Toyota and Denso develop SiC power semiconductor for power control units; targeting 10% improvement in hybrid fuel efficiency
|Toyota intends to leverage the benefits of high frequency and high efficiency of SiC power semiconductors to enable PCU downsizing of 80%. Click to enlarge.|
Toyota Motor Corporation, in collaboration with Denso Corporation (Denso) and Toyota Central R&D Labs., Inc. (Toyota CRDL), has developed a silicon carbide (SiC) power semiconductor for use in automotive power control units (PCUs). Toyota will begin test driving vehicles fitted with the new PCUs on public roads in Japan within a year.
Compared to silicon, SiC power semiconductors lose 1/10 the power and drive frequency can be increased by a factor of ten. This enables the coil and capacitor, which account for approximately 40% of the size of the PCU, to be reduced in size. Through use of SiC power semiconductors, Toyota aims to improve hybrid vehicle (HV) fuel efficiency by 10% under the Japanese Ministry of Land, Infrastructure, Transport and Tourism’s (MLIT) JC08 test cycle and reduce PCU size by 80% compared to current PCUs with silicon-only power semiconductors.
|Left:PCU with silicon power semiconductors (Production model). Right:PCU with SiC power semiconductors (Future target). Click to enlarge.|
In hybrids and other vehicles with an electrified powertrain, PCUs supply electrical power from the battery to the motor to control vehicle speed, and also send electricity generated during deceleration to the battery for storage. PCUs contain multiple power semiconductors, which are usually made of silicon; these power semiconductors account for more than 25% of semiconductors used in hybrids, according to Toyota.
However, PCUs account for approximately 25% of the total electrical power loss in hybrid electric vehicles, with an estimated 20% of the total loss associated with the power semiconductors alone.
Therefore, a key way to improve fuel efficiency is to improve power semiconductor efficiency, specifically by reducing resistance experienced by the passing current. ￼Due to the importance of power semiconductors, Toyota has been developing them in-house since launching the first-generation Prius gasoline-electric hybrid in 1997, and has focused on increasing their efficiency.
As an example, the Si power semiconductors used in the current third-generation Prius has one-quarter the power loss of those in the first generation.
As SiC enables higher efficiency than silicon alone, Toyota CRDL and Denso began basic research in the 1980s, with Toyota participating from 2007 to jointly develop SiC semiconductors for practical use.
|Toyota and Denso achieved the high efficiency SiC transistors through adoption of a trench structure. Source: Toyota. Click to enlarge.|
Toyota has installed the jointly developed SiC power semiconductors in PCUs for prototype hybrids, and test driving on test courses has confirmed a fuel efficiency increase exceeding 5% under the JC08 test cycle.
In December last year, Toyota established a clean room for dedicated development of SiC semiconductors at its Hirose Plant, which is a facility for research, development and production of devices such as electronic controllers and semiconductors.
In addition to improved engine and aerodynamic performance, Toyota is positioning high efficiency power semiconductors as a key technology for improving fuel efficiency for hybrids and other vehicles with electrified powertrains. Going forward, Toyota will continue to boost development activities aimed at early implementation of SiC power semiconductors.
Toyota will exhibit the technology at the 2014 Automotive Engineering Exposition, to be held from 21-23 May at the Pacifico Yokohama convention center in Yokohama.