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Silicon Carbide (SiC)

High junction temperature

Hans Bängtsson 2013-05-08

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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 of Silicon Carbide components• BJT Bipolar Junction Transistor• JFET• MOSFET

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Silicon Carbide Components

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• Low on-state voltage losses

• Current controlled –more complicated base drive unit

• High voltage capability

BJT Bipolar Junction Transistor

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• 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

JFET Field effect transistor

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• Low on-state losses

• Voltage controlled – a simple gate drive unit

• Lower voltage capability than BJT

• (Anti-parallell diode is included in the transistor)

MOSFET

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High junction temperature

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Broad band semiconductor

Conduction band Doping level

Doping level Valense band

Si

Conduction band

Valense band

SiCRequires high temperature for

theraml ionisation

Requires lower temperature for theraml ionisation

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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

• Presspack• Press-pack to fully utlize the temperature capability

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Shared cooling system with Combustion MotorOrdinary silicon component with limited temperature capability. The cooling liquid from the combustion motor is too hot to be

shared

Combustion Motor

Heat exchanger

Silicon equipped motor inverter

Heat exchanger

Combustion Motor

Heat exchanger

SiC equipped motor inverter

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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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MCM

AM

AM

AM

AM

Test case, simulated dc-supplied system

The speed and effort of the train together with line voltage 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%

CommentWith SiC technology typical power loss reduction is 3-5 times

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Parallel connection of components

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Improved current raitingParallel connection of many component is possible due to positive temperature coefficient (PTC).

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High voltage

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Vol

tage

(V)

Increased voltage capability with SiC

IGBT

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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

• Doctor 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 is under construction

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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

• Output power• On state losses• Switch losses• Current sharing

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The LTH 12 kW inverter