China's Tesla Rival NIO Produces its First C-Sample Silicon Carbide Drive Unit for the Upcoming ET7 Sedan

author: FutureCar Staff    

The NIO ET7 will include a silicon carbide inverter in its electric drive unit for greater efficiency.

Electric vehicle startup NIO Inc., which is often referred to as the "Tesla of China", plans to use a new silicon carbide (SiC) electric drive system in its future EVs, beginning with the new ET7. NIO announced the first C-Sample of its new SiC powertrain rolled off the assembly line on June 22, Chinese news outlet Gasoo reported. 

In the automotive industry, a C-Sample refers to a fully functional sample product manufactured with series production tools in order to evaluate the unit and manufacturing process before production begins at scale.

The SiC drive unit will be first used in the upcoming ET7, NIO's first sedan and third model following the launch of the fully-electric NIO ES8 and ES6 SUVs in China.

Many EV manufacturers are working to introduce SiC technology in electric vehicle inverters, which is an important part of the system.

In an electric vehicle, the inverter works by converting direct current (DC) to alternating current (AC) and controls the flow of electricity from the battery or from the battery pack to the electric motor. More importantly, the inverter controls the rapid flow of power to the motor when the driver demands it, such as during hard acceleration. 

Silicon carbide inverters offer higher efficiency gains compared with conventional inverters using silicon semiconductors because they produce less heat and are less temperature-sensitive. SiC EV powertrains also have lower cooling demands and a smaller form factor, making them ideal for electric vehicles where size and weight are concerns.

For the Model 3, electric carmaker Tesla became the first company to add SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) to an inverter design the company sourced from STMicroelectronics. It reduces the overall weight of the inverter to 4.8kg, which is less than half the weight of the inverter in the 2019 Nissan Leaf, which weighs in at 11.1kg. 

By using a SiC inverter to control the current flow, more power is available at the wheels, so an EV's powertrain can be made smaller, lighter and operate more efficiently. This reduction in weight translates to a longer range, but also allows for smaller electric motors to be used without sacrificing power output. 

NIO's next-generation electric drive unit.

Silicon carbide also delivers higher thermal conductivity, which is important for high-revving, high-voltage electric motors to prevent overheating.

As automakers switch from 400-volt electrical systems to more powerful 800-volt systems, the role of the inverter is becoming more important as part of the overall system, as it can deliver higher current more efficiently. The Porsche Taycan electric sedan is an example that uses a 800-volt system.

South Korea automaker Hyundai was one of the first automakers to commercialize 800-volt systems with its new Electric-Global Modular Platform (E-GMP), which underpins the IONIQ 5 SUV. 

Hyundai says the crossover model can reach an 80% charge in 18 minutes on a fast charger. This is roughly a fifth of the time a conventional 400-volt car needs to reach the same charge. Using an SiC inverter means more of this power is made available to drive the vehicle.

The NIO ET7 will come with a 180 kW permanent magnet motor for the front wheels and a 300 kW induction motor in the rear. The maximum power is rated at 480kW. The EV can go from 0 to 60mph in 3.9 seconds. However, by using NIO's new second-generation high-efficiency powertrain with a SiC power module, the vehicle's energy efficiency can be further improved.

The first ET7 prototype rolled off the assembly line on May 13 at the JAC-NIO Advanced Manufacturing Center in Hefei. The first deliveries of the ET7 are expected to start in the first quarter of 2022.

FutureCar Staff