cooling igbt modules with vdf

Cooling of IGBT Modules with Vaporizable Dielectric Fluid (VDF)

David B. Levett and Jeremy C. HowesParker SSD Drives, Charlotte NC USA

David L. SaumsDS&A LLC, Amesbury MA USA

IMAPS France Advanced Technology Workshop on Thermal Management 2008, La Rochelle, France 30-31 January 2008

2 Levett, Howes, Saums – Cooling of IGBT Modules with Vaporizable Dielectric Fluid • IMAPS France ATW Thermal 2008 • La Rochelle, France

Outline and Goals

• Vaporizable dielectric fluid (VDF) concept:• Explain how a VDF-based cooling system operates; • Illustrate air-cooled heat sinks and liquid cold plate designs developed.

• Show comparative test results for three cooling solutions:• Traditional forced-air cooling (as used in production drive systems)• Water/ethylene glycol and traditional liquid cooling• VDF-based liquid cold plates and cooling system

• List positive and negative attributes of each system solution• Show test data to indicate VDF cooling system technical attributes.• Demonstrate a complete proof-of-concept 750kW/1000HP inverter design utilizing a

VDF cooling system.


A Brief History

• 1999: Thermal Form & Function LLC contracts with Compaq Computer Corporation to develop pumped liquid multiphase cooling (PLMC) system concept.

• 2004: TF&F demonstrates enterprise server cabinet PLMC system prototypes• 2005: Parker Hannifin acquires Eurotherm/SSD Drives.• 2007: Parker Hannifin Corporation and Thermal Form & Function LLC announce

collaboration to develop and patent vaporizable dielectric fluid (VDF) cooling system for high performance server processors:

• Highly constrained physical space availability within server cabinets• Highly constrained cost targets for commercial applications• Very high heat flux• Processor die power level: 400W.

• 2007: Parker Hannifin Corporation initiates joint development project to design production VDF-cooled drive system.

• Question: “Can VDF technology be scaled up to cool power semiconductor devices?”


A Brief History

• Drive system development partners:• Parker Hannifin Climate Systems Division (New Haven IN USA) – Component

development and manufacturing:Liquid cold platesSeparatorCondensorQuick-disconnectsFluid distributors

• Parker Hannifin SSD Division (Charlotte NC USA) – IGBT drive system development• Parker Hannifin Corporation – Pump design and development• Thermal Form & Function LLC (Manchester MA USA) – Liquid cold plate,

condensor, cooling system thermal analysis and component design

VDF: Vaporizable Dielectric Fluid


How does VDF cooling work?

VDF cooling loop with a pump, three cold plates and air cooled condenser.

Air Cooled CONDENSER

3 x cold plates

Pump

Vapor

Liquid


Key Points: VDF Cooling Loop

• Water system:• For water, 4.2J (0.00398 BTU) are required to raise the temperature of 1g (0.035 oz.)

of water by 1°C (1.8°F).• Therefore, to dissipate 1kW (3414 BTU/hr.) of power, a flow rate of 2.9 l/min. (46

gal./hr.) is required, assuming a 5°C increase in water temperature.• VDF system:

• Uses liquid-to-gas phase change of common refrigerant such as R134-A. • As long as there is fluid in the cold plate, the cold plate surface will be held close to

the boiling point of the fluid.• For 40°C refrigerant, 151J (0.143 BTU) are required to convert 1g (0.035 oz.) of

refrigerant from liquid to gas.• Therefore, to dissipate 1kW (3414 BTU/hr.) of power, a flow-rate of 0.35 l/min. (5.8

gal./hr.) is required.• Lower flow rates for VDF system equate to a smaller pump, power supply, reservoir, and

smaller tube diameters.


Key Points: VDF Cooling Loop

• VDF system:• Pressure and temperature are allowed to “float” relative to ambient conditions.

• System design target: System is designed for maximum power load at maximum ambient conditions.

• No compression cycle: System cannot cool below heat exchanger medium temperature. This is not refrigeration.

• Gravity fed: • Pump must be located below liquid cold plates in the loop.• Heat exchanger must be located above the liquid cold plates in the loop.

• Heat exchanger can be:• Air-to-fluid (i.e., traditional tube-and-fin);• Water-to-fluid (e.g., shell-and-tube for external chilled water or tower).

• System design engineer may set the refrigerant saturation temperature by adjusting system operating pressure:

• Adds additional degree of freedom for system design;• Higher pressure will increase saturation temperature, enabling a higher junction

temperature and smaller condenser and/or lower airflow.• Refrigerant or other dielectric vaporizable fluid will tolerate greater temperature

extremes for outdoor applications.• “Refrigerant agnostic”: Alternative refrigerants and dielectric fluids may be selected,

with some changes required in system component design.


Test Bed and Conditions

EconoDUAL™ is a trademark of Infineon Technologies

• IGBT Modules tested are dual 1700V, 450A in the 122mm x 62mm EconoDUAL™ package.

• Three modules are used in one mechanical assembly and can be configured as either:• Three-phase bridge• Single dual switch, operating in parallel.

• Functional modules for system testing:• Supplied as production modules but without internal protective gel;• Painted for improved emissivity;• Die temperatures measured with thermal camera.

• Maximum module load measured for each type of heat sink or cold plate to produce an IGBT junction temperature (TJ) of 120°C.

• Two test conditions selected:• 100% steady-state load;• Load condition with 220% 10-second overload capability.


Test Bed and Conditions

• Air-cooled heat sink operated at 40°C and 150CFM air flow.• All water-cooled liquid cold plates operated at:

• Water flow rate of 2 gal/min per cold plate;• Operated in parallel for a 6 gal/min total flow rate;• Maximum air temperature: 40°C;• Maximum temperature rise in heat exchanger: 10°C.

• VDF cold plates operated at:• Minimum flow rate of 0.4 gal/min per cold plate;• Operated in parallel for a 1.2 gal/min total flow rate;• Maximum air temperature: 40°C;• Maximum temperature rise in heat exchanger: 10°C.


Heat Sinks and Cold Plates Tested

• Case A – Air-cooled Heat Sink:• Extruded aluminum monolithic heat sink, traditional stock design;• 14:1 fin length to pitch ratio.

• Case B – Standard water-cooled liquid cold plate:• Extruded aluminum plate, traditional stock design;• Press-fit continuous copper tubing in back side of plate.

• Case C – Custom water-cooled liquid cold plate:• Machined aluminum plate;• Continuous copper D-shaped tubing epoxy-bonded into device mounting surface of

the plate;• Tubing circuit aligned with device die locations for maximum heat transfer.

• Case D – Custom water-cooled liquid cold plate:• Machined aluminum plate with machined cavity;• Aluminum offset convoluted fin brazed into machined cavity.

• Case E – Custom VDF cold plate:• Machined copper cold plate with machined cavity;• Copper offset convoluted fin brazed into machined cavity.


Three module assembly. Bus capacitors at top. Gel-less painted module on right. Copper tube bonded water cold plate fitted. (Liquid cold plates illustrated are Case C – Custom machined aluminum cold plate.)

Phase Module: 1200VAC 450A EconoDUAL


Open module showing DCB and die layout. Larger die are IGBT’s and smaller die diodes.

IGBT Internal View


Thermal image of module die operating at load

IGBT Thermal Image at Load


Die layout and equivalent thermal image

IGBT Die Layout


Aluminum extruded air-cooled heatsink

Case A: Air-Cooled Extruded Aluminum Heat Sink


Aluminum water-cooled plate with press-fitted copper tube inserts

Case B: Water-Cooled Continuous Copper Tube Aluminum Liquid Cold Plate


Aluminum water cold plate with inserted aluminum convoluted fin pack brazed into cavity

Case D: Water-cooled Custom Aluminum Convoluted Fin Liquid Cold Plate


Prototype single VDF copper cold plate with copper convoluted fin brazed into cavity. (Test cold plate shown has a thicker plate to allow for insertion of thermocouples.) IGBT module attached.

Case E: Prototype VDF Copper Offset Convoluted Fin/Copper Liquid Cold Plate


VDF Cold plate thermocouple locations under IGBT and diode die

Case E: Prototype VDF Liquid Cold Plate – Thermocouple Locations


VDF prototype cold plate with a clear cover and convoluted copper fin pack. (Note: Case E1 and E2 test data reflect straight fin pack.)

Case E: Prototype VDF Copper Convoluted Fin/Copper Cold Plate – Internal View

Convoluted copper fin pack for VDF cold plateused for test data for Case E1 and E2


Heat Sink/Cold Plate Performance Comparison Table

Table 1Module Loss (W)

for 120°C junction, Steady State

Module Loss (W) for 120°C junction, 220% overload

Heat Sink/Cold Plate Resistance+

°C /W

Equivalent rms output current* and ratio to air,

Steady State

Equivalent rms output current* and ratio to air,

220% overload

Case A: Air Cooled 600 405 0.094 194/1.0 120/1.0

Case B: Water-cooled Aluminum Cold Plate (Press-fit Standard Copper Tubing)

736 437 0.051 220/1.13 130/1.08

Case C: Water-Cooled Aluminum Cold Plate (Bonded Copper D-Shape Tubing)

1070 500 0.035 295/1.52 152/1.27

Case D: Water-Cooled Aluminum Cold Plate (Brazed Convoluted Fin, Machined Cavity)

1040 490 0.037 293/1.51 150/1.25

Case E1: VDF Copper Cold Plate(450A device)

1461 660 0.009 396/2.04 190/1.58


1184 568 0.008 330/1.7 164/1.37

+ Thermal resistance measured to heat sink base.* Equivalent rms current calculated at 60Hz output, switching at 2kHz with a 1000V DC bus.


Heat Sink/Cold Plate Performance Comparison: Additional Capacity Achieved


Cooling Loop Comparison Table

Table 2Fan/pump power to cool 1KW load (W)

Cost ratio of complete

cooling system, IGBT modules

Ratio of cooling system and IGBT

module cost per amp Steady State

Ratio of cooling system and IGBT

module cost per amp 220% overload

Heat Sink ΔT during 10s

600W Overload (°C)

Heat Sink ΔT under module Steady State

(°C)

Case A: Air Cooled 45 1.0 1.0 1.0 29 23

Case B: Water-cooled Aluminum Cold Plate (Press-fit Standard Copper Tubing)

295 1.3 0.87 0.83 18 18

Case C: Water-Cooled Aluminum Cold Plate (Bonded Copper D-Shape Tubing)

203 1.5 1.01 0.84 20 19

Case D: Water-Cooled Aluminum Cold Plate (Brazed Convoluted Fin, Machined Cavity)

209 1.7 0.94 0.74 19 23


12 1.3 1.57 1.22 5 6


15 0.95 1.79 1.44 5 4


Forced Air Cooling System

Pros• Low cost heatsinks and fans.• Large supplier base and range of options.• Air can cool other components such as bus bars,

electronic circuits.• Low maintenance.• Very broad design knowledge base.

Cons• Not very efficient for heat transfer.• Large volume of air requires ducting which can impose

constraints on mechanical layout and design.• Space inefficient.• Air can contain water/contamination. • Acoustical noise.• Performance is affected by altitude.


Water-based Cooling System

• Pros• Water is readily available.• Choice of liquid cold plate suppliers with

different price/performance ratios.• Small size and low weight of cold plates.• Heat exchanger can be placed remote to

heat source.


Water-based Cooling System

• Cons• Fluid leaks can cause serious damage and failure of equipment.• Water can be corrosive and has potential for biological contamination.• High flow rates require large pumps, power supply, pipe diameters and reservoir.• Protection required as a pressurized system. • If operated in series there is thermal stacking.• Potential for condensation.• Ethylene glycol is not environmentally friendly.


• Pros• Very good thermal performance/cost ratio.• Under cyclical load, reduced module baseplate ΔT.* • Low flow rates allow use of:

• Small, low-power pump• Small reservoir• Reduced-diameter tubing.

• Lower overall system weight.• Dielectric coolant reduces risk of short circuits or

damage in case of a leak.• Heat exchanger location can be remote from heat sources. • Low thermal stacking for liquid cold plates operated in series.• Allows use of simple quick-disconnect system for coolant loop.

VDF-Based Cooling System

* For module failure mode due to insulator-to-baseplate delamination, a 10°C reduction can increase life by a factor of three.


• Cons• Medium and pumps not as readily available. • Protection required as a pressurized system.• Very narrow design and application knowledge base.• Gravity feed requirement restricts large changes in operating orientation and places

limits on mechanical design and system layout.• R134A is a greenhouse gas.

VDF-Based Cooling System


750kW/1000hp Proof-of-Concept Inverter with VDF Cooling Loop and Air-based Heat Exchanger

• Inverter and heat exchanger built into a 500mm wide, 600mm deep and 2000mm tall enclosure.

• Five pluggable sections:• Pump module.• Three VDF-cooled inverter phases each with three 1700V 450A IGBT modules.• Additional capacitor module.

• 150mm long 50mm diameter pump. • Cooling loop designed for 10kW of losses from IGBT modules operating in 50°C

ambient air.


Capacitor module

Three invertermodules

Pump module

Vapor liquidseparator

Fluid to airheat

exchangerScroll fan for heat

exchanger

Front view of complete driveInternal view from back of drive

750kW/1000HP Proof-of-Concept Drive with 10kW VDF Cooling Loop


Exploded cold plate with fin pack

Pluggable coolantinlet connector

Pluggable coolantoutlet connector

IGBT module mountedon cold plate

Mechanical mounting frame

VDF Cooling Loop for Single Pluggable Phase Assembly


The Future

VDF cooling offers the design engineer another level of flexibility and performance but is not the solution for every application

Arenas which lend themselves to this technology:• Where weight and size are important.• Applications which experience high cyclical loads.• Applications using “live” heatsinks for example with puck style devices or for EMC

reduction. • Designs that require more power output from a given device package for example

increased switching frequency or difficulty in paralleling devices.• Systems with multiple loads in the cooling loop connected in series which also require

low thermal stacking.• Applications which already have a refrigerant loop.• Systems that require fast easy servicing and quick connect coolant connectors that can

be used alongside high voltage.


Mérci!


Contact Information:

Parker Hannifin Corporation Dale R. Thompson, Business Development ManagerClimate Systems Division E: [email protected] Rose Avenue www.microsystemscooling.comNew Haven IN 46774 USA

Parker SSD Drives Division Jeremy Howes, Senior Mechanical EngineerParker Hannifin Corporation E: [email protected] 9225 Forsyth Park DriveCharlotte NC 28273 USA David B. Levett PhD, R&D Engineer

E: [email protected]

DS&A LLC David L. Saums, Principal100 High Street E: [email protected] MA 01913 USA www.dsa-thermal.com


Appendix


Cross Section of a Complete Three-phase Inverter with a VDF Cooling System


Vaporizable Dielectric Fluids

• Available fluids:• Dupont DP-1• 3M EMMD Fluoroketones (FK) and Hydrofluoroethers (HFEs):

• Novec™• Solvay Galden™ • Others (including other refrigerants in HFC family)

• Certain vaporizable dielectric liquids address Greenhouse Gas (GHG) potential with values less than 1.0

• Selection of fluid for VDF systems requires consideration for system design:• Fluid heat capacity (as different from water)• Pump (type of pump, flow-through lubrication and selection of lubricants, and pump

sizing)• Condenser (sizing)• Tubing diameter

cooling igbt modules with vdf

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