This is a power control unit (PCU) for a hybrid vehicle. Because the silicon-based semiconductors aren’t particularly energy efficient, Toyota is testing silicon-carbide semiconductors for the application, as it has less electrical resistance.
Power semiconductors are used in the power control units (PCUs) for hybrids and electric vehicles. Â Generally, these semiconductors are based on silicon.
The PCUs do such things as supplying battery power to the motors and recharging the battery during deceleration.
When it comes to electric powertrains, energy efficiency in all aspects is essential.  And it turns out that the typical power semiconductors account of some 20% of a vehicle’s electrical losses.
So Toyota—which is somewhat synonymous with hybrid technology, as it offers 12 models (Toyota and Lexus brands) in the U.S., which accounted for 62% of all hybrid sales in 2014, and as it has sold 2.4-million hybrids in the U.S. during the past 15 years—is testing a new semiconductor material for PCUs. The material is silicon carbide (SiC). SiC has less electrical resistance than straight silicon, so it is anticipated that using SiC semiconductors in PCUs can reduce the losses in the system.
They’re running two tests on the SiC power semiconductors in Japan.  The semiconductors were developed by Toyota and Denso Corp.
In one test, there are SiC-based transistors and diodes in the PCU internal voltage step-up converter and inverter that control the motor of a Camry hybrid prototype.
In another test, there is a fuel cell bus running in Toyota City that has SiC diodes in the fuel cell voltage step-up converter (it controls the voltage of the electricity from the fuel cell stack). Both tests will run for about a year, and the results will drive the development of SiC-based semiconductors.Â
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