Abstract
The accurate prediction of the SiC MOSFET withstanding time for single fault events greatly influences the requirements for device protection circuits for these devices in power converter applications, like voltage source inverters or power electronic transformers. For this reason, a thermal model, based on the structural design and the physical dimensions of the chip as well as material properties of 4H-SiC, is proposed. This article gives a general description of the thermal behaviour of vertical SiC MOSFET under various driving and boundary conditions in case of a short-circuit event. The thermal model substitutes destructive tests of a device for an individual set of boundary conditions of an occurring fault event. The validity of the analytically parametrised thermal model is verified by experimental short-circuit tests of state-of-the-art vertical SiC MOSFETs for a set of various boundary conditions. The investigated thermal model can furthermore be used to standardise different gate-oxide degradation values from the literature for means of lifetime prediction of the gate oxide for an individual application under repetitive occurring fault or overload conditions. These manufacturer specific reported values measured with no standardised testing procedures can be translated into a maximum junction temperature, which is repeatedly reached. The thermal model therefore provides a unifying parameter for the gate-oxide lifetime calculation for an individual chip and application.
Highlights
Due to their superior material characteristics over silicon, like higher breakdown field strength, increased operating temperature, fast switching speed, and higher thermal conductivity, vertical SiC power MOSFETs are gaining more and more attention for use in voltage source inverters or electronic transformers for highly efficient, high frequency energy conversion in electric vehicles, trains, and more electric aircraft
It can be seen that the MOSFET fails at 6 μs whereas the IGBT can withstand a SC pulse at the same DC-link voltage for almost 20 μs, which is an extraordinary long time and much more than the 10 μs guaranteed by the manufacturer
The second major difference between the two devices is the desaturation limit which is a lot higher for the SiC MOSFET compared to the IGBT
Summary
Due to their superior material characteristics over silicon, like higher breakdown field strength, increased operating temperature, fast switching speed, and higher thermal conductivity, vertical SiC power MOSFETs are gaining more and more attention for use in voltage source inverters or electronic transformers for highly efficient, high frequency energy conversion in electric vehicles, trains, and more electric aircraft. These devices, packaged as discrete chips in a standard industrial housing or many in parallel in a power module, enable an increase in power density in converters compared to converters equipped with conventional IGBTs based on silicon [1]. Current and voltage, measured at the terminal of the devices during a short-circuit event
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