The investigation of soft switched DC-DC converters

Pulse width modulation (PWM) technique has been widely used in industry due to its high power density, fast transient response and ease of control. Operating frequency should be increased in order to obtain higher power density and faster transient response but in that case electromagnetic interference (EMI) and radio frequency interference (RFI) noises and switching losses in semi-conductor devices increase as well. In order to decrease these noises and losses, soft switching (SS) techniques should be used instead of hard switching (HS) techniques. This approach has been very popular in last years and continues to be so. In this thesis, DC-DC converters, control and soft switching techniques are investigated. Zero voltage transition PWM DC-DC converters are analyzed in detail. A new boost converter with an active snubber cell is proposed and compared with the other converters. The proposed converter provides zero voltage transition (ZVT) and zero current transition (ZCT) for the main switch. All of the semiconductor devices turn on and off under soft switching. The converter has a simple structure and minimum number of components. Steady state analysis of the converter is presented, and theoretical analysis is verified by a prototype of a 1 kW and 100 kHz boost converter. Keywords : DC-DC converter, soft switching, zero voltage transition, zero current transition.