Björn Ållebrand and Hans-Peter Nee Electrical Machines and Power Electronics
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Transcript of Björn Ållebrand and Hans-Peter Nee Electrical Machines and Power Electronics
Comparison of commutation transients of inverters with silicon carbide JFETs with and without
body diodes
Björn Ållebrand and Hans-Peter NeeElectrical Machines and Power Electronics
Department of Electrical EngineeringKTH
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.