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Advanced Soft Switching Inverter for Reducing Switching and Power Losses

Dr. Jason Lailaijs@vt.edu

540-231-4741

Virginia Polytechnic Institute and State UniversityNational Institute of Standards and Technology

PowerexAzure Dynamics

Project Duration: FY08 to FY10

2008 DOE Merit Review

February 28, 2008

This presentation does not contain any proprietary or confidential information

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Outline

• Purpose of Work

• Problems

• Challenges/Barriers

• Approach

• Accomplishments

• Publications and Patents

• Plans for Next Fiscal Year

• Summary

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Purpose of Work

Develop advanced soft switching inverter for traction motor drives to support the following DOE targets

• 105°C coolant temperature – by designing the junction temperature <125°C

• 94% traction drive system efficiency – by designing the inverter efficiency >98%

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System and Component Level Cost Trade-off with Consideration of Thermal Management System

• Dual cooling loops – Need dual thermal management systems, penalty on

system level cost, size and weight

• Single cooling loop with 105°C coolant – Need to beef up silicon or use wide bandgap devices,

penalty on component level cost– Need to use high temperature bulk capacitors,

penalty on component level cost, size and weight

– Need to design circuit with high temperature rating, penalty on component level cost

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Possible Solutions with Single 105°C Coolant Loop

• Loss reduction by reducing switching frequency will result in high motor current ripple and associated loss thus reducing the entire drive efficiency.

• Loss reduction by increasing device switching speedwill result in high dv/dt, di/dt and associated EMI and common mode current issues.

• Emerging SiC and wide band-gap devices for high temperature operation is not cost effective today.

• Junction temperature reduction by reducing thermal impedance – it helps but not enough.

• Advanced soft switching with silicon devices to achieve significant loss reduction – a cost-effective way.

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Challenges/Barriers

• High temperature operation– Need ultra high efficiency design for low voltage high

current – Need ultra low thermal impedance package – Need high temperature capacitors – Need high temperature circuit components (opto

coupler is a major problematic component)• Integration for cost reduction

– Need soft switch module for low cost production– Need to integrate high temperature gate drivers– Need to integrate low EMI auxiliary power supply– Need to integrate current sensor and conditioning

circuits

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Approach

• Develop a variable timing controlled soft-switchinginverter for loss reduction.

• Develop low thermal impedance module withintegrated heat sink for high temperature operation.

• Develop a highly integrated soft-switch module for low cost inverter packaging.

• Modeling and simulation for design optimization. • Test the soft-switching inverter with existing EV platform

and dynamometer for EMI and efficiency performanceverification.

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Technical Approach for FY08

• Obtain inverter component V-I stresses through motor drive simulation

• Predict device junction temperature through modeling and simulation

• Design variable timing control circuit • Design and fabricate high temperature soft switch

module for integration • Develop high-accuracy ratio metric calorimeter for

ultra high efficiency inverter/dyno testing• Test electromagnetic interference (EMI) performance• Test and validate module level thermal performance• Test and validate Inverter level thermal performance

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Timeline for FY08

2007Oct Nov Dec

2008Jan Feb Mar Apr May Jun Jul Aug Sep

Motor drive simulation

Dynamometer testing

Design report

Characterize and predict temperature rise

Decision point discussion: • Soft-switching inverter efficiency >98% • Low module thermal impedance ensures junction

temperature < 125°C under 105° heat sink condition

Test report

report

Design soft-switching circuits

Soft switch module fabrication/test

EMI testing Report

Test report

report

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Accomplishment – US 06 Vehicle Simulation

0 100 200 300 400 500 600-10

0

10

20

30

40

50

60

70

80

90Vehicle Speed

Drive Cycle SpeedVehicle Speed

0 100 200 300 400 500 600-8

-6

-4

-2

0

2

4

6

8x 104 Power

Inverter inputShaft outputMotor Input

100 400 600300 500200

Inverter output

9080706050403020100

-10Veh

icle

Spe

ed (m

ph)

806040200

-20-40-60-80

Pow

er (k

W)

Shaft output

Time (s)0

• Simulation results show inverter power level, voltage and current stresses

• In a typical driving cycle, vehicle runs below 20 kW most of time.

• Low-power efficiency is crucial to overall drive cycle efficiency

• Inverter peak power reaches 60 kW

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Accomplishment – IGBT Characterization Under Hard-Switching Condition

• Switching speed is significantly lowered under high temperatures• Device switching loss increases by 40% at 100°C condition

-1000

100200300400500

6.8 7.0 7.2 7.4 7.6 7.8-100

0100200300400500

2.6 2.8 3.0 3.2 3.4 3.6

ICVCE

101520253035

6.8 7.0 7.2 7.4 7.6 7.8

Eoff_100°C=17.9mJ

Eoff_25°C=12.4mJ0369

1215

2.6 2.8 3.0 3.2 3.4 3.6

Eon_100°C=9.7mJEon_25°C=7.0mJ

100°C

IC VCE

25°C

(b) Turn-offµs

(a) Turn-on

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Accomplishment – IGBT Characterization Under Soft-Switching Condition

• During turn-on, current IC rises after voltage VCE drops to zero• During turn-off, VCE slowly rises after IC drops to zero• Variable timing achieves soft-switching at all current conditions• Bonus – slow dv/dt that will result in low EMI emission

-1000

100200300400

14.0 14.2 14.4 14.6 14.8 15.0-100

0100200300400

1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

IC

VCEIC

VCE

-1000

100200300400

15.0 15.2 15.4 15.6 15.8 16.0

IC VCE

at 150A

(b) Turn-offµs

-1000

100200300400

2.2 2.7 3.2 3.7 4.2 4.7 5.2 5.7

ICVCE

(a) Turn-on

at 250A

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Accomplishment – Measured Device Switching Energy Under Different Operating Conditions

• As compared to 25°C operating condition,– Device switching loss is increased by 40% at 100°C – Device switching loss is reduced by 80% under soft switching

• Losses in soft switching are due to layout parasitics with discrete components – necessary to integrate the soft switch module

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1015202530

0 50 100 150 200 250 300 350 400

Eoff at 100°C

Eon at 25°CEon at 100°C

Eoff

Eoff at 25°C

Eon

Current (A)

Sw

itchi

ng e

nerg

y (m

J) IGBT rating = 600 V, 400 A Vdc = 300 V

soft switching

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Accomplishment – Half H-Bridge Power Module Chip Layout

Single Phase-leg Soft Switch Power Module

Upper Switch

Lower Switch

Output Section

Resonant Switching Section

IGBT

Free-Wheel Diode Liquid

Cooled Baseplate

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Accomplishment – 3-D Thermal Simulation Results for Temperature PredictionEach die loaded with power dissipations obtained from

circuit simulations

Output IGBT ΔT = 15 °C above bottom of baseplate

Cross section through IGBT & FWD

IGBT Die

Solder

Copper

Solder

Aluminum NitrideCeramic

Copper

Finned Baseplate/Heatsink

Cooling Medium

Heat Flow

Heat Flow Path

Pin fin base

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Accomplishment – Soft-Switching Inverter Simulation Results

96.0

96.5

97.0

97.5

98.0

98.5

99.0

0 5 10 15 20 25 30 35 40 45 50 55

Motor output (kW)

Pro

ject

ed e

ffici

ency

(%)

Hard switching

Soft switching

Inverter condition: Input 325V, switching at 20-kHz

• Use actual device model in simulation.

• New soft-switching design significantly improves low-power efficiency

• Over 50% loss reduction in low-power region

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Accomplishment – Development of Ratio Metric Calorimeter for Ultra High Efficiency Measurement

- Measure electric power out over power in results in poor efficiency accuracy at this power and efficiency level

- Calorimeter gives accurate power loss- Provides method to control temperature of coolant

midout

inmidheaterlossInverter TT

TTPP−−

=_

Thermal InsulationCalorimeter Ref. ChamberCalorimeter Main Chamber

Tin

FlowCoolantStorageReservoir

V

Pheater

ImmersionElectric Heater(s)

85-105°CcoolantTmid

divi

ding

wal

ldi

vidi

ng w

allFlow

ToutFlow

Inverter under test Liquid cooled

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Publications/Patents

• 1 technical paper under preparation– High temperature hard- and soft-switching device

characterization

• 3 invention disclosures under preparation– variable timing circuit for soft switching– new soft switch– new soft-switching inverter

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Activities for Next Fiscal Year

• Variable Timing Soft-Switching Inverter Demonstration

• Thermal Characterization of Gen-1 Soft-Switch Module

• Gen-2 Soft-Switch Module Design Optimization • Package 9 Soft-Switch

Phase-Leg Modules• Package 2 Gen-2 Soft-

Switching Inverters

Preparation for In-Vehicle Testing

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Summary

• Potential for petroleum displacement – Advanced soft-switching inverter for significant loss reduction, and

thus 105°C operation is possible for system level cost reduction and reliability improvement

• Approach to research– Modeling and simulation to predict the device requirement, junction

temperature, and inverter efficiency – Design of a novel soft switch module and a low-cost variable timing

control to achieve soft switching over a wide range • Technical accomplishments and timeliness thereof

– Completed most simulations, circuit design for variable timing control, and high-accuracy dyno test setup

• Technology transfer – 3 invention disclosures and 1 technical paper under preparation

• Plans for next fiscal year– Demonstrate high-efficiency inverter drive with the proposed design

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