Efficiency Improvement of Boost Converter for Fuel Cell Bus by Silicon Carbide Diodes 2016-01-1234

The adoption of silicon carbide (SiC) power semiconductors is regarded as a promising means of improving the fuel efficiency of all types of electrically powered vehicles, including plug-in, electric, fuel cell, and hybrid vehicles (PHVs, EVs, FCVs, and HVs). For this reason, adoption in a wide variety of vehicles is currently being studied, including in the fuel cell (FC) boost converter of an FC bus. The FC boost converter controls the output voltage of the FC up to 650 V. In this research, SiC Schottky barrier diodes (SiC-SBDs) were adopted in the upper arm of an FC boost converter. Since the forward voltage (Vf) of SiC-SBDs is smaller than conventional Si-PiN diodes (Si-PiNDs), the conduction loss of SiC-SBDs is correspondingly smaller. Recovery loss can also be reduced by at least 90% compared to Si-PiNDs since the recovery current of SiC-SBDs is substantially smaller. Lowering the recovery current of the upper arm has the effect of reducing the superimposed current when the silicon insulated gate bipolar transistors (Si-IGBTs) in the lower arm turn on. As a result, the turn-on loss of the lower arm can be reduced by approximately 70%. It was confirmed that installing SiC-SBDs in the upper arm of the FC boost converter improved efficiency by 0.5% in the load range over 50%.