بررسي و ساخت مبدل بسيار كاهنده غير ايزوله كليدزني نرم

چكيده انگليسي :

Analysis and implementation of a non isolated soft switched high step down converter Siamak Khalili siamak khalili@ec iut ac ir June 22 2020 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Prof Hosein Farzanehfard hosein@cc iut ac ir Abstract Today there are a lot of Electronic devices which need low input voltage and high input current To providethese levels of voltage and current step down and high step down converters include isolated and non isolated convertersshould be used In isolated converters weight value and loss are large that decrease efficiencies Thus when isolation isnot necessary using non isolated converters is preferred Buck converter is one of the most popular converters in step downapplications however it suffers from narrow duty cycle high voltage stress on semiconductors output current ripple andhigh losses To resolve these problems using some techniques such as interleaved converters to reduce output inductorcurrent ripple and some other techniques to extend duty cycle provides soft switching condition to decrease switching lossof semiconductor elements and improves efficiency In this thesis at first challenges of step down applications are discussed In the following some step down and high step down converters are introduced their advantages and disadvantages are illustrated and also to resolve some defects of thesestopologies some alternative topologies are presented Moreover some proper techniques are used and completely analyzedto extend duty cycle of introduced topologies Then in this thesis some novel topologies are proposed By using interleavingconverters technique and dividing of their input voltage a high step down interleaved converter with coupled inductorproposed By changing the proposed converter not only duty cycle is extended but also stress voltage on semiconductorelements is decreased Furthermore by using passive clamp circuits voltage spike on main switches of converter whichexists because of leakage inductors of coupled inductors is eliminated To resolve defects of converters in high step downapplications a high step down converter is proposed which is a combination of Buck and Cuk converters with lower stressvoltage on semiconductor elements than input voltage By combining this proposed converter with a passive snubber cell soft switching condition is provided for all semiconductor elements Therefore a high step down converter with losslesssnubber cell is presented Efficiency of the Buck Cuk converter with passive lossless snubber is higher than hard switchedversion of the proposed converter In the following by changing structure of the proposed Buck Cuk converter and replacingthe output diode with a switch without adding any additional element soft switching condition at zero voltage is provided forall switches during turning on and off By eliminating switching loss and capacitive turn on loss and decreasing conductionloss efficiency of the proposed converter is improved significantly Another advantage of proposed improved Buck Cukconverter is low voltage stress on all switches In line with thesis purposes by changing structure of primary Buck Cukconverter and adding an inductor and a diode to output of the converter the interleaved version of the Buck Cuk converter ispresented By adding tapped inductor and also using WCCI technique beyond increasing conversion ratio voltage stress ofsemiconductor elements is reduced too Also output current ripple is decreased In this thesis operations of the presentedconverters are completely discussed and analyzed Besides all results are confirmed and verified with simulation andexperimental prototype results Key Words 1 High step down converter 2 Non insulated DC DC converter 3 Soft switching 4 Extended duty cycle

خليلي، سيامك

بررسي و ساخت مبدل بسيار كاهنده غير ايزوله كليدزني نرم

مبدل بسيار كاهنده , مبدل DC − DC غير ايزوله , كليدزني نرم , ضريب وظيفه توسعه يافته