An optimal switching pattern for SiC+Si hybrid device based Voltage Source Converters

In this paper, a new type of hybrid switching device with parallel connection of SiC and Si active switches, such as “SiC JFET + Si IGBTs” or “SiC MOSFET + Si IGBTs”, is introduced and applied to a 250kW back-to-back Voltage Source Converter (VSC). Considering the different switching speeds and output characteristics of SiC and Si devices in such hybrid structure, a novel optimal switching pattern is proposed to enable the Zero Voltage Switching (ZVS) for Si IGBTs. This proposed switching pattern optimally utilizes the better conduction characteristics and lower switching loss of SiC devices based on the instantaneous load current values, therefore significantly reduces the semiconductor losses in comparison to conventional all-Si VSCs. Simulations of back-to-back converters with different hybrid devices namely, “SiC JFET + Si IGBTs” and “SiC MOSFET + Si IGBTs”, are carried out in PLECS environment. Simulation results illustrate that the overall efficiency of back-to-back VSC can be improved by up to 4.8% if conventional Si devices are replaced with “SiC+Si” hybrid devices with the proposed switching pattern.