The Analyses of Hard- and Soft- Switching SiC Schottky- Buck Converter Performance

In this project two types ofbuck converters, hard switching and soft switching buck
converters are compared in term of power lossand reverse recovery current of diode
in DC applications. The test circuit used is dc to dc buck converter circuit. The main
switch ofcircuit is the IGBT and the same type ofIGBT is used for both techniques.
The diode used is fastswitching type Silicon Carbide Schottky (SiC) diode.
First semester theory research has been verified with simulations, which were
conducted in Cadence Pspice 14.2. The power loss waveforms of diode and IGBT
transistor were obtained. Using those power waveforms the energy loss of both
circuits were calculated.
Second semester, hard and soft switching choppercircuitswere constructed on PCB
(Printed Circuit Boards), so that simulation results can be compared with
experimentation results. All the PCB layouts were prepared in ARES IV. Powerloss
waveforms were obtained from digital oscilloscope.
The simulation and experimentation values are found to be quite close to one
another. It has found that hard switching chopper has more energy losses comparing
soft switching chopper. The main losses occur during SiC diode turn-off (caused by
reverse recovery current), IGBT transistor turn-on (caused by ICe current spike) and
the highest main loss is IGBT turn-off (caused by tailing time, tailing current).
Reducing the turn-off and turn-on switching losses of the IGBT would imply
decreasing of the total loss of the system. Thatcould be done by implementing zero
voltage switching across the IGBT transistor which would decrease IGBT turn-on
and turn-off losses.