We are in the middle of the biggest change in the automotive industry’s history: shifting from well-established diesel and petrol engines to an all-electric future.
Inverters in automotive is a key example of a SiC technology use caseMillions of electric vehicles (EVs) are already being sold every year, but their technology is still developing rapidly — it’s clear that EV technology can still be improved, resulting in increased performance, reliability, and range, which will serve to attract even more customers.
Achieving these technology goals relies, in large part, on the power electronics within our EVs. Incumbent silicon-based devices have done a solid job, but now silicon carbide (SiC) promises substantial improvements for the automotive industry.
The advantages of SiC semiconductors in automotive applications
Silicon carbide is a wide bandgap (WBG) semiconductor, and this larger bandgap gives it some major advantages over silicon in power circuitry. Perhaps the most important is improved efficiency – and SiC can also operate at higher temperatures and voltages than silicon, and enable greater power density.
For EV applications, the efficiency of SiC is critical, as well as its ability to perform well at high temperatures and high voltages. The fundamental principles apply across the different types of hybrid vehicle (mild, conventional and plug-in) as well as full-electric battery EVs, although battery size and range will vary substantially, and there are additional complications in integrating with the conventional internal combustion engine (ICE) in a hybrid.
The higher power density achievable with SiC enables more compact designs for the EV’s traction inverter, which handles the conversion of DC power (supplied by the car’s battery) into the typically three-phase AC power that the electric motor needs, as well as the vehicle’s onboard charger (OBC), which converts AC power from the grid into DC, and its fast charging system for use with rapid, high-voltage DC chargers.
Rather than using a unidirectional OBC, adopting a bidirectional OBC enables power to flow in both directions, so it can be fed back to the grid from the car when desired – this is called vehicle to grid (V2G). By adopting a bidirectional design, it’s also possible to achieve higher efficiency compared to a unidirectional OBC, as diodes are replaced by SiC MOSFETs, thus eliminating losses from the diodes’ forward voltage drop.1
There is a shift in the EV industry underway from existing 400 V designs towards an 800 V bus architecture. To make this possible, the high voltage capabilities of SiC mean it is the key enabling technology.
A higher voltage means that current can be lower while still delivering the same power. Alternatively, batteries can be recharged faster by delivering more power without the need for advanced cooling. With the low current approach, charging cables could be thinner, reducing cost as well as saving weight and space.
As well as the vehicles themselves, the electrification of our cars depends on a reliable, effective network of chargers – ranging from plug-in chargers for home use, all the way to DC fast charging systems that can deliver a substantial charge in just a few minutes. Unsurprisingly, the high efficiency of SiC-based components makes them attractive in these applications.
SiC semiconductors in traction inverter design
Let’s take a more detailed look at one example application: the traction inverter in an EV. This is the most important component in an EV’s power train and converts the DC current from the battery into AC to drive the car’s traction motors.
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With the ongoing shift to renewable energy and the electrification of transport and industry, the demand for higher power and greater energy efficiency in electronics is increasing. Wide bandgap technologies including SiC and GaN bring many advantages.
WBG OVERVIEWWhile silicon has been used previously, the higher efficiency of SiC inverters makes them attractive. They can be smaller and lighter, while being superior to silicon at dissipating heat mitigates the need for cooling. In EVs, there is a direct relationship between weight and range — shedding weight results directly in greater range.
SiC’s ability to operate at higher temperatures and better thermal conductivity could enable more compact traction inverters with higher power density, saving valuable space and weight.
Switching to SiC can consequently increase range without requiring a larger, more costly battery. This efficiency is achieved with faster switching and lower on-resistance (RDS(ON)), which reduces conduction losses.
The traction inverter also needs to be robust, particularly as it is switching high power currents, with the likelihood of high dv/dt transients.
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Design considerations
Designing with SiC devices for automotive applications creates some new challenges, requiring careful consideration – SiC is not just a plug-in replacement for existing silicon-based components. For example, gate drivers for SiC devices are different from the equivalents used with silicon components.
The high power density of SiC-based systems creates new thermal challenges that must be considered, particularly because thermal stress is a significant factor impacting reliability. The high switching frequencies also mean that noise and EMI will be an issue, and suitable filtering is needed.
Automotive applications also require robust components that can handle high temperatures and harsh electrical environments. Devices must be qualified to automotive quality standards, such as AEC-Q100.
The future for SiC semiconductors in automotive applications
As previously mentioned, the automotive industry is moving from 400 V to 800 V bus voltages, primarily to enable faster charging even at higher battery capacity. This trend will likely mean increased interest in SiC MOSFETs rated up to 1200 V. There will also be more applications for V2G and bi-directional charging, which will create further use cases for SiC devices.
More generally, to enable carmakers to hit the sales targets for EVs that have been set by governments, they will need to deliver reliable, comfortable vehicles that have sufficient range, but are still affordable.
SiC semiconductors will play a vital role in making this possible, as well as improving the charging infrastructure needed by EVs. According to McKinsey, over 50% of battery electric vehicles could rely on SiC powertrains by 2027, compared with about 30% today.2
Making the right choice
While there are design challenges to consider, the benefits of moving to SiC can be substantial across a broad range of automotive applications.
Talk to Avnet Silica’s FAEs and power engineers today for expert information and guidance on the automotive sector, empowering you to make the right choices for your next power system design.
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