Impact of forward recovery effects in different Si-IGBT technologies used in hybrid Si-IGBT, SiC-MOSFET based ANPC topology

Abstract

Three-level Active Neutral Point Clamped (ANPC) topology is being extensively researched with hybrid arrangement of Si-IGBTs and SiC MOSFETs, with the former switching at low fundamental frequency and the later at high switching frequency, due to its potential cost and performance benefits. Apart from long commutation loops in hybrid ANPC topology, bipolar behavior of the Si-IGBT intensifies the challenges in fast switching of the SiC MOSFETs. Forward recovery of relatively slow switching IGBTs and diodes tend to be insignificant when compared to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E_{on},\ E_{off}$</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$E_{rr}$</tex> losses in power converters. However, with the increase in switching speed (di/dt) in SiC MOSFETs, in this hybrid ANPC configuration, the impact of forward recovery losses can become highly significant. Although no switching losses are expected in static IGBTs, the phenomena of Forward Recovery Voltage (FRV) is observed leading to additional overlap losses at each switching instant. The FRV also adversely impacts the Reverse Bias Safe Operating Area (RBSOA) of the SiC MOSFETs. This paper experimentally investigates and compare the impact of such FRV phenomena in various commercially available Si-IGBT technologies. Finally, the FRV related losses are compared with the rest of the switching frequency losses for the tested device technologies in order to evaluate the system level impact of such hybrid use of Si-IGBTs with SiC MOSFETs in ANPC topology.