tab (varmetab) kun øges minimalt. Vi analyserer de faktiske skiftestrømformer i PLECS og udpeger de frekvenskomponenter, der driver tabene, og validerer, at deres RMS-komponenter (et mål knyttet til opvarmning) er ens i tids- og frekvensdomæne. Disse komponenter bruges i kvasi-statiske elektromagnetiske finit-element-simuleringer i COMSOL, der løser Maxwells ligninger og medtager induktive effekter. En transient model valideres med pulsforsøg på en referencesamleskinne med udskæringer, hvor Rogowski-spoler (strømsensorer) måler, hvordan strømmen fordeler sig i parallelle veje over tid. Modellen bruges derefter til at afsøge designrummet, hvor delvise topologiændringer afvejes mod masse, Joule-tab og overfladeareal via en målfunktion baseret på COMSOL-resultater. Da temperaturen afhænger af både tab og overflade til køling—og skinnen er tvangskølet—indføres et forhold mellem tab og areal, fordi større overflade kan aflede mere varme. Den bedste del-løsning overføres til hele geometrien. Til sidst sammenligner en koblet model, der kombinerer elektromagnetiske tab, varmetransport og beregningsfluiddynamik (CFD), den termiske ydeevne og tager højde for kobbers temperaturafhængige modstand. Det endelige design reducerer massen markant og øger overfladen; selv om AC-modstanden giver flere elektriske tab, forbedrer det større areal kølingen, så driftstemperaturen bliver lavere end for referenceskinnen.
[This apstract has been rewritten with the help of AI based on the project's original abstract]
Keywords