Design and performance evaluation of SiC based DC-DC converters for PV applications

A performance comparison of SiC MOSFETs and JFETs in a high-power (1kW) DC-DC converter to form part of a single phase PV inverter system is presented. The drive design requirements for optimum performance in the energy conversion system are also detailed. The converter which is based on 1.2 kV 20A SiC switches and 600 V 8A SiC diodes was tested under continuous conduction mode at frequencies up to 250 kHz. The converter power efficiency, switch power loss and temperature measurements are then compared with the ultra high speed CoolMOS switches and SiC diodes. The high voltage, high frequency and high temperature operation capability of the SiC DUTs are also demonstrated. Increasing the frequency from 100 kHz to 250 kHz resulted in case temperatures of up to 191°C and an observed decrease in efficiency from 95% to 92.5% for the CoolMOS. The all SiC converters showed more stable efficiencies of 95.5% and 96% for the switching frequency range for the SiC MOSFET and JFET, respectively. A comparison of radiated noise showed the highest noise signature for the SiC JFET and lowest for the SiC MOSFET. The negative gate voltage requirement of the SiC MOSFET introduces up to 6 dBμV increase in radiated noise, due to the induced current in the high frequency resonant stray loop in the gate drive negative power plane.