Design, analysis and implementation of a new soft switched DC-DC pwm converter

Pulse width modulated (PWM) DC?DC converters have been widely used in industry due to their high power density, fast transient response and ease of control. Higher power density and faster transient response can be achieved only by increasing switching frequency. But switching losses increase with switching frequency. For this reason, the switching frequency can be increased by using soft switching (SS) techniques instead of hard switching (HS). Generally SS techniques can be classified as zero voltage switching (ZVS), zero current switching (ZCS), zero voltage transition (ZVT) and zero current transition (ZCT) techniques. In resonant circuits SS is provide naturally and perfectly because voltage or current is zero at switching intervals. However in these circuits power density is low, generally frequency is not constant and there is no PWM capability. Combining the advantages of resonance and PWM techniques, ZVT and ZCT techniques, that have perfect SS and PWM capabilities, were developed by using a short time or partial resonance only during the switching processes. In principle, an auxiliary switch and a short time or partial resonance are used in both techniques. It is aimed to snub or zero the switching losses of the main switch during the turn on and turn off processes with the ZVT and ZCT techniques respectively. It is aimed to snub or zero the switching losses of the main switch, at the turn on process with ZVT technique, and at the turn off process with ZCT technique. In recent years some studies have been realized on combining the ZVT and ZCT techniques. In this thesis, a new snubber cell is developed in order to increase the power density and the efficiency in PWM converters and to decrease the EMI noise. The developed snubber cell provides main switch both to turn on with zero voltage transition (ZVT) and to turn off with zero current transition (ZCT). The converter incorporating this snubber cell can work in a wide range of line and load voltages and can operate with soft switching at high frequencies. Also, in this converter all semiconductor devices operates with soft switching. There is no additional voltage stress in main components and the stresses of the auxiliary components are low. Also, the new converter has a simple structure, low cost and ease of control. The operation principle and detailed steady state analysis of a new ZVT-ZCT-PWM boost converter circuit, in which the developed snubber cell is used, is presented. The presented theoretical analysis is verified exactly by a prototype of 100 kHz and 500 W converter. Also, the overall efficiency of the new converter reached a value of % 98.3 at nominal output power. Keywords: Soft switching, active snubber cell, zero voltage switching, zero current switching, zero voltage transition, zero current transition.