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چكيده انگليسي :

Design and Implementation of a Zero Voltage Transition Forward Converter with a Simple Gate Driver Monireh Ghorbanian monireh ghorbanian@ec iut ac ir July 26 2020 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Persian Supervisor Prof Hosein Farzanehfard hosein@cc iut ac ir Abstract Single switch Forward converter is widely used in low power applications due to its circuit and control simplicity andlower required components especially switch Moreover the output current of forward converter is not pulsating and it issuitable for low output current ripple applications The core reset of the forward transformer is a significant problem whichis generally solved by using a tertiary winding However this increases the volume and cost and also limits the duty cycle The second basic problem in the conventional forward converter is hard switching ZVT auxiliary circuits provide zero voltage at turn on for the main switch The evaluation criterias of ZVT cells include soft switching of both main and auxiliaryswitches voltage and current stress of the auxiliary and main switches efficiency and applicability to other converters Inthis thesis at first existing soft transition forward converters with their advantage and disadvantage are investigated Then a new ZVT forward converter is proposed in which ZVS conditions for the main switch and ZCS condition for the auxiliaryswitch is provided In addition by eliminating capacitive turn on loss of the main switch and eliminating the reverse recoveryloss of all diodes due to ZCS turn off the efficiency of the presented converter has increased In addition the voltage stressacross the auxiliary switch is clamped to the input voltage In the proposed converter no isolated gate drivers are requiredfor the main and the auxiliary switches while the converter is PWM The primary windings of the forward converter isutilized to transfer power from the input to the output providing ZVS condition for main switch recovering the energy ofthe leakage inductance and the snubber capacitance to the output load and also the core reset of the power transformer Asa result the tertiary winding is omitted In the introduced converter the power transformer is discharged during a resonanceprocess and provides the capability of operating at duty cycles more than 0 5 Soft switching condition is independent fromthe input voltage and output load just like other ZVT converters This ZVT cell can be used for flyback converter too Theproposed flyback converter provides soft switching for both the auxiliary and main switches Also all the above mentionedbenefits attained for the forward converter are provided for the flyback converter The complete analysis of the proposedforward converter its operating principals and design considerations are discussed in this thesis Moreover to verify thetheoretical analysis the converter simulation results and practical results are presented Then the operating intervals of theproposed flyback converter is illustrated At the end the conclusions of this thesis and suggestions for future research areexplained Key Words Forward converter soft switching zero voltage transition ZVT

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