New Capabilities Quickly Predict Temperatures for Power Electronic Inverters

October 2007

Power electronics systems are key elements of hybrid electric, plug-in hybrid, and fuel cell vehicles. And the inverter, which conditions electrical power flowing between the battery pack to the electric motor, is the primary component of the power electronics system. Keeping the inverter cool is essential to its effectiveness and lifetime, so matching an appropriate cooling system to the inverter is a critical element in good vehicle system design.

NREL Power Electronics researchers are having success developing capabilities to quickly predict an inverter's dynamic heat generation and device temperature profile. This research will greatly improve our understanding of cooling requirements, and therefore facilitate cost-effective system design.

Graphic showing how heat dissipates (in blue) from the inverter in a pyramidal manner through metal plates and heat sink material on which the electronic components are mounted.

Graphic 1: The blue color shows the angle of heat dissipation as it travels through an inverter's layers.

Working with students from the Illinois Institute of Technology (IIT) and researchers at the Oak Ridge National Laboratory (Oak Ridge), NREL researchers applied finite element analysis to accurately predict electronic package thermal profiles and correlate an empirical equation to describe heat dissipation from an inverter (in particular the extent to which the heat dissipates at various angles as it travels through the device's various layers - see graphic 1). That three-dimensional "spreading angle" was then used to enhance a model developed at Oak Ridge, which predicts dynamic temperature fluctuations for the electronic components over time from the amount of heat generation. Transient thermal analysis over an extended vehicle drive cycle might take more than a day with finite element analysis but now can be done in less than five minutes. Data collected from an NREL hybrid-electric vehicle fit the model prediction very well.

This is a vital step in selecting appropriate cooling systems for particular inverters. NREL researchers will continue to work with IIT and Oak Ridge to make the modeling more accurate and robust and to integrate the modeling process into future power electronics research and development. See graphic 2 for a schematic of the analysis process. For more information contact NREL engineer Michael O'Keefe.

A schematic shows that vehicle test data goes through simulation models such as PSAT Prius Model, MG2 Shaft Torque and Speed, and ORNL Inverter Loss Map, to then derive temperature and heat generation.

Graphic 2: Vehicle test data is collect and analyzed through various simulation models to determine temperatures and heat generation.

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