The ability of silicon carbide (SiC) power devices to improve energy efficiency in electric vehicles (EVs) is starting to make headlines, and Denso’s portrayal of SiC technologies as a major building block in a decarbonized society is one such testimonial. Denso is projecting SiC power semiconductors as a key enabler in spreading the use of EVs, which is considered vital in reducing CO2 emissions.
The Japanese automotive supplier claims that its booster power module incorporating SiC semiconductors in EVs is 30% smaller in volume and generates 70% less power loss than a module based on conventional silicon power semiconductors. That, in turn, reduces the size of the booster power module and improves vehicle fuel efficiency.
Figure 1 Multiple SiC power semiconductors are built into booster power modules to output higher voltage than the input voltage. Source: Denso
Toyota has utilized these modules comprising SiC diodes and transistors in its new Mirai model, launched on 9 December 2020. In 2018, Denso supplied Toyota with SiC diodes that the carmaker used in its Sora fuel-cell buses.
SiC liaison with Toyota
Toyota’s SiC liaison with Denso goes back to the 1980s when the two companies joined hands to start basic research on this wide bandgap (WBG) semiconductor material. Fast forward to 2007, Toyota and Denso formally announced to jointly develop SiC semiconductors for practical use.
Then came the first breakthrough in 2014 when Toyota announced to use SiC power semiconductors in power control units (PCUs) in Prius, the gasoline-electric hybrid vehicle that the Japanese carmaker launched back in 1997. PCUs, which account for approximately 25% of the total electrical power loss, control motor drive power in hybrids and other vehicles with electric powertrains.
Figure 2 The PCU with silicon devices (left) is significantly larger than the PCU incorporating SiC devices (right). Source: Toyota
The SiC-based PCUs raised the energy efficiency of Prius by 10% as per the JC08 test cycle. Next year, Toyota announced to test these SiC-based PCUs in the Camry hybrid prototype and see how PCU’s internal voltage step-up converter and inverter improve voltage, current, and thermal management.
Denso has also adopted 150 mm SiC epi-wafers from Showa Denko K.K. (SDK) for its power control modules. The company is already using these modules in on-board battery chargers and quick charging stands for EVs.
SiC and Denso’s green ambitions
SiC semiconductors are becoming a pillar in Denso’s drive for green technologies. The Japanese supplier of automotive technologies and components calls this contribution to decarbonized society “REVOSIC” and plans to develop a range of technologies using SiC-based power modules. REVOSIC is a generic term that Denso uses for its SiC technology initiative to achieve high quality and low loss EV designs.
Compared to silicon power semiconductors, SiC’s advantages in supporting EV designs in high-temperature, high-frequency, and high-voltage environments are now widely recognized. Tomoo Morino at Denso’s Power Module Engineering Division acknowledges that SiC has a low resistance compared to silicon, so electric current can easily flow even at higher frequencies.
Figure 3 Low power in SiC devices when switching on and off enables more efficient current flow even at higher frequencies. Source: Denso
Not surprisingly, therefore, SiC MOSFETs are starting to replace the well-established silicon IGBTs in EV power modules after Tesla’s pioneering move to implement SiC components in traction inverters of Model 3 vehicles. While Tesla demonstrated the performance benefits of SiC components in traction inverters in 2018, Toyota and Denso had exhibited SiC’s value proposition in Prius PCUs back in 2014.
The chasm between the silicon and SiC worlds is narrowing, and it’s apparent from the traction SiC devices are getting in EV designs. At a time when CO2 emissions are a major driver for vehicle electrification, proponents like Denso, Tesla, and Toyota are a testament to its suitability in high-temperature, high-frequency, and high-voltage environments compared with conventional silicon.
Denso calling SiC semiconductors a major contributor to a low-carbon society is an important testimonial for this up-and-coming WBG technology. The Japanese automotive firm is aiming to achieve carbon neutrality in its manufacturing operations by 2035.
Majeed Ahmad, Editor-in-Chief of EDN and Planet Analog, has covered the electronics design industry for more than two decades.
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