Modelling and optimization of linear-motion kinetic energy harvesters: two approaches

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dc.contributor.advisorNiesler, Thomasen_ZA
dc.contributor.authorStruwig, Michaelen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.en_ZA
dc.date.accessioned2023-03-06T08:17:39Zen_ZA
dc.date.accessioned2023-05-18T07:16:14Zen_ZA
dc.date.available2023-03-06T08:17:39Zen_ZA
dc.date.available2023-05-18T07:16:14Zen_ZA
dc.date.issued2023-03en_ZA
dc.descriptionThesis (PhD)--Stellenbosch University, 2023.en_ZA
dc.description.abstractENGLISH ABSTRACT: Energy harvesting is a well-established method for extending the life of battery-powered devices, such as wildlife tracking collars. However, the operating conditions of these devices provide a number of challenges, such as size and weight constraints. They are also typically exposed to the non-harmonic forms of mechanical motion associated with animal footsteps. This renders much of the existing literature inapplicable, because it applies only to harmonic excitation. We propose a microgenerator architecture that consists of a variable number of evenly spaced magnets, forming a fixed assembly that is free to move through a series of evenly spaced coils, and is supported by a magnetic spring. Based on this architecture, we develop two microgenerator design approaches, each with their own electro-mechanical system model and optimization philosophy. The first approach assumes idealized (constant velocity) motion as a proxy for optimizing for the true, non-harmonic motion. We applied this method to design an optimal energy harvester for impulsive motion, resulting in a device with a length of approximately 125 mm and tube diameter of 11 mm that generated an average power of 3.01 mW in a 40 Ω test load from a 2.2 g impact force from a walking human test subject. The same method was applied to design a 85 mm length-constrained device, which was subsequently field-tested on a wild rhinoceros. When the animal walked slowly, this device generated an average of 0.342 mW. The second approach is based on an extended time-domain system model that, after an evolutionary parameter search, can predict the temporal behaviour of a microgenerator to within 25% of the measured load voltage RMS, for any chosen input excitation. Utilizing this model, we propose an enhanced optimization process that selects a set of energy harvester design parameters that maximizes the power delivered to a resistive load, resulting in an optimized device that is specific to any choice of input excitation. The resulting optimal design has a length of approximately 135 mm and a tube diameter of 11 mm and was found to deliver an average power of 1.526 mW to a 30 Ω load when driven by a less vigorous human footstep-like motion with a 1.5 g impact force. Finally, we introduce an open-source declarative energy harvester framework, FFS, and demonstrate how it can be used to design, simulate and optimize their energy harvester models.en_ZA
dc.description.abstractAFRIKAANS OPSOMMING: Energie-ontginning is ‘n bestaande metode om die batteryleeftyd van toestelle, soos halsbande om wild op te spoor, aan te vul. Die werktoestande waarbinne so ‘n toestel moet funksioneer bied egter uitdagings, soos byvoorbeeld beperkinge op die grootte en gewig van die toestel. Die toestel word gewoonlik blootgestel aan die nie-harmoniese, meganiese beweging van diere. Die bestaande literatuur is daarom nie van toepassing nie, aangesien slegs harmoniese beweging voorheen bestudeer is. Ons stel gevolglik ‘n mikrogenerator-argitektuur voor wat bestaan uit ‘n verstelbare reeks magnete wat vas aan mekaar en eweredig versprei is, en wat vrylik deur ‘n aantal spoele kan beweeg wat ook eweredig versprei is. Die opstelling word ondersteun deur ‘n magnetiese veer. Op grond van hierdie argitektuur stel ons twee benaderings voor tov. die ontwerp, elk met sy eie elektromeganiese stelselmodel en optimaliseringsfilosofie. Die eerste benadering aanvaar ge¨ııdealiseerde (konstante snelheid) beweging in plaas van die werklike, nie-harmoniese beweging. Ons het hierdie benadering toegepas om ‘n optimale energieontginner te ontwerp vir impulsbewegings. Die resultaat is ‘n toestel wat ongeveer 125 mm lank is, met ‘n buisdeursnee van 11 mm, en wat ‘n gemiddelde 3.01 mW aan ‘n 40 Ω toetslas lewer gegewe ‘n 2.2 g trefkrag wat deur ‘n lopende, menslike proefpersoon geskep word. Dieselfde metode is ook toegepas om ‘n toestel te ontwerp waar die lengte tot 85 mm beperk is. Hierdie toestel is getoets op ‘n wilde renoster. Wanneer die renoster stadig loop het die toestel ‘n gemiddeldde drywing van 0.342 mW gelewer. Die tweede benadering is gegrond in ‘n uitgebreide tydsgebied-model wat, na ‘n evolusionˆere parametersoektog, die tydsgebied-gedrag van ‘n mikrogenerator vooruit kan skat tot binne 25% van die werklik gemeette RMS spanning, vir enige gegewe inset-opwekking. Deur van hierdie model gebruik te maak stel ons ‘n optimaliseringsproses voor wat ‘n stel parameters kies sodat die drywing aan ‘n las gemaksimeer word. ‘n lengte van ongeveer 135 mm, ‘n buisdeursnee van 11 mm, en lewer gemiddeld 1.526 mW drywing aan ‘n 30 Ω las wanneer minder energieke menslike bewegings met ‘n trefkrag van 1.5 g gebruik word. Laastens stel ons FFS, ‘n oopbron, deklaratiewe sagtewareraamwerk bekend. Ons demonstreer hoe dit gebruik kan word om energie-ontginners te ontwerp, te simuleer, en te optimaliseer.af_ZA
dc.description.versionDoctorateen_ZA
dc.format.extentvii, 104 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/127326en_ZA
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectModelling and optimization of linear-motion kinetic energy harvesters: two approachesen_ZA
dc.subject.lcshEnergy harvestingen_ZA
dc.subject.lcshKinematicsen_ZA
dc.subject.lcshOptimisationen_ZA
dc.titleModelling and optimization of linear-motion kinetic energy harvesters: two approachesen_ZA
dc.typeThesisen_ZA
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