NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Power Electronics Thermal 

Management R&D

Scot Waye

Organization: National Renewable Energy Laboratory

Email: Scot.Waye@nrel.gov

Phone: (303) 275-4454

Team members/collaborators: 

Gilbert Moreno (NREL), Madhu Chinthavali (ORNL)

DOE Vehicle Technologies Office

Electric Drive Technologies

FY15 Kickoff Meeting

Oak Ridge National Laboratory

Oak Ridge, Tennessee

November 18 –20, 2014 This presentation does not contain any 

proprietary or confidential information.

NREL/PR-5400-63002
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Thermal Management to Enable High-Temperature 

Power Electronics Based on Wide-Bandgap Devices

DOE APEEM FY15 Kickoff Meeting

State of the Art (SOA)

2013 Toyota Camry Hybrid inverter 

(also 2008 Lexus LS 600H)

• Double-sided cooling

• Compact size

Delphi Prototype (mid-2015)

• Meets DOE 2015 targets

• Low-loss semiconductors, thermal 

stack-up and materials, hightemperature capacitor, and inverterlevel packaging concepts, 105°C 

coolant
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Proposed Technology 

Strategy to Address Limitations of SOA

DOE APEEM FY15 Kickoff Meeting

System-level thermal 

management for 

inverter/converter 

components for scales 

from device to module to 

system

Limitations Addressed

• Device- to system-level 

thermal management 

and overall cooling 

strategies for high- temperature power 

electronic systems

Wide-bandgap (WBG): Silicon Carbide (SiC) / 

Gallium Nitride (GaN)

High-Temperature Silicon (Trench)

Silicon

Maximum Junction Temperature [°C]
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Challenges/Barriers to Meet Project Goals

DOE APEEM FY15 Kickoff Meeting

Program

• Acceptance of novel cooling technologies

o New technology needs to be placed in context similar to 

current SOA and shown how it replaces current system 

within packaging constraints

• Simulation useful for down-selection and 

comparison of technologies, but demonstration/ 

validation key to proving merit

• Cost of flow/heat transfer enhancements must be 

considered
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Challenges/Barriers to Meet Project Goals

DOE APEEM FY15 Kickoff Meeting

Technical

• Access to state-of-the-art designs

o Input from laboratory and industry collaborators providing 

computer-aided design of intellectual property protected 

systems (inverters, converters, chargers) allows for best 

analysis of current technologies

• Identifying acceptable packaging and thermal interface 

concepts to remove heat from capacitors, interconnects, 

control boards

• Some potential technologies or manufacturing 

techniques are in early stages of development and 

characterization (e.g., microchannels, three-dimensional 

printing, integrated casting)
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Project Approach

DOE APEEM FY15 Kickoff Meeting

• NREL for the last several years has focused on 

device- and module-level cooling strategies

o Single-phase liquid

o Air cooling

o Passive two-phase cooling
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• WBG devices (SiC, GaN) promise to increase 

efficiency, but also are challenging for thermal 

management

o Higher junction temperatures

o Decreased area (due to higher efficiency and desirable for 

lower cost [smaller or fewer devices]

Project Approach

DOE APEEM FY15 Kickoff Meeting

Si

WBG

Less efficient = More heat

Lower junction temperature

More efficient = Less heat

Higher junction temperature

Area can be >75% less → increased heat fluxes
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Thermal interface 

material (TIM) = grease

Device

Module

Electrical Interconnects

Capacitor

Control Board

2012 Nissan 

Leaf Inverter

Higher power levels produce thermal 

pathways into undesirable locations

Project Approach

DOE APEEM FY15 Kickoff Meeting
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Project Approach

DOE APEEM FY15 Kickoff Meeting

• Active cooling of components needed

o Devices

o Power modules

o Electrical interconnects

o Capacitors

o Other temperature critical components (e.g., control board)

• Some cooling strategies not compatible with targets

o High-temperature single-phase liquid coolant desirable to reduce costs

o 140°C under-hood temperatures

o 85°C capacitor must be kept cool

• TIMs between components need to have low thermal 

resistance to increase thermal performance and also be 

reliable at functional temperatures
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Project Approach – Overall

DOE APEEM FY15 Kickoff Meeting

Simulate inverter components from device- to system-level

Examine WBG-based inverter/converter thermal management cooling strategies 

from device- to system-level

Design, fabricate, and test prototype concepts

Create prototype for relevant thermal management locations. Conduct 

experiments to examine where the concept can be improved

Refine prototype and demonstrate concept(s)

Show technology meeting technical targets or pathway to meet targets through 

refined prototype design, fabrication, and testing
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Project Approach – FY15

DOE APEEM FY15 Kickoff Meeting

Define system-level inverter/converter

Define target application baseline system (with Oak 

Ridge National Laboratory [ORNL] input) with thermal 

specifications and constraints

Select simulation (modeling) approach

Simulate thermal management for system

Generate WBG-based inverter/converter thermal 

management concepts using device- , module-, and 

system-level simulated cooling strategies

Select and Report

Down-select 1–3 best cooling/packaging approaches

Report results
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FY15 Tasks to Achieve Key Deliverable

DOE APEEM FY15 Kickoff Meeting

2014

Oct Nov Dec

2015

Jan Feb Mar Apr May Jun Jul Aug Sep

Go / No-Go Decision Point: If there are concepts that meet 2020 targets, proceed to 

designing prototype

Key Deliverable: Summary report (incorporated into annual report) providing comparison 

of packaging concepts and cooling strategy thermal performance

Define inverter/converter 

thermal specifications

Go/

No-Go 

Decision 

Point

Key 

Deliverable: 

Summary

Report

Select modeling approach for power 

electronics system-level thermal analysis

Simulate initial device-, modulelevel cooling strategies

Generate PE system-level thermal management 

concepts for WBG-based inverters/converters

Optimize module-level 

cooling strategies

Support ORNL power electronics R&D with thermal management for inverter/converter/ 

charger projects
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Specification Development

Thermal Specifications and Constraints:

Temperature limits

Heat generation from device losses

Thermal interface materials

Packaging constraints

Industry 

Input

Literature Experience

DOE APEEM FY15 Kickoff Meeting
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Technology Evaluation

Time scale

Software

Simulation 

Approach Modeling

Finite Element 

Analysis (FEA)

Steady state Transient

Computational 

Fluid Dynamics 

(CFD)

DOE APEEM FY15 Kickoff Meeting
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Multi-scale Analysis

Thermal Management Strategies

Device

• Die/substrateintegrated thermal 

management

• Microchannels

Module

• Enhanced surfaces

• Turbulence promoters

System

• Advanced 

manufacturing

• Multiple mode cooling

Han et al., 2000, Gas Turbine Heat Transfer and Cooling Technology

DOE APEEM FY15 Kickoff Meeting
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FY15 Tasks in Depth

1. Define target application baseline system from experience, literature survey, ORNL, 

and industry input for thermal specifications and constraints specific to WBG-based 

inverter/converter

2. Select the modeling (simulation) approach to be used for power electronic systemlevel analysis (e.g.– FEA, CFD, steady-state, transient)

3. Simulate initial device-, module-level cooling strategies

4. Generate power electronics system-level thermal management concepts for WBGbased inverters/converters

5. Optimize device-level cooling strategies

6. Down-select 1–3 best cooling/packaging approaches for application

7. Prepare a summary report and publish findings that include a comparison of current 

and proposed strategies

Support ORNL power electronics R&D in thermal management for 

inverter/converter/charger development

DOE APEEM FY15 Kickoff Meeting
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FY16 Tasks to Achieve Key Deliverable

DOE APEEM FY15 Kickoff Meeting

2015

Oct Nov Dec

2016

Jan Feb Mar Apr May Jun Jul Aug Sep

Go / No-Go Decision Point: If there are shortcomings in thermal 

management or size and weight can be 

improved from testing, proceed to refine 

prototype

Key Deliverable: Publish results of thermal performance testing

Design prototype 

components to be tested

Go/

No-Go 

Decision 

Point

Key 

Deliverable: 

Summary

Report

Design and build test bench 

(modifications for specific test)

Fabricate prototype Test prototype
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Transmission 

Fluid Loop

WEG Loop Air Test Bench

FY16 Task Description

• Fabricate prototype

• Modify or build test bench

• Test and optimize prototype

• Validate model and optimize

WEG = water-ethylene glycol
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FY17 Tasks to Achieve Key Deliverable

DOE APEEM FY15 Kickoff Meeting

2016

Oct Nov Dec

2017

Jan Feb Mar Apr May Jun Jul Aug Sep

Go/No-Go Decision Point: Outline any targets not met and outline pathway 

to reach them (light-weighting, size reduction, 

lower material and manufacturing costs)

Key Deliverable: Demonstrate system meeting technical targets. 

Publish results.

Refine prototype 

components and systems

Go/

No-Go 

Decision 

Point

Key 

Deliverable: 

Summary

Report

Modify test bench for additional 

testing and demonstration

Fabricate new prototype 

components and systems Test prototype
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Project Summary

DOE APEEM FY15 Kickoff Meeting

Project Duration: FY15 – FY17

Overall Objective (all years): Provide thermal management solutions 

for WBG-based (and high-temperature Si) power electronics systems 

FY15 Focus: Define thermal specifications for inverter components, simulate baseline and proposed 

cooling strategies, down-select most promising concepts

Deliverable: Summary report providing comparison of packaging concepts and cooling strategy thermal 

performance.

Go/No-Go Decision Point: Down selection of packaging concept with cooling strategy that meets 2020 targets 

and beyond.

FY16 Focus: Design, fabricate, and test prototype packaging concept with cooling strategy

Deliverable: Publish results of thermal performance testing.

Go/No-Go Decision Point: If there are shortcomings in thermal management or size and weight can be improved, 

proceed to refine prototype.

FY17 Focus: Refine and update prototype to increase thermal performance, size, and weight, balancing 

fabrication process (cost) with thermal performance

Deliverable: Demonstrate system meeting or exceeding technical targets. Publish results.

Go/No-Go Decision Point: Outline any targets not met and outline pathway to reach them
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Technology-to-Market Plan

DOE APEEM FY15 Kickoff Meeting

• Support ORNL 55-kW inverter and ORNL 6.6-kW isolation 

converter development

• The concepts generated for thermal management will provide 

guidance to industry on potential solutions for active cooling 

of electrical interconnects

• Collaborations with industry will provide timely input on 

impactful technology implementation of thermal interface 

materials and cooling strategies for inverter/converter 

development
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Partners/Collaborators

DOE APEEM FY15 Kickoff Meeting

Organization Role

APEI Industry input on packaging and thermal 

management challenges

John Deere 

Electronic Solutions

Industry technical challenge input and test

platform

Oak Ridge National 

Laboratory

PE R&D (inverter/converter/ charger projects) –

NREL will provide thermal management support

PowerAmerica 

(WBG Institute)

Collaborations and interactions with Institute

members on thermal management challenges

Actively pursuing additional industry partners (OEM, Tier 1/2 suppliers) 

interested in providing technical input or collaborations.
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Capabilities

DOE APEEM FY15 Kickoff Meeting

• NREL Core Competency: Thermal management and 

reliability for power electronics

• High-performance computing cluster for CFD, 

thermomechanical FEA – parallel computing licenses from 

ANSYS

• Test benches: liquid (WEG) loop, air cooling, air balance-ofsystems, transmission oil loop, two-phase loop

• Thermal resistance characterization (ASTM TIM stand, 

xenon flash, high potential tester, transient thermal tester, 

acoustic microscopy, laser profilometer, sample synthesis)

• DC power supplies (various voltages, current)s
For more information, contact:

Principal Investigator

Scot Waye

Scot.Waye@nrel.gov

Phone: (303)-275-4454

APEEM Task Leader

Sreekant Narumanchi

Sreekant.Narumanchi@nrel.gov 

Phone: (303)-275-4062

Acknowledgments:

• Susan Rogers & Steven Boyd 

U.S. Department of Energy

Team Members:

Gilbert Moreno 

Madhu Chinthavali (ORNL)