Parameter sensitivity analysis and model-based design of experiments of the analytical model for impedance of the proton exchange membrane fuel cell

Elektrokemična impedančna spektroskopija (EIS) je izjemno uporabno orodje za in situ meritve in modeliranje gorivnih celic (GC). Navkljub raziskovalnim naporom na področju EIS modeliranja velik izziv pri uporabi metode povzroča interpretacija merilnih rezultatov, saj fizikalnokemijsko konsistentni modeli, ki uporabljajo parametre s fizikalnim pomenom še niso razviti v dovoljšni meri. Z namenom pospešitve razvoja na tem področju je v delu opisana implementacija fizikalno konsistentnega analitičnega modela v frekvenčni domeni, ki je veljaven za vse gostote električnega toka in obravnava anodo in katodo GC. Razvit model smo inovativno sklopili z modelom v časovni domeni, ki izkazuje zelo dobre napovedne lastnosti. Sklopitev daje kvalitetnejše informacije o intrinzičnih parametrih GC, kot bi jih lahko pridobili zgolj v posamezni domeni. Model smo verificirali in validirali, preverili možno redukcijo modela in izvedli optimalni dizajn eksperimentov (DoE) z analizo frekvenčne občutljivosti kalibracijskih parametrov in vplivnosti obratovalnih pogojev. Rezultati kažejo, da ima model dobro sposobnost kalibracije na eksperimentalne podatke, vrednost R-kvadrat je namreč vedno večja od 0,965, model ima tudi dobre ekstrapolacijske lastnosti. Z DoE smo pokazali, da je z majhnim številom dobro nastavljenih eksperimentov možno bistveno izboljšati pridobljeno informacijo o kalibracijskih parametrih. Poleg tega predlagano metodologijo uporabimo z namenom zmanjšanja potrebnega števila meritev impedančnih spektrov za doseganje zadostne informacije o posameznih kalibracijskih parametrih.Electrochemical impedance spectroscopy (EIS) is an extremely important tool for in-situ measurements and modelling of fuel cells (FC). Despite long research efforts in the field of EIS modelling, the interpretation of experimental data remains a challenge as physicochemically consistent models, which use parameters with a clearly defined physical meaning, have no yet to be fully developed. With the purpose of accellerating the developement in this field, in this thesis an implementation of such a physically consistent model is described. The model is valid for all current densities and takes into account the cathode and the anode side of the FC. The developed model was interconnected with a time domain model with state-of-the-art extrapolation capabillities. The model was verified and validated, reduced versions of the model were tested for accuracy and optimal design of experiments (DoE) was conducted. In addition, an analysis of sensitivity of calibration parameters with respect to frequency was conducted and the influence of each seperate operational condition was asessed. The results show a high accuracy of fit as the R-squared parameter never falls below 0.965. The model also shows good extrapolation capabilities. DoE has shown that experiments with fewer measurements can yield much higher information of calibration parameters if they are meticulously planned. This proposed methodology is used with the aim of reducing the number of required measurements of impedance spectra for acquiring a sufficient ammount of information about individual calibration parameters

Comparison of Systems for Solar Electricity Production

V nalogi smo raziskali možnosti izrabe energije Sonca za proizvodnjo električne energije v majhnih postrojih, ki so sestavni – integralni del objektov. Z uporabo podatkov in metod iz literature smo določili potencial sončnega sevanja za poljubno mikrolokacijo z upoštevanjem geografskih, topoloških, in meteoroloških pogojev. Primerjali smo dve tehnologiji za pretvorbo sončne energije v električno energijo: fotonapetostne pretvornike in termični solarni sistem z uporabo krožnega procesa. Na podlagi vrednotenja skupnega energijskega izkoristka ter tehnoloških značilnosti obeh sistemov smo ugotovili, da je fotonapetostni sistem boljši, kar odraža tudi praksa.In this thesis we asses the possibility of using the energy of the Sun for the production of electricity in small-scale systems, which are integrated into buildings. With the use of data and methods from literature we defined the energy potential of solar radiation for a desired microlocation, taking into account the influence of geographical, topological and meteorological factors. We compared two different technologies for converting solar radiation into electricity: photovoltaic converters and a thermal solar system that utilizes a thermodynamic cycle. Upon evaluating the effective energy efficiency and technological characteristics we found that photovoltaics are superior to the thermal solar system for small-scale utilization, whics is also confirmed in practice

Hybrid methodology for parametrisation of proton exchange membrane fuel cell model for diagnostics and control applications

Electrochemical impedance spectroscopy (EIS) is a very powerful tool for the diagnosis and characterisation of fuell cells (FC). However, there is still a lack of physico-chemically consistent models that include parameters with a clear physical meaning and can be related to intrinsic parameters of FC. To fill this knowledge gap, this paper presents a novel, mechanistically-based and computationally-efficient FC modeling framework for time and frequency domain simulations. Furthermore, the model consistently handles forward and backward reactions, ensuring its validity at all current densities. These features enable the development of a hybrid methodology for parameterising the FC model in both domains, resulting in unprecedented accuracy in determining the internal states around which the EIS perturbation is applied. Furthermore, innovative modeling framework incorporates a 1D analytical solution of FC impedance that for the first time accounts for both electrodes, the membrane and individual effects of the electrodes coupled to the respective GDL and channel, all significantly impacting the accuracy of the model. This was confirmed by state-of-the-art reproduction of experimental data with R$^2$ values exceeding 0.965 for data not used in the parameterisation. The presented modeling framework thus provides a modelling basis for observer functionalities beyond the state-of-the-art