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SiC Contributes to Smaller, More Efficient Power Units in EV (Electric Vehicles)

SiC devices deliver high switching speeds that enable the use of smaller peripheral components such as inductors, and compatibility with higher temperatures allows designers to reduce the size of heat dissipation and cooling measures.

ROHM, a pioneer in SiC (Silicon Carbide) development, acquired German SiC single crystal wafer manufacturer SiCrystal in 2009, providing a significant advantage over the competition by achieving a completely in-house, integrated production, from manufacturing crystal ingots to complete SiC devices, including SiC Schottky barrier diodes, MOSFETs, and full SiC modules that integrate both components in a single package.

Until now, we have focused on supplying 2nd generation planar-type SiC MOSFETs for automotive use (Fig. 1, Left), but recently we were able to become the first supplier in the industry to mass-produce trench-type SiC MOSFETs (Fig. 1, Right). These 3rd generations SiC MOSFETs achieve lower ON-resistance and larger current handling capability in a smaller area.

SiC MOSFETs
 Figure 1. ROHM 2nd Generation (left) and 3rd Generation (right) MOSFETs

Advantages of SiC Devices

A major advantage of SiC devices is greater efficiency compared to their silicon counterparts. This translates to shorter charge times when used in onboard (car) chargers, for example. In addition, SiC devices deliver high switching speeds that enable the use of smaller peripheral components such as inductors, and compatibility with higher temperatures allows designers to reduce the size of heat dissipation and cooling measures. SiC devices also feature superior breakdown voltage that supports the higher voltages used in the latest automotive battery systems, further increasing efficiency.

SiC Device Applications

The most advanced use of SiC devices is in onboard chargers, followed by DC-DC converters where higher voltages and efficiency can be achieved with SiC. The onboard charger functions as an AC-DC converter for converting AC voltage (100V to 240V) into a DC voltage to charge the high voltage battery. To ensure universal compatibility, the input allowable voltage of existing onboard chargers ranges from 85V to 265V, but market demands for shorter charge times call for the input allowable voltage to accommodate higher battery voltages, increasing the need for SiC.

DC-DC buck converters perform the function of switching power devices from high battery output to lower DC voltages using a transformer. SiC makes it possible to achieve high-performance DC-DC converters by minimizing switching loss along with the size of peripheral components.

Primary applications for SiC devices include inverters and electric compressors. Next, we will introduce a real-world example that shows the effects of adopting SiC devices in the main inverter of an electric vehicle.

Pioneering Technologies Through Formula E

ROHM which became the official technology partner of Venturi Formula E Team that competes in FIA’s Formula E Championships (the premier racing class for electric vehicles launched in 2014), supplies SiC power devices for the main inverter that comprises the core of the drive system.

ROHM has participated in Formula E since the fall of 2016 (see Photo 1 below). Adopting SiC in the main inverter makes it possible to reduce both the size and weight by improving efficiency and eliminating the need for heat sinks and other components. Season 3, which began in 2016, utilized a combination of silicon IGBTs (Integrated Gate Bipolar Transistors) and SiC Schottky barrier diodes that decrease inverter weight from 15kg to 13kg vs conventional silicon-based solutions. And in December 2017, for Season 4, ROHM replaced the silicon IGBTs with SiC MOSFETs, reducing weight even more, by 60% over Season 1, to only 9kg. As you can see, SiC delivers dramatically improved performance in a smaller form factor.

SiCrystal
Formula E Motorcar of ROHM Partner Venturi

Formula E races are held in the heart of urban areas to promote the advantages of electric cars. The extremely low noise threshold along with zero emissions allow races to take place in metropolitan areas such as Monaco, Paris, and New York. And recently, there were reports of organizers visiting Tokyo for the future season. We look forward to this ongoing development and hope that we will be able to see a race in Japan for the first time in the near future.

Further information at http://micro.rohm.com/en/formulae/

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