The power supply of EVs is shifted to silicon carbide.
Among the electronic components of EVs, the main inverter has the greatest power and the greatest potential for improving efficiency, which is responsible for converting DC from the battery to AC at the input of the electric motor.
When it comes to electric vehicles (EVs), efficiency is paramount. There are many opportunities to improve performance, especially in the driveline, and one key area is power electronics. Among the elements based on electronics, the main inverter has the greatest power and the greatest potential for improving efficiency, which is responsible for converting direct current at the output of the battery into alternating current at the input of the electric motor. In the last few years, there has been a significant increase in the use of silicon carbide (SiC) semiconductors in EV inverters, replacing the typical insulated silicon gate bipolar transistors (Si IGBTs). The use of SiC enables the design of higher density power modules that can operate at higher temperatures, leading to new requirements for heat management and the use of new materials for EV power electronics.
Switch to SiC
Despite the higher price of SiC-based MOSFETs, their use in electric vehicle applications is already significant. According to IDTechEx research, in 2020 SiC MOSFET inverters accounted for nearly 30% of the global EV market. Tesla started this trend in 2018, and others, as exemplified by BYD, are just developing their vehicles in this technology. EV giants such as Stellantis and Hyundai are increasingly using SiC electronics in their emerging models as part of the introduction of high-voltage platforms (800 V). New IDTechEx report entitled 'Power Electronics for Electric Vehicles 2022-2032' illustrates the transition to SiC, presenting an in-depth analysis of power electronics for the EV market with examples of EV models, supply chain, packaging materials and innovation.
Temperature management challenges
Power electronics in electric vehicles pose significant challenges in terms of temperature management, and the use of SiC changes several aspects of module and housing design and influences the choice of materials. In a traditional power electronics package, there are several potential points of failure during thermal cycling. As the packet heats up and cools down, differences in thermal expansion between materials degrade various connections, including wire connections, attaching semiconductor structures, and attaching the substrate. In SiC packages, the power density and operating temperature can be significantly increased, which means that some traditional options are not suitable.
Figure 1: Traditional power electronics package with potential thermal failure points (marked in red). Source: © IDTechEx 'Electric vehicle heat management 2021-2031'.
Currently, aluminum wire is the dominant connection technology, but such connection is also a frequent cause of failure. This led to greater use of joining wires from aluminum alloys, copper and even lead. Semiconductor fastening materials are also essential: this is usually done with traditional solder, but at higher operating temperatures (especially with SiC), the standard SAC (tin-silver-copper) alloy can be unreliable leading to alternatives emerging. such as silver sintering, providing much better thermal cycle performance. The Tesla package from STMicroelectronics uses a combination of copper band bonds and silver sintering aluminum wire ties to fix the die. IdTechEx forecasts further dissemination of these options in inverter designs, which is to ensure higher reliability and reliability in smaller housings.
Very often, the EV power electronics are liquid-cooled, where the coolant flows through the heat sink fins under the module. While this method of managing the temperature of the power electronics may not be as innovative as the new materials used in the battery pack itself, it still offers interesting possibilities for integration throughout the vehicle. Many vehicles use the same coolant path through the power electronics and electric motor. For example, on some models, waste heat can be extracted from the drivetrain to heat the cab, helping to reduce losses and improve the overall range of the vehicle, especially in cold weather.