Enosmerni presmernik z resonatorjem in trinivojsko tranzistorsko stopnjo

MARKIČ, JAN (avtor), Zajec, Peter (mentor)

V avtomobilski industriji se pojavljajo hibridna vozila, ki imajo v sistemu vsaj dve bateriji različnih napetostnih nivojev. Lahki hibridi imajo poleg 12 V baterije največkrat še 48 V baterijo. Takšen sistem vsebuje tudi enosmerni presmernik, ki povezuje oba napetostna nivoja. Cilj moje naloge je poiskati najustreznejšo topologijo za takšen sistem in simulirati njegovo delovanje v programu LT Spice. V nalogi je opisan hibridni sistem in njegove prednosti ter vloga enosmernega pretvornika v sistemu. Topologija največkrat uporabljenega kaskadnega pretvornika navzgor-navzdol ima omejitve pri višanju stikalne frekvence, saj se z njo višajo stikalne izgube. Poleg tega povzroča takšen pretvornik zaradi hitrih in velikih sprememb toka in napetosti pri trdem preklapljanju zelo velike elektromagnetne motnje. V nadaljevanju so predstavljene izgube na stikalnih MOSFET tranzistorjih in možnosti za dvig izkoristka pretvornikov. Ena od teh je vpeljava mehkih preklopov, kar dosežemo z drugačno topologijo ali s kompleksnejšim krmiljenjem. Iskal sem rešitev z uporabo topologije večnivojskega pretvornika z ločilnimi diodami in resonatorjem ter v nalogi predstavil njegove prednosti in slabosti. Razloženo je delovanje takšnega pretvornika in primerjava izgub s kaskadnim pretvornikom na podlagi simulacij. Izkaže se, da ima večnivojski pretvornik slabši izkoristek zaradi večjega števila elementov, ki povzročajo večje prevodne izgube. Ima pa nekatere prednosti, kot so manjše stikalne izgube, manjši porasti napetosti na tranzistorjih in manjše elektromagnetne motnje. Kljub temu, je za lahke hibride kaskadni pretvornik navzgor-navzdol boljša rešitev, saj lahko s kompleksnim proženjem prav tako zagotovimo mehke preklope. Hkrati ima takšen pretvornik tudi višji izkoristek in manjše število elementov.

• Jezik: Slovenski jezik
• Ključne besede: enosmerni pretvornik, večnivojski pretvornik, resonator, izgube na tranzistorjih, mehko preklapljanje, lahek hibridni sistem
• Vrsta gradiva: Magistrsko delo/naloga
• Organizacija: FE - Fakulteta za elektrotehniko
• Leto izida: 2018
• PID: 20.500.12556/RUL-99915
• Datum objave v RUL: 21.02.2018

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: DC/DC converter with resonator and three-level transistor stage

Izvleček

Modern car industry is developing hybrid vehicles, which have two batteries with different voltages. Mild hybrid vehicles have typically a smaller 12 V battery and a larger 48 V battery. In such electric system there is a DC/DC converter, which connects both voltage levels and allows energy transfer from one to another battery. The purpose of this master thesis is to find the best topology for the DC/DC converter and to analyze its operation based on simulations using LT Spice program. Typical hybrid system, its advantages and role of the DC/DC converter are described in this paper. Most frequently used topology of a cascaded buck-bust converter has its limits, when we want to increase switching frequency. Hard switching of transistors produces very big electromagnetic interference, because of fast and rapid changes of current and voltage in the circuit. Further on losses of switching MOSFETs and possibilities for improving the converter efficiency are presented. One of the possibilities is introduction of soft switching, which can be realized by a different topology or with a more complex MOSFET driving technique. Solution based on a topology of a multilevel converter with separating diodes and a resonant circuit was selected for investigation. Its advantages and disadvantages are described in this work. The operation of multilevel converter and comparison to a cascaded converter are presented and explained based on the simulations. It turns out, that the multilevel converter for the selected voltages operates with lower efficiency. This is because the number of elements in the circuit, which produce conduction losses is bigger. It also has some advantages like lower switching losses, smaller voltage on transistors and consequently lower EMC. Nevertheless, for a mild hybrid system with rather low voltages cascaded buck-boost converter is a better solution for achieving higher efficiency. Soft switching can also be achieved with a complex MOSFET driving technique. On top of that, it also has a smaller number of elements, which reduces the manufacturing cost.

• Ključne besede: DC/DC converter, multilevel converter, resonant circuit, losses in MOSFET transistors, soft switching, mild hybrid system