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High Temperature Air-Cooled Power Electronics Thermal Design Annual Progress Report Scot Waye

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High Temperature Air-Cooled Power Electronics Thermal Design Annual Progress Report Scot Waye High Temperature Air-Cooled Power Electronics Thermal Design Annual Progress Report Scot Waye NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy Operated by the Alliance for Sustainable Energy, LLC This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Management Report NREL/MP-5400-62784 August 2016 Contract No. DE-AC36-08GO28308 High Temperature Air-Cooled Power Electronics Thermal Design Annual Progress Report Scot Waye Prepared under Task No. VTP2.7000 NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy Operated by the Alliance for Sustainable Energy, LLC This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. National Renewable Energy Laboratory Management Report 15013 Denver West Parkway NREL/MP-5400-62784 Golden, CO 80401 August 2016 303-275-3000 • www.nrel.gov Contract No. DE-AC36-08GO28308 NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Cover Photos by Dennis Schroeder: (left to right) NREL 26173, NREL 18302, NREL 19758, NREL 29642, NREL 19795. NREL prints on paper that contains recycled content. High-Temperature Air-Cooled Power Electronics Thermal Design Susan Rogers (APEEM Technology Technical Barriers Development Manager) Subcontractor: National Renewable Energy Laboratory The use of air as a coolant has several benefits, (NREL) drawbacks, and challenges. Air is free, it does not need to be carried, it is benign (no safety or environmental concerns), and Sreekant Narumanchi (NREL Task Leader) it is a dielectric. As a heat transfer fluid, however, it has a Scot Waye (Principal Investigator) number of drawbacks. Air has a low specific heat, low density, National Renewable Energy Laboratory and low conductivity. These make it a poor heat transfer fluid 15013 Denver West Parkway and cause a number of design challenges. To reject the high power densities required by electric-drive power electronics Golden, CO 80401 using the heat transfer coefficients achievable with air, large Phone: (303) 275-4062 increases in wetted area are needed. When increasing the E-mail: [email protected] wetted area, spreading resistance, fin efficiency, weight, volume, and cost need to be considered. Due to the low Start Date: FY11 specific heat, larger mass flows of air are required to remove Projected End Date: FY14 the heat. This can lead to parasitic power issues, especially coupled to the pressure loss of extended surfaces. This requires careful consideration of the system coefficient of Objectives performance. Depending on the location of the inverter, The overall project objective is to develop and apply air- environmental loads and ducting to better air sources may cooling technology to improve power electronics thermal need to be considered. Location can also affect the need for management design and influence industry, enhancing system noise suppression for the prime mover (blower/fan). For performance to help meet the U.S. Department of Energy example, the Honda system incorporated a silencer [1] (DOE) Advanced Power Electronics and Electric Motors because the inverter was located in the passenger (APEEM) Program power electronics technical targets for compartment. To push heat transfer performance higher, weight, volume, cost, and reliability. This overall objective small-channel heat exchangers can be used, but filtering must includes the following: be addressed. If needed, filtering can add pressure drops and maintenance issues may need to be addressed. • Develop and demonstrate commercially viable, low-cost air-cooling solutions for a range of vehicle applications and assess their potential for reducing the cost and Technical Targets complexity of the power electronics cooling system The 2015 and 2020 DOE APEEM Program technical • Enable heat rejection directly to ambient air, simplifying targets for power electronics are applicable for a 30-kW the system by eliminating liquid coolant loops, thereby continuous and 55-kW peak power inverter. improving weight, volume, cost, and reliability • Collaborate with Oak Ridge National Laboratory (ORNL) Accomplishments to demonstrate the feasibility of using a high-temperature, air-cooled inverter to achieve DOE technical targets • Shifted modeling efforts that optimized heat exchanger • FY 14 objectives included: geometries to experimental efforts • − Prototype and test optimized heat exchanger. Improve Tested baseline and optimized sub-module heat models based on test results. Down select best exchangers for maximum junction temperatures of 150°C design for prototype module to 300°C • − Test baseline and optimized heat exchangers. Extrapolated results to inverter scale Extrapolate results to inverter level, including balance- • Target heat load of 2.7 kW was dissipated at various flow of-inverter components and balance-of-system rates for each of the configurations metrics • Combining optimized heat exchanger with other inverter − Within electrical topology constraints, test module- components (excluding housing), estimated power density level heat exchanger design for thermal performance. and specific power exceeded 2015 technical targets Results will feed into improved design and future high- • Module-level heat exchanger tested with one-side and temperature, air-cooled inverter demonstration with two-side heat generation, dissipating 150 kW to 450 kW of ORNL. heat with maximum junction temperatures of 150°C to 300°C. 1 Waye – National Renewable Energy Laboratory circulating liquid metal flow loops to enable forced-air cooling [11]. Introduction Approach All commercially available electric-drive vehicles, with the notable exception of the low-power Honda system, use liquid- Project cooled power electronics systems. All the heat from a vehicle, • Use a system-level approach that addresses the cooling however, must ultimately be rejected to the air. For liquid- technology, package mechanical design, balance-of- cooled systems, heat from the power electronics is transferred system, and vehicle application requirements to a water-ethylene glycol coolant via a heat exchanger and • Research each of these areas in depth and apply findings then pumped to a separate, remote liquid-to-air radiator where to develop effective system-level designs the heat is rejected to the air. Air cooling has the potential to • eliminate the intermediate liquid-cooling loop and transfer heat Develop experimental and analytical/numerical tools and directly to the air. processes that facilitate high-quality and rapid research results Eliminating the intermediate liquid-cooling loop using • Investigate the effect high-temperature power direct air cooling of the power converter can reduce system semiconductor devices have on air-cooled inverter design complexity and cost by removing or reducing the pump, coolant lines, remote heat exchanger, remote heat exchanger • Work closely with industry, university, and national fan, and coolant. To realize these gains, however, effective laboratory partners to ensure relevant and viable system-level design of the direct air-cooled system heat solutions. exchanger, fan, and ducting is needed. Decoupling the The objective of this project is to assess, develop, and inverter/converter from the liquid cooling system also has the apply air-cooling technology to improve power electronics potential to provide increased flexibility in location. Honda took thermal management design and influence industry’s advantage of this benefit by placing its 12.4-kW power products, thereby enhancing the ability to meet DOE technical electronics system behind the rear seat of the vehicle cabin targets for weight, volume, cost, and reliability. This research and integrating it closely with the battery thermal management effort seeks to develop the necessary heat transfer technology system [1]. and system-level understanding to eliminate the intermediate As power electronics semiconductor and electronic liquid-cooling loop and transfer heat directly to the air. The packaging technology advances, higher allowable junction relative merits of air-cooled, high-heat-flux automotive power temperatures will further expand the feasible designs and electronics thermal management systems and the influence of benefits of direct air-cooled power electronics. Currently, high-temperature, wide bandgap semiconductors on this silicon insulated gate bipolar transistors have a maximum design space will be quantified, evaluated, and demonstrated allowable junction temperature between 125°C and 150°C under steady-state and transient conditions.
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