magistrsko delo
Nejc Mirtič (Author), Marko Jankovec (Mentor), Boštjan Glažar (Co-mentor)

Abstract

V naporih za globalni prehod na zelene vire energije je prišlo do pospešenega razvoja na področju fotovoltaike. Napredek se kaže med drugim tudi v povečevanju moči fotonapetostnih (PV) modulov, saj trenutno najmočnejši komercialno dostopni moduli dosegajo že moči preko 800 W. Razvoju morajo slediti tudi merilni sistemi, ki jih uporabljamo za spremljanje delovanja PV modulov v realnih pogojih in določanja njihovih karakteristik, energijskega izplena in življenjske dobe. Merilna oprema med drugim zagotavlja, da PV moduli med obratovanjem delujejo z največjo razpoložljivo močjo. Za to skrbi sledilnik točke največje moči oz. MPPT, kjer se za dober izkoristek pretvorbe energije uporabljajo stikalni pretvorniki v različnih topologijah, med katerimi prednjačijo zaporni pretvorniki. V tej nalogi smo si zastavili raziskovalno vprašanje, če bi bilo mogoče za potrebe MPPT obstoječe zaporne pretvornike zamenjati z resonančnim pretvorniki v LLC topologiji in s tem izboljšati izkoristek ter pripraviti bolj modularno osnovo, ki omogoča nadaljnje nadgradnje. S topologijo LLC smo želeli tudi znatno zmanjšati stikalne izgube glede na zaporni pretvornik in pri tem doseči izkoristek pretvorbe nad 93 %. Hkrati pa nas je tudi zanimalo, če lahko za LLC DC-DC pretvornik navzgor uporabimo transformator, ki je namenjen za LLC pretvornik navzdol, katerega povežemo tako, da dobi primarno navitje transformatorja vlogo sekundarnega in obratno. Klasične izvedbe stikalnih napajalnikov z vsakim stikalnim ciklom odklopijo celotni bremenski tok. To vodi do stikalnih izgub, ki se povečujejo z višanjem stikalne frekvence. Zmanjšanje stikalnih izgub najlažje dosežemo tako, da preklapljamo stikala (tranzistorje) v trenutku, ko napetost ali tok skozi stikalo preide skozi ničlo. Topologije stikalnih usmernikov kjer napetost ali tok preideta skozi ničlo (ZVS ali ZCS), najpogosteje izkoriščajo lastnosti LC-resonančnega kroga, zato jih lahko poimenujemo tudi resonančni pretvorniki. Tako smo na osnovi simulacij in podatkovnih listov načrtovali resonančni stikalni pretvornik tipa LLC. Ta ima resonančni krog sestavljen iz dveh induktivnosti (L_r in L_m) in ene kapacitivnosti (C_res). Nato smo izdelali prototipno vezje, pri katerem smo z iterativnimi izboljšavami uspeli doseči zadane cilje. Pretvornik lahko obratuje med napetostmi od 5 V in vse do 60 V in pri tem ves čas na izhodu zagotavlja napetost 250 V. Tekom testiranja smo dosegli moč 400 W, kar je sicer maksimalna moč transformatorja. Zadani izkoristek pretvorbe vezja 93 % smo dosegli, saj se je v resonančni točki vezja izkoristek gibal med 88 % in 93 %, z maksimumom pri 93,2 %. Tekom meritev smo ugotovili, da bi bilo za zamenjavo obstoječih zapornih pretvornikov znotraj MPPT naprav potrebno optimizirati delovne točke z namenom boljšega izkoristka v celotnem razponu obremenitev in napetosti in ne samo v območju nad 50 % obremenitve. Z nalogo smo tako pokazali, da je mogoče transformatorje, ki so primarno namenjeni pretvorbi navzdol, uspešno uporabiti tudi v pretvornikih navzgor.

Keywords

resonančni pretvorniki;stikalni pretvorniki;DC-DC;LLC;Buck;Boost;PV moduli;sončne celice;magisteriji;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FE - Faculty of Electrical Engineering
Publisher: [N. Mirtič]
UDC: 621.383.51(043.2)
COBISS: 137594883 Link will open in a new window
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Downloads: 14
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Other data

Secondary language: English
Secondary title: Resonant switching converter for maximum power tracking of photovoltaic modules
Secondary abstract: With the efforts for a global transition to renewable energy sources, there has been an accelerated development in the field of photovoltaics. Progress can be seen, among other things, in increasing the power of photovoltaic (PV) modules, as currently the most powerful commercially available modules already reach over 800 W. The development must also be followed by the measurement systems used to monitor the operation of PV modules in real conditions and to determine their characteristics, energy yield and lifespan. Among other things, the measuring equipment ensures that the PV modules operate with the maximum available power. This is taken care of by the maximum power point tracker or MPPT, where switching converters in different topologies are used for good energy conversion efficiency, among which flyback converters are the most prevalent. In this assignment, we asked ourselves a research question, if it would be possible to replace the existing flyback converters with resonant converters in LLC topology for use in the MPP trackers and thereby improve the efficiency and prepare a more modular base that allows for further upgrades. With the LLC topology, we also wanted to significantly reduce the switching losses compared to the rest of the switching converters and achieve a conversion efficiency of over 93%. At the same time, we were also interested in whether we can use a transformer for the LLC DC-DC boost converter, which is intended for the LLC buck-converter, which we connect in such a way that the primary winding of the transformer takes the role of the secondary and vice versa. Classic designs of switch mode power supplies disconnect the entire load current with each switching cycle. This leads to switching losses that increase with increasing switching frequency. The reduction of switching losses is most easily achieved by switching the switches (transistors) when the voltage or current through the switch passes through zero. Topologies of switching converters where the voltage or current passes through zero (ZVS or ZCS) most often take advantage of the properties of the LC resonant circuit, therefore they are broadly classified as resonant converters. Based on simulations and data sheets, we designed a resonant switching converter of the LLC topology. Which has a resonant circuit consisting of two inductances (L_r and L_m) and one capacitance (C_res). We made a prototype circuit, in which we managed to achieve the set goals through iterative improvements. The converter can operate between voltages of 5 V and up to 60 V, and at the same time provides a voltage of 250 V at the output. During testing, we achieved a power of 400 W, which is the maximum power of the transformer. The set circuit conversion efficiency of 93% was achieved, since at the resonant point of the circuit the efficiency varied between 88% and 93%, with a maximum of 93.2%. During the measurements, we found that in order to replace the existing gate converters inside the MPPT devices, it would be necessary to optimize the operating points with the aim of better efficiency in the entire range of loads and voltages and not only in the area above 50% of the load. With the paper, we have shown that transformers, which are primarily intended for step-down conversion, can also be successfully used in boost converters.
Secondary keywords: Resonant Converters;Switch mode converters;DC-DC;LLC;Buck;Boost;Photovoltaics;Solar Cells;
Type (COBISS): Master's thesis/paper
Study programme: 1000316
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za elektrotehniko
Pages: IX, 70 str.
ID: 17509551