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Silicon carbide device ‘will boost EV efficiencies by 10%’

22 May, 2014

Toyota and the automotive parts supplier Denso have developed a silicon carbide (SiC) power semiconductor for use in automotive power control units (PCUs) which, they say, will boost hybrid vehicle (HV) efficiencies by 10% and reduce PCU sizes by 80%, compared to systems based on silicon devices. Toyota plans to start test-driving vehicles fitted with the new PCUs within a year.

SiC power semiconductors have low power losses when switching, allowing efficient current flows, even at high frequencies. Their losses are about 10% those of silicon devices, and they can operate at frequencies ten times higher.

This allows the coil and capacitor, which account for around 40% of the size of a PCU, to be reduced in size.

PCUs play a vital role in hybrid EVs and other vehicles with electric powertrains. They supply electrical power from the battery to the motor to control vehicle speed, and also send energy recovered during braking to the battery for storage.

An existing silicon-based hybrid vehicle power control unit (left) compared to the expected size of a future PCU based on silicon carbide devices (right)

PCUs currently account for about 25% of the total electrical power losses in a hybrid vehicle, with an estimated 20% of this being associated with the power semiconductors. Therefore, improving power semiconductor efficiency is a key to improving fuel efficiency. Since it launched its Prius petrol-electric HV in 1997, Toyota has been working to develop power semiconductors and to improve HV fuel efficiency.

Toyota and Denso have been collaborating on SiC devices since the 1980s. Toyota has used their jointly developed SiC power semiconductors in PCUs for prototype HVs. Driving these on test courses has confirmed a fuel efficiency increase of at least 5%.

Toyota recently established a clean room facility dedicated to the development of SiC semiconductors. It sees high-efficiency power semiconductors as a key technology for improving fuel efficiency for HVs and other vehicles with electrified powertrains. It says it will continue to boost development activities aimed at early implementation of SiC power semiconductors.

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