Cool Running Autos: HEVs and EVs

On December 22, 2010, in HEV, TMS, by juliann

This is an excerpt from an article that ran in Power Systems Design in August 2010. This article was authored by Thomas Sleasman and Birol Sonuparlak from Thermal Management Solutions, Rogers Corporation, Chandler, Arizona, U.S.

Cooling of IGBT based power modules for Hybrid Electric and Electric Vehicles

It has been forecast that by 2020 there will be upwards of 10 million passenger and light truck vehicles sold annually that are powered entirely or in part by electric motors. Starting with the leadership of Toyota’s first Hybrid car launched in 1997, significant progress in various power train electrification designs have been made by every major OEM, especially during the last five years.

Today’s Hybrid Electric Vehicle Power Module Market

Hybrid drive systems use a combination of an internal combustion engine (ICE) and one or more electrical motors (EM). Variations in hybrid drive systems depend on how the EM and ICE of a power train connect, and also when and at which power level each propulsion system contributes to powering the vehicle.

There are two types of HEV drive systems, series or parallel. The parallel system is currently used by almost all the major OEMs. Parallel hybrid systems can be further categorized as assist, mild and full hybrid. The Toyota Prius and the Ford Escape are examples of full hybrids, as they can run on just the ICE, the EM or a combination of both. Mild hybrids on the other hand do not run on EM only. The EM provides additional power as required while the ICE still provides the primary power for the power train. Honda’s Integrated Motor Assist (IMA) is such a mild hybrid. A third hybrid drive system is the plug-in hybrid (PHEV). These should be increasingly popular in the future. PHEV allows the driver to choose the mode of operation. The driver can choose the EM mode of operation for short distance commuting or the independent ICE mode of operation for long distance driving. The PHEV’s larger battery can be charged using standard voltages from a typical power grid system.

HEV/EV Power Module Solutions – Cooling, Heat Dissipation

The efficient dissipation of heat generated by Insulated Gate Bipolar Transistor (IGBT) based power modules used to control these electric drive designs is critical to system quality and reliability. Design concepts such as integrating inverter, DC-DC converter and electronic control unit, along with reducing the number of IGBT power chips, are helping design engineers to lower the size and weight of the power train and significantly reduce the power train cost. Reducing the size and populating more components in a confined space increases the challenges of thermal management. Well engineered thermal management is required to cool electronics and maintain electrical performance within a given envelope of HEV/EV operation, and efficient thermal management provides long term reliability by minimizing thermally induced stresses.

Today, most HEV/EV inverter systems use liquid cooled IGBT power modules for thermal management. Although there are still power module designs utilizing air cooled power modules in design and production, we believe that future IGBT power modules for HEV/EV applications will continue to use more direct liquid cooled IGBT modules and move heat away from these modules more efficiently. A schematic representation of IGBT power module with pin fin heat sink is illustrated in Figure 1.

Integrated Pin Fin, direct liquid cooling base plates eliminate thermal grease interfaces between the IGBT module and the heat sink. This is a performance advantage that is realized in HEV/EV IGBT power modules beyond the standard base plate technology currently used in power modules for Rail/Traction power IGBT modules. Today, 70 to 80% of standard power modules for HEV/EV use base plates. There are also power modules on the market that do not use base plate solutions. These solutions also eliminate the solder joint between the DBC and base plate, and are present in such products as the SKAI IGBT System and Danfoss Shower Power® cooler system.

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