Design of a Fuel cell/Battery Hybrid System
Translated title
Design af brændselscelle/batteri hybrid system
Author
Holm, Lars
Term
4. term
Education
Publication year
2018
Submitted on
2018-06-01
Abstract
Dette speciale udvikler og vurderer et brændselscelle/batteri-hybridsystem til en stor drone med henblik på at forlænge flyvetiden under høje effektkrav. Arbejdet tager udgangspunkt i batteriers begrænsninger for tunge UAV-opgaver og undersøger, om en hybrid kan fungere som rækkeviddeforlænger. En analyse af effekt- og energitæthed sammenligner litium-ion batteripakker med komplette brændselscellesystemer (inklusive brintlager) og viser, at en stand-alone brændselscelle har for lav effekttæthed til fremdrift, men kan være attraktiv som energikilde ved større kapaciteter. Den valgte topologi placerer brændselscellen bag en DC/DC-konverter på en fælles DC-bus parallelt med batteriet, så batteriet håndterer spidsbelastninger, og brændselscellen leverer middelbelastningen. Dimensioneringen er udført for en hovringstilstand, og under denne forudsætning giver en batterikapacitet omkring 3000 Wh den længste flyvetid. Et batteristyringssystem (BMS) er designet til at overvåge celles spændinger, strøm og temperatur, estimere ladetilstand (SoC) med to metoder—Ah-tælling og en modelbaseret OCV-tilgang—samt at lade pakken via en buck-konverter. Test viser, at under afladning er Ah-tælling den mest pålidelige SoC-metode, og en konstant-strøm-ladetest validerer laderfunktionen. Samlet set skitserer resultaterne en anvendelig kontrol- og hardwareløsning for et drone-skaleret brændselscelle/batteri-hybridsystem.
This thesis develops and evaluates a fuel cell/battery hybrid power system for a large drone to extend endurance while meeting high power demands. The work frames the design problem around the limitations of batteries for heavy-lift UAVs and assesses whether a hybrid architecture can act as a range extender. A power and energy density analysis compares lithium-ion battery packs with complete fuel cell systems (including hydrogen storage), showing that stand-alone fuel cells have insufficient power density for propulsion but can be attractive as energy providers at higher capacities. The chosen topology places the fuel cell behind a DC/DC converter on a common DC bus in parallel with the battery so the battery supplies peak loads and the fuel cell supplies average power. Sizing is performed for a hovering condition, and within this constraint a battery capacity of about 3000 Wh yields the longest flight time. A battery management system (BMS) is designed to monitor cell voltages, current, and temperature; to estimate state of charge (SoC) using two methods—coulomb (Ah) counting and a model-based open-circuit-voltage approach; and to charge the pack via a buck converter. Tests indicate that during discharge the Ah-counting method provides the most reliable SoC estimates, and a constant-current charging test validates the charger functionality. Together, the results outline a feasible control and hardware design for a drone-scale fuel cell/battery hybrid powertrain.
[This summary has been generated with the help of AI directly from the project (PDF)]
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