Silicon Carbide (SiC)
High junction temperature
Hans Bängtsson 2016-04-12
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Properties of Silicon Carbide
Important properties of SiC in traction applications
• High junction temperature
• Low losses, especially switch losses
• Parallel connection of components
• High voltage
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SiC components
Different kinds
• BJT Bipolar Junction Transistor
• JFET
• MOSFET
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Silicon Carbide Components
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BJT Bipolar Junction Transistor
• Low on-state voltage losses
• Current controlled –more complicated base drive unit
• High voltage capability
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JFET Field effect transistor
• Normally-on or normally-off
• Low on-state losses.
Normally-on has lower on-state losses than normally-off.
The normally-on losses are comparable to the BJT losses
• Voltage controlled –simple gate drive unit
• Gate drive units of Normally on components must always
have supply voltage, otherwise a short circuit
• Lower voltage capability than BJT
•Anti-parallell diode can be included in the JFET
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MOSFET
• Low on-state losses
• Voltage controlled – a simple gate drive unit
• Lower voltage capability than BJT
• (Anti-parallell diode is included in the transistor)
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High junction temperature
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Broad band semiconductor
Conduction band
SiC
Requires high temperature for
theraml ionisation
Valense band
Si
Conduction band
Doping level
Requires lower temperature for theraml ionisation
Doping level
Valense band
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High operating junction temperure
• Positive
• Reduced risk of component destruction due to too high junction
temperture
• Share cooling system with other apparatus which has less critical
temperature requirement
•Smaller heatexchanger due to higher temperature difference
• Negative
• Higher operating temperature, higher temperture swing
• Housing does not match the junction temperture capability
• Silicon Carbide has higher temperature expansion coefficient than
Silicon, bi-metal effect with substrate
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Press pack
• Presspack
• Press-pack to fully utlize the temperature capability
Insulation
cooler
cooler
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Shared cooling system with Combustion Motor
Ordinary silicon component with limited temperature capability.
The cooling liquid from the combustion motor is too hot to be
shared
Silicon equipped
motor inverter
Combustion Motor
Heat
exchanger
Heat
exchanger
SiC equipped
motor inverter
Combustion Motor
Heat
exchanger
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Low losses
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Low on state and switch losses
•Positive
• Remeber, Losses in base or gate drive units must
be included
• Negative
• Low switch losses is a result of fast switching, which
increases electro-magnetic interference (EMC)
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Study of SiC component properties
• A theoretical
study has been performed, in which the SiC
properies has been compared with Si components. Following
component combination have been studied
• Si IGBT - Si diode
• Si IGBT - SiC schottky diode
• SiC JFET – SiC schottky diode
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Test case, simulated dc-supplied system
AM
AM
MCM
AM
AM
The speed and effort of the train
together with line voltage
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The traction system
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Total losses in MCM and motor at
550 Hz switch frequency
Semiconductor
Losses
Si IGBT Si diode
100%
Si IGBT SiC diode
75%
SIC JFET SiC diode
25%
Comment
With SiC technology typical power loss reduction is 3-5 times
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Parallel connection of components
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Improved current raiting
Parallel connection of many component is possible due
to positive temperature coefficient (PTC).
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High voltage
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Increased voltage capability with SiC
10 000V
9000V
SiC Bipolar device
8000V
7000V
IGBT
Voltage (V)
6000V
5000V
4000V
3000V
SiC unipolar device
2000V
1000V
Si IGBT modules
on AlSiC
Si FET
500
1000
1500
2000
Current (A)
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2500
3500
4000
SiC at LTH
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SiC projects at LTH, Lund University
• Master thesis work. Theoretical modelling of
SiC components
• Master thesis work. A theoretical design of a
BAS inverter in a car (Belt driven Alternater
and Starter) ”light hybridasation”, 5 kW
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SiC projects at LTH, Lund University
• Doctoral student Luyu Wang together with
Getachew Darge have built a 12 kW three
phase inverter, with SiC bipolar junction
transistors and with SiC schottky diode.
The work includes design of the base drive
unit. Customer Bombardier Transportation AB
• Together with Fairchild TranSiC and QR-tech
Luyu Wang has designed and built a silicon
carbide based inverter for a hybrid car
electical drive system, with 80kW rating
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Design aspects of 12 kW 3-phase
inverter
• Three-phase 12 kVA VSI at 600 Vdc dclink voltage for
motor drive
• 10 kHz switching frequency
• 3 parallel transistors per position
BJT BT1206AC-01, 6 A, 1200V
Supplied by Fairchild TranSiC
• 2 parallel diodes per position
Diode IDH15S120, 15 A, 1200V
Supplied by Infineon
• Free convection (no fan)
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Study of the LTH SiC inverter
Measurement to verify important properties
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Output power
On state losses
Switch losses
Current sharing
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The LTH 12 kW inverter
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