High Current Ripple for Power Density and Efficiency Improvement in Wide Bandgap Transistor-Based Buck Converters

With the recent development and availability of wide bandgap devices in the market, more and more power converters are being designed with such devices. Given their fast commutation, when compared to their equivalent Si-based counterparts, these new devices allow increasing the converter's efficiency and/or power density. However, in order to fully avail these new devices, one should precisely know their switching characteristics and exploit it the best way possible. This paper recalls our own precise method to measure separately turn-on and turn-off energies of wide bandgap devices. This method is applied to commercially available SiC and GaN transistors and results show that they present much lower turn-off than turn-on energies. For that reason, we show that a SiC-based buck converter must have high current ripple in the output filter inductor in order to decrease transistor losses. Analysis of these losses as well as experimental results are presented. Finally, the precise design of a 2-kW SiC-based buck converter for aircraft applications is performed for different current ripples and switching frequencies. We show that current ripple higher than 250% of the dc load current significantly decreases the converter's losses, and consequently allows the increase of the switching frequency, which reduces the system volume and weight.