Toyota hopes to increase fuel economy by 10 per cent with its next generation of hybrid power units.
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The company, in conjunction with supplier Denso, is currently developing a new power control unit that replaces silicon semiconductors with silicon carbide (SiC) versions.

According to Toyota, current power control units are responsible for up to 25 per cent of the electrical power loss in today’s hybrid cars, with the silicon semiconductors accounting for 80 per cent of that wastage.

Within Toyota’s Hybrid Synergy Drive system, the power control unit (PCU) is responsible for channelling power to the electric motor to regulate road speed or petrol motor assistance, as well as funnelling energy recovered from regenerative braking from the electric motor to the battery pack. The semiconductors within the PCU do the grunt work, switching power flow on and off.

When a silicon semiconductor is switched off, a tail current continues to flow for a short period of time afterwards. SiC versions don’t suffer the same problem, which allows them to work at higher frequencies. In addition they suffer less power loss than their silicon-only counterparts. Combined these efficiencies allow for the PCU size to be reduced by 80 per cent.

Silicon and silicon carbide semiconductor

The overarching aim of the project is to improve efficiency for electrified cars by 10 per cent under Japan’s JC08 fuel economy testing cycle. This regime is known to produce numbers that are more generous than those used by the US, the EU and Australia. For instance, the current Prius is rated at 3.1L/100km under JC08, 3.9L/100km in Australia and 4.7L/100km in the USA.

Toyota says that it plans to begin testing the new power control unit on public roads in Japan during 2015. It’s unknown at this stage whether Toyota and Denso’s new SiC power control unit will be available in time for the next-generation Prius or the company’s hydrogen fuel cell vehicle that’s due next year.