Development of a new soft switched phase shifted full bridge PWM DC-DC converter

Full bridge isolated DC-DC converters are widely used in applications such as switch mode power supplies, high voltage power supplies, arc welding machines and battery chargers at high power and frequencies. In Full Bridge (FB) converters switching losses and the parasitic oscillations between leakage capacitance of power switches and transformer leakage inductance reach unacceptable values. In these applications it is required to decrease switching losses and current and voltage stresses of power switches with modern Soft Switching (SS) methods to increase efficiency and power density and to decrease EMI noise.In these converters MOSFET is mostly prefferred and by using Phase Shift (PS) method a Quasi Resonant (QR) is formed between the parasitic capacitance of power switches and transformer leakage inductance, so the leakages are utilised beneficially and SS is obtained. In this topology the energy in parasitic capacitance is discharged by using the energy in the leakage inductance. MOSFET is turned on with Zero Voltage Transition (ZVT) and turned off with Zero Voltage Switching (ZVS). In PS FB PWM DC-DC converters some problems arises such as variation of duty cycle with load current, hard switching because of insufficient energy in leakage inductance at light loads, and high voltage peaks and oscillations on the output diodes, and increment in the conduction losses because of the current flowing in the free wheeling interval. There are lots of studies on these converters and to solve the problems of these converters in the literature.In this thesis, a new PS FB PWM DC-DC converter is developed. In this converter IGBT is used and the problems listed above is solved and the converter will be applied to high power applications.