Toyota beginning on-road testing of new SiC power semiconductor technology; hybrid Camry and fuel cell bus
|SiC PCU under the hood of the Camry hybrid test vehicle. Click to enlarge.|
Toyota will begin the on-road testing of silicon carbide (SiC) power semiconductors in Japan this year, using a Camry hybrid prototype and a fuel cell bus. The tests will evaluate the performance of the SiC technology, which could lead to significant efficiency improvements in hybrids and other electric-drive vehicles. (Earlier post.)
Power semiconductors are found in power control units (PCUs), which are used to control motor drive power in hybrids and other vehicles with electric powertrains. PCUs play a crucial role in the use of electricity, supplying battery power to the motors during operation and recharging the battery using energy recovered during deceleration. At present, power semiconductors account for approximately 20% of a vehicle’s total electrical losses; raising the efficiency of the power semiconductors is a promising way to increase powertrain efficiency.
|SiC PCU. Click to enlarge.|
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.
The technologies behind these SiC power semiconductors were developed jointly by Toyota, Denso Corporation, and Toyota Central R&D Labs., Inc. as part of the results of a broader R&D project in Japan (the R&D Partnership for Future Power Electronics Technology under consignment from the New Energy and Industrial Technology Development Organization). The three had announced their joint development efforts in May 2014.
In the Camry hybrid prototype, Toyota is installing SiC power semiconductors (transistors and diodes) in the PCU’s internal voltage step-up converter and the inverter that controls the motor. Data gathered will include PCU voltage and current as well as driving speeds, driving patterns, and conditions such as outside temperature.
By comparing this information with data from silicon semiconductors currently in use, Toyota will assess the improvement to efficiency achieved by the new SiC power semiconductors. Road testing of the Camry prototype will begin (primarily in Toyota City) in early February 2015, and will continue for about one year.
|Brief presentation on Toyota’s newly developed silicon carbide (SiC) power semiconductor for use in automotive power control units from the May 2014 announcement. Click to enlarge.|
Similarly, on 9 January, Toyota began collecting operating data from a fuel cell bus currently in regular commercial operation in Toyota City. The bus features SiC diodes in the fuel cell voltage step-up converter, which is used to control the voltage of electricity from the fuel cell stack.
Data from testing will be reflected in development, with the goal of putting the new SiC power semiconductors into practical use as soon as possible.
|Camry SiC-equipped test vehicle. Click to enlarge.|