Modelling the broadband impedance of a lithium-ion battery cell using the pseudo-random impulse sequence perturbation

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dc.contributor.advisorMwaniki, Freden_ZA
dc.contributor.authorMoyo, Zandileen_ZA
dc.contributor.otherStellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.en_ZA
dc.date.accessioned2023-11-24T06:38:25Zen_ZA
dc.date.accessioned2024-01-08T11:37:48Zen_ZA
dc.date.available2023-11-24T06:38:25Zen_ZA
dc.date.available2024-01-08T11:37:48Zen_ZA
dc.date.issued2023-12en_ZA
dc.descriptionThesis (MEng)--Stellenbosch University, 2023.en_ZA
dc.description.abstractENGLISH ABSTRACT: Lithium-ion (Li-ion) batteries are becoming increasingly important for integrating renewable energy sources such as solar and wind into the electrical grid. Battery Energy Storage Systems (BESS) using Li-ion batteries address challenges posed by renewable energy, such as unpredictability and non-dispatchability, thus enhancing grid reliability. Before implementing Li-ion cells in BESS, thorough investigation and optimisation are essential. Accurate prediction of remaining useful life and State-of-Health (SOH) under varying conditions, such as temperature and State-of-Charge (SOC), is vital for effective battery management. Battery impedance, which is frequency-dependent, significantly impacts SOH and SOC, especially in the 1 Hz to 1 kHz range. Therefore, modelling the broadband impedance of the Li-ion battery helps to improve battery management and reliable operation. Accurate battery cell modelling also enables system integrators to perform effective network simulations. The impedance of a Li-ion battery is often computed from its response voltage and current signals to an injected excitation signal. This thesis uses the novel Pseudo-random Impulse Sequence (PRIS), a broadband bipolar excitation signal, for Li-ion battery impedance measurements. The PRIS excitation source is optimised, by tuning its series resistor, inductor and capacitor (RLC) network components and Direct Current (DC) voltage input, to ensure sufficient spectral energy for impedance testing without damaging the battery. The impedance is determined from the battery’s excitation response voltage and current signals using Fourier techniques. An excitation method is proposed for accurate Li-ion cell impedance measurements. This method involves separating the desired frequency range into multiple bands that are perturbed separately using optimised excitation parameters to improve the measurement signal-to-noise ratio, reduce variance, and minimise bias. Parameter Estimation (PE) techniques, via the physics-based Equivalent Circuit Model (ECM) approach, are used to characterise and model Li-ion battery cell impedance. A simulated PE is performed in MATLAB, while a PE using physical experimental data is performed in ZView software. The SOC of the Li-ion cell is varied through discharge tests, and the cell impedance is measured at each SOC using the proposed excitation method. This research demonstrates that the optimised PRIS source and the proposed excitation method improve the accuracy of the measurement of the Li-ion battery impedance, thus enhancing the performance of battery modelling. The excitation responses of the validated Li-ion battery cell model, from PE, closely match the actual system responses across all relevant frequencies. The influence of SOC on impedance is effectively observed, especially at mid to lower frequencies. This thesis confirms that the PRIS and the proposed excitation method are suitable for Li-ion battery impedance measurements and modelling. It is evident that the PRIS excitation signal, along with the proposed method, results in good Li-ion cell impedance measurements with minimal noise and bias. This leads to reliable estimation of the ECM parameters that replicates the physical responses of the battery at varying SOC, thus benefiting future simulations and system integration.en_ZA
dc.description.abstractAFRIKAANSE OPSOMMING: Litium-ion (Li-ion) batterye word toenemend belangrik vir die integrasie van hernubare energiebronne soos sonkrag en wind in die elektriese netwerk. Batterye-energiebergingstelsels (BESS) wat Li-ion batterye gebruik, spreek uitdagings aan wat deur hernubare energie gestel word, soos onvoorspelbaarheid en nie-afroepbaarheid, en verbeter sodoende die betroubaarheid van die netwerk. Voordat Li-ion selle in BESS ge¨ımplementeer word, is ’n deeglike ondersoek en optimisering noodsaaklik. Akkurate voorspelling van oorblywende bruikbare lewensduur en Toestand-van-Gesondheid (TVG) onder wisselende toestande, soos temperatuur en Laadtoestand (LT), is noodsaaklik vir doeltreffende batterjbestuur. Batterjie impedansie, wat frekwensie-afhanklik is, be¨ınvloed TVG en LT beduidend, veral in die 1 Hz tot 1 kHz reeks. Daarom dra die modellering van die bre¨eband impedansie van die Li-ion-battery daartoe by om batterjbestuur en betroubare werking te verbeter. Akkurate modellering van batterjiensell stel ook sisteemintegrators in staat om doeltreffende netwerksimulasies uit te voer. Die impedansie van ’n Li-ion batterye word dikwels bereken uit sy respons-spanning en stroom seine op ’n ingespoten opwekkingssein. Hierdie tesis gebruik die nuwe Vals-Willekeurige Impulsreeks (VWIR), ’n bre¨eband bipolˆere opwekkingssein, vir Li-ion batterjie impedansiemetings. Die VWIR opwekkingsbron is geoptimeer deur sy reeksw weerstand, induktor, en kapasitor (WIK) netwerk komponente, en Gelykstroom (GS) spanning insette af te stel, om voldoende spektrale energie vir impedansietoetse te verseker sonder om die batterjie te beskadig. Die impedansie word bepaal uit die batterjie se opwekkingsrespons-spanning en stroom seine deur Fourier tegnieke te gebruik. ’n Opwekkingsmetode word voorgestel vir akkurate Li-ion selimpedansiemetings. Hierdie metode behels die skeiding van die gewenste frekwensiereeks in meervoudige bande wat afsonderlik deur geoptimeerde opwekkingsparameters versteur word om die meetings sein-tot-ratsio, variasie, en vooringenomeheid te verbeter. Parameterbepaling (PB) tegnieke, via die fisika-gebaseerde Ekwivalente Sirkuit Model (ESM) benadering, word gebruik om die impedansie van Li-ion batterjiesselle te kenmerk en modelleer. ’n Gesimuleerde PB word in MATLAB uitgevoer, terwyl ’n PB met fisiese eksperimentele data uitgevoer word in ZView sagteware. Die LT van die Li-ion sel word gewissel deur ontlaaistoetse, en die selimpedansie word by elke LT gemeet met die voorgestelde opwekkingsmetode. Hierdie navorsing toon dat die geoptimeerde VWIR bron en die voorgestelde opwekkingsmetode die akkuraatheid van die meting van die Li-ion batterjie impedansie verbeter, en sodoende die prestasie van batterjimodellering. Die opwekkingsrespons van die gevalideerde Li-ion batterjiemodel, van PB af, stem naby ooreen met die werklike sisteemrespons by alle relevante frekwensies. Die invloed van LT op impedansie word effektief waargeneem, veral by medium tot lae frekwensies. Hierdie tesis bevestig dat die VWIR en die voorgestelde opwekkingsmetode geskik is vir Li-ion batterjie impedansiemetings en modellering. Dit is duidelik dat die VWIR opwekkingssein, saam met die voorgestelde metode, lei tot goeie Li-ion selimpedansiemetings met minimale ruis en vooringenomeheid. Dit lei tot betroubare raming van die ESM parameters wat die fisiese respons van die batterjie by wisselende LT naboots, en sodoende toekomstige simulasies en sisteemintegrasie ten goede kom. en_ZA
dc.description.versionMastersen_ZA
dc.format.extentxix, 136 pages : illustrationsen_ZA
dc.identifier.urihttps://scholar.sun.ac.za/handle/10019.1/128801en_ZA
dc.language.isoen_ZAen_ZA
dc.language.isoen_ZAen_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subject.lcshLithium ion batteriesen_ZA
dc.subject.lcshRenewable energy sourcesen_ZA
dc.subject.lcshImpedance (Electricity)en_ZA
dc.subject.lcshBattery management systemsen_ZA
dc.subject.lcshPseudo-random impulse sequenceen_ZA
dc.titleModelling the broadband impedance of a lithium-ion battery cell using the pseudo-random impulse sequence perturbation en_ZA
dc.typeThesisen_ZA
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