Page 26 - EE Times Europe September 2021

26 EE|Times EUROPE

SPECIAL REPORT: EVs
SiC Cost Outweighed by Performance Gains

in EV Applications

By Maurizio Di Paolo Emilio

ower electronics solutions continue to be largely based on ence and a practice that can slow the pace of SiC adoption.
standard silicon devices. While three-level and other silicon Indeed, Mitsubishi engineers noted that customers remain in wait-
circuit topologies are emerging to improve efficiency, new sili- and-see mode. “If early adopters are successful with this technology,
Pcon carbide designs are emerging to meet growing high-power delivering the desired benefits, there’s going to be significantly more
requirements for electric vehicles. adoption, and I think we’re gradually working our way through that
In interviews, power devices managers at Mitsubishi Electric US phase,” said Mike Rogers, a power devices application engineer at
highlighted the promise of SiC when compared with standard silicon Mitsubishi Electric.
implementations. Design changes are required to make the best use of SiC, resulting
They said efficiency improvements can be achieved with hybrid in substantial reworking of PCBs. The resulting designs must be
technologies that combine silicon with SiC. For example, Si-based capable of handling much higher operating frequencies, the Mitsubishi
insulated-gate bipolar transistors (IGBTs) with SiC Schottky- engineers added.
barrier diodes achieve efficiency improvements with relatively minor
cost increases. For many applications, this represents a compromise EV, STORAGE APPS
between cost and performance. Automotive applications stand to benefit significantly from SiC tech-
Without changing topologies, SiC is one of very few ways to increase nology, especially for EV drivetrains along with battery recharging,
efficiency significantly, the Mitsubishi engineers asserted. either on-board or at charging stations.
“There is a strong desire to reduce the size and weight of electronics”
PRICEY SiC for EVs, said Tony Sibik, Mitsubishi power devices manager. “Silicon
SiC remains considerably more expensive than silicon. Hence, it’s carbide helps in that effort both by shrinking inverter size [and] by
important to identify applications in which the economics keep pace increasing efficiency, thus
with energy savings or some other technical advantage to justify the SiC remains more reducing the size of battery
cost. Mitsubishi Electric has focused on SiC for high-power devices needed for a given range,”
primarily because they are vertical components that operate at higher expensive than silicon, he added.
voltages. “Gallium nitride is a material that we have some experience Energy-storage applica-
with within our RF group,” said Adam Falcsik, product manager for so it’s important to tions on the scale of electrical
power devices at Mitsubishi Electric. “And we think it certainly has very identify applications in utilities are another potential
useful applications in lower-power applications. driver of SiC adoption. The
“So far, our power device development has focused on silicon which the energy savings sector is benefiting from the
carbide, primarily because it’s better-suited for higher-power applica- or a technical advantage shift to renewable sources
tions,” he added. “And so we have device modules [in production] rated such as solar and wind to
up to 1,200 A, and we have voltage ratings up to 3.3 kV.” can justify the cost. provide power when the sun
SiC technology is viewed as unproven and therefore risky by power doesn’t shine and the wind
engineers, who tend to be conservative. Many would prefer to wait for doesn’t blow.
evidence of reliable performance before taking the plunge — a prefer- Providing power during periods of peak demand requires sufficient
capacity to store energy and, therefore, more converters and inverters.
SiC is a promising candidate for those power-conversion steps.
As more alternative energy sources come online, power flow requires
special attention, including active filtering and harmonic correction.
All require power semiconductors. Meanwhile, wide-bandgap SiC tech-
nology promises to boost renewable energy storage.
One reason is that SiC delivers dielectric strength 10× that of Si,
thereby offering a framework for building devices operating at higher
voltages while meeting field requirements for remote charging infra-
structure and smart-grid applications. Moreover, higher switching
frequency allows designers to reduce the physical size of magnets,
inductors, and other filter components, including transformers.
Mitsubishi Electric engineers note that Si IGBTs, in general, have
relatively slow switching, which slows further as the blocking voltage
increases. IGBTs in the high-voltage range, such as 3.3 kV, are quite
slow and exhibit high switching losses, limiting them to low switching
frequencies.
“Silicon carbide offers its advantage for 3.3-kV and, shortly, 6.5-kV
devices,” said Eric Motto, Mitsubishi’s chief engineer for power devices.
“More importantly, they can switch at considerably higher frequencies
Mitsubishi Electric’s 3.3-kV SiC dual module is rated between than a silicon device ever could.”
325 A and 750 A. (Source: Mitsubishi Electric) Said Falcsik: “We’re seeing this today in … subway applications;

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