Comparison of silicon and silicon carbide semiconductors for a 10 kV switching application

A simulation-based study is presented which compares silicon (Si) and silicon carbide (SiC) based solutions for a 10 kV switch, operating at frequencies of between 200 Hz and 2kHz in a hard-switched converter. Simplified device models, based on the ambipolar diffusion equation, are developed which allow comparison of p-i-n diodes and various IGBT structures in both Si and SiC. Optimised device parameters are determined which maximise the current carrying capability, subject to thermal dissipation limits, under specified switching conditions. A range of single switch and series switch combinations are examined and comparisons of electrical performance, cost and reliability made. The results show that the total losses for a 10 kV SiC switch and diode are just 17% of those of the equivalent Si devices. Furthermore, the SiC solution is shown to be cheaper, even after allowing for higher perunit area device costs. Although significant performance advantages can be obtained by utilising series combinations of Si devices, a single-device all-SiC solution displays just 36% of the total losses of a 4-device series connected Si solution when switched at 2 kHz. A study of interim solutions, employing Si switches and SiC diodes, shows that a series combination of 2.5 kV trench-IGBT devices and SiC p-i-n diodes offers the most cost-effective route to a high-performance 10 kV, 500 Hz switch.