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Silicon Carbide (SiC)

High junction temperature

Hans Bängtsson 2016-04-12

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Properties of Silicon Carbide

• High junction temperature

• Low losses, especially switch losses

• Parallel connection of components

• High voltage

Important properties of SiC in traction applications

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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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• 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

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Press pack

• Presspack

• Press-pack to fully utlize the temperature capability

cooler

cooler

Insulation

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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

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 voltageThe 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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Vo

lta

ge

(V

)

Current (A)

Si FET

500 400035002500200015001000

7000V

1000V

2000V

3000V

4000V

5000V

6000V

10 000V

9000V

8000V

Si IGBT modules

on AlSiC

SiC unipolar device

SiC Bipolar device

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

• 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

• Output power

• On state losses

• Switch losses

• Current sharing

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The LTH 12 kW inverter