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Thermal Management andPackaging of High TemperatureAutomotive Power ElectronicsGilbert Moreno3D Power Electronics Integration and ManufacturingJune 26, 2018This presentation does not contain any proprietary, confidential, or otherwise restricted information.Outline Motivation and objectives Describe the cooling systems currently used inautomotive power electronics Discuss current research: cooling the powerelectronics using dielectric fluids Future workNREL 2

Motivation Increase the market penetration of electric-drive vehicles(EDV)––––Hybrid electricPlug-in hybrid electricBattery electricFuel-cell electric vehicles Requires reducing the cost and increasing power density ofthe electric traction drive systemPower Electronics Targets (100 kW peak power)YearOn-road2025Cost [ /kW]*102.7Power density [kW/L]*18100*Source: Electrical and Electronics Technical Team Roadmap, October 1/f39/EETT%20Roadmap%2010-27-17.pdfNREL 3NREL 4Wide-bandgap Technology (WBG)WBG (silicon carbide, gallium nitride, gallium oxide)Benefits: More efficient Higher temperatures Higher voltages Higher switching frequenciesChallenges: Higher heat flux Higher cost High device temperatures presents packaging issues

ObjectiveDevelop thermal management techniques to enableachieving the DOE power density target of 100 kW/L Challenge is to create a thermal solution that allows forpackaging high temperature (250 C) wide-bandgap (WBG)devices next to capacitors that typically cannot exceed85 CNREL 5Current Automotive Power ElectronicsCooling Strategies Use water-ethylene glycol (WEG) in channel-flow type heatexchangers Require a dedicated, low-temperature WEG cooling system for thepower electronics and motor In most cases, the distance between components is large such thatthe capacitors and electrical boards do not require any cooling432 cm25cm2012 Nissan LEAF cold plate2012 Nissan LEAF power electronicsNREL 6

Automotive Power Electronics Cooling Trendcold plate cooledbase plate cooleddouble-side cooledIGBTIGBTceramic substrateceramic substratebase platebase plate / cold platecold plateIGBTthermalgreaseceramic substratecold plateNote: the automotive modules below may be slightly different from the above schematicsImage credit Gilbert Moreno(NREL)2012 Nissan LEAF2014 Honda Accord Hybrid2012 Camry Hybrid(2016 Prius is similar)NREL 7NREL 8Automotive Power Electronics Cooling Trend150R"th, junction to coolant on7550250cold plate cooled:2012 Nissan LEAFbase plate cooled:2014 Honda Accorddouble side cooled:2008 Lexus Hybrid(similar to 2016 Prius)Cooling configuration

Defining a Thermal TargetDefine thethermal targetrequired toachieve 100 kW/LComponentCompare potentialcooling strategiesDesign the coolingsystem via modelingVolume used for 100 kW/Linverter estimate [L]SourceGate driver (includes currentsensors)0.282015 BMWi3 (125 kW)Control board0.232012 Nissan LEAF (80 kW)Capacitor0.252015 BMWi3 (125 kW): Assumption: capacitorvolume decreased by 50% to account for a decrease incapacitor requirements for WBG devicesRemaining volume for powermodule and cold plate0.24Toyota Engineer Speaks on Advantages, Disadvantages of Silicon Carbide (SiC) Power Devices“ if switching frequency is improved by eight times by replacing a Si power device with a SiC power device, thevolumes of capacitors and reactors can be reduced by 70-80%. ”http://tech.nikkeibp.co.jp/dm/english/NEWS EN/20120207/204483/NREL 9Defining a Thermal TargetDefine thethermal targetrequired toachieve 100 kW/LComponentCompare potentialcooling strategiesDesign the coolingsystem via modelingVolume used for 100 kW/Linverter estimate [L]SourceGate driver (includes currentsensors)0.282015 BMWi3 (125 kW)Control board0.232012 Nissan LEAF (80 kW)Capacitor0.252015 BMWi3 (125 kW): Assumption: capacitorvolume decreased by 50% to account for a decrease incapacitor requirements for WBG devicesRemaining volume for powermodule and cold plate0.24 Heat dissipation requirements: 2,150 W (assuming 100 kW system, 98% WBG inverterefficiency, and 95% motor efficiency) Assuming Tj, maximum 250 C and T coolant 65 C, volumetric thermal resistance target is 21cm3-K/WNREL 10

Defining a Thermal TargetDefine the thermaltarget required toachieve 100 kW/LCompare potentialcooling strategiesSpecific thermal resistance R'' j-c (mm2·K/W)10,000DBC cooledbaseplate cooleddevice cooled1,000Device cooling Provides the lowest thermal resistance Enables cooling the electrical leads (decreasecapacitors and board temperatures)Electrical leads inthe 2015 BMWi3power module100Device101Design the coolingsystem via modelingDBCBaseplate100DBC: direct bond copper1,00010,000Heat transfer coefficient (W/m2·K)Image credit: Xuhui Feng (NREL)100,000NREL 11Defining a Thermal TargetDefine the thermaltarget required toachieve 100 kW/LCompare potentialcooling strategiesDielectric fluidElectrical leadElectrical conductorMOSFETElectrical conductorInexpensive dielectric materialDielectric cooling of planar packageDesign the coolingsystem viamodeling Propose a single-phase cooling approachü Easier to seal (compared to two-phasesystem)ü Potential to use automatic transmissionfluid (ATF) (decrease cost)x Low heat transfer. Propose to use jetimpingement to improve performance Cool the electrical interconnects Replace expensive ceramic dielectric materialwith cost-effective alternativesMOSFET: metal–oxide–semiconductor field-effect transistorNREL 12

Dielectric Coolant Selection Selected synthetic hydrocarbons that are used in electronics cooling(single-phase) applications– ElectroCool EC-140: Engineered Fluids (used this fluid for the thermal analysis)– Alpha 6: DSI Ventures (other possible option) Ultimate goal is to develop a system that uses ATF as the dielectricto decrease cost, use fluid already qualified for automotive use,enable motor – inverter integrationElectroCool EC-140 properties at 70 C temperature (used for thermal modeling)Thermal conductivity[W/m-K]Specific heat[J/kg-K]Density[kg/m3]Viscosity[Pa-s]Flash point[ C]Pour point[ C]0.162,3007970.017280-52Water/ethylene glycol (50 /50) properties at 70 C (provided for comparison)Thermal conductivity [W/m-K]Specific heat [J/kg-K] Density [kg/m3]0.423,494Viscosity [Pa-s]1,0380.00126NREL 13NREL 14CFD Jet Impingement Model DescriptionSlot jet model (sectional view)Fluids spreader widthw slot widthSlot jet inlet5 mmnozzle-to-surface distance:3 mmCopper metallizationFiller materialCopper metallizationSiC MOSFET (5 5 0.18 mm)Circular jet model (sectional view)Fluids spreader widthSiC MOSFET (5 5 0.18 mm)outletcircular jet inlet (d jet diameter)nozzle-to-surface distance:3 mmCopper metallizationFiller materialCopper metallization Evaluated effect of jet velocity ( 1 m/s maximum), heat spreader size, nozzlecharacteristic length (w, d) Tinlet 65 C, used laminar flow since Reynolds numbers 300CFD: computational fluid dynamics

Circular Versus Slot Jet Performance Comparison35 circular jet slot jetPredict circular and slot jetto have similar performancefor w, d 3 mm Best performance yields adismal thermal resistance of4.7 K/W. Would require 60devices to dissipate 2.2 kW Need to improve thermalperformance. Evaluatedusing finned surface toimprove performance.white symbols: w, d 1 mmblack symbols: w, d 3 mm30Thermal resistance, j-c [K/W] 252015105spreader width (s) 10 mm01.E-061.E-051.E-041.E-031.E-02Pumping power [W]NRELSubscripts j-c: junction-to-coolant 15Finned Heat Spreader Conceptside views1-mm-tallfinstop view5 x 5 mm MOSFET footprint3 mmslotjet7mm7 mm2.5-mm-tallfins3 mmfinned area Fin thickness, channel spacing 0.2 mm Finned area extended 1 mm beyond 5 x 5 mmperimeter of the MOSFET area Fins only modeled for the slot jet case. Future workwill model effect of fins on circular jet cases.Fins can be fabricated using a skiving process. Image fin dimensions:fin thickness 0.09 mm, channel width 0.18 mm, fin height 1 mmImage credit: Gilbert Moreno (NREL)NREL 16

Effect of Fins: Slot Jet20 Reduced thermal resistanceby 80% using finnedsurfacesThermal resistance, j-c [K/W]no fins– 50% lower thermalresistance (per device area)compare to the 2014 Accord151-mm-tall fins Finned surfaces increasepumping powerrequirements1050At 0.5 m/s, 24 devices candissipate 2,150 W of heat.Each device would dissipate 90 W at Tj 250 C.2.5-mm-tall finsspreader width (s) 10 mm, slot width (w) 1 mm0.00.20.40.60.81.0Jet velocity [m/s]NREL 17Initial Thermal DesignCFD temperature contours (sectional view)Initial resultsSlot jet: 2.5-mm-tall fins, w 1 mm, jet velocity 0.5 m/s Maximum Tj 234 C Each device dissipates 90 W 24 devices can dissipate 2,150 W Heat flux 358 W/cm210 mm10 x 10 mmü Flow rate requirements: 3.6 LPM(at this flow rate, the outlet fluidtemperature is predicted to be82.4 C)60 mmtop view40 mmü Volume: 0.06 liters (1/4 of thevolume available for the powermodule and cold plate)assume 25.4mm tallSpace for fluid manifold and caseside viewNREL 18

Future Work Evaluate effect of high fluid viscosity at lower temperatures onthe thermal performance Understand the dielectric properties of ATF to evaluate their useas a coolant Develop methods to cool the electrical connections usingdielectric fluid Design the entire cooling system and conduct an experimentalvalidation of the cooling conceptNREL 19NREL 20Conclusions Evaluating using dielectric fluids in a jet impingementconfiguration to cool the power electronics– Modeled circular and slot jets and the effect of addingmicrometer-sized fins– Ideal to use ATF as the dielectric fluids Developed a cooling concept that can meet thevolumetric thermal targets and thus enable achievingthe 100 kW/L power density target

AcknowledgmentsSusan Rogers, U.S. Department ofEnergyEDT Task LeaderSreekant [email protected]: (303)-275-4062For more information, contactGilbert [email protected]: (303)-275-4450Thank YouTeam MembersKevin Bennion (NREL)Emily Cousineau (NREL)Xuhui Feng (NREL)Bidzina Kekelia (NREL)Jeff Tomerlin (NREL)www.nrel.govNREL is a national laboratory of the U.S. Department of Energy, Office of Energy EfficiencyNRELa nationalEnergy,laboratoryof the byU.S.DepartmentEnergy, Officeof Energyand isRenewableoperatedtheAlliance forofSustainableEnergy,LLC. Efficiencyand Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiencyand Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Thermal Management and Packaging of High Temperature Automotive Power Electronics Gilbert Moreno 3D Power Electronics Integration and Manufacturing June 26, 2018 This presentation does not contain any proprietary, confidential, or otherwise restricted information. NREL | 2 Outline •Motivation and objectives •Describe the cooling systems currently used in automotive power electronics ...