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Comparison of commutation transients of inverters with silicon carbide JFETs with and without body diodes Björn Ållebrand and Hans-Peter Nee Electrical Machines and Power Electronics Department of Electrical Engineering KTH Background I • SiC has approximately ten times higher critical electric field compared to Si. • This makes SiC attractive for majority carrier (uni-polar) devices. • For bi-polar devices the large band gap will lead to high losses. • This means that a SiC IGBT will only be interesting for the highest voltage levels. Background II • There is problems with manufacturing SiC MOSFETs. • Therefore the interest has shifted to SiC JFETs. • There are different ways of designing SiC JFETs. • Buried gate JFETs and Vertical JFETs. Different SiC JFET designs Bg-JFET VJFET Inverter topology Commutation Procedure I Commutation Procedure II Simulations • Simulations show that it is not much difference between inverters using the different SiC JFETs. • The switching losses will be slightly larger for inverters with SiC JFETs without body diodes. Short-circuit current Large gate-drain capacitances Reducing short-circuit currents • Reducing the gate-drain capacitance (redesign of the component). • Increasing the gate voltage to a higher value (may lead to that the component must be redesigned). New Simulations • In simulations with the gate-drain capacitance lowered by a factor of two, the switching losses were reduced. Conclusions I • Using an inverter with only SiC JFETs is possible. • Using different SiC JFETs will not affect performance that much. • A drawback is that short-circuit currents will occur and this increases the switching losses. • The short-circuit currents can be reduced by different means. Conclusions II • The gate-drain capacitance has to be reduced. • Or a higher gate voltage needs to be used. Future Work • Investigate how the short-circuit current will be for larger devices. • How will the stray inductance affect this short-circuit current.