The 2024 World Silicon Carbide Conference was held in Wuhan with great success, and at the conference, many professionals in the silicon carbide industry also shared with us the current progress of the industry and the research progress of related industries.
Then this article will bring Mr. Xiao Kaixiang of Navitas Semiconductor to explain the high-voltage silicon carbide to create megawatt-level charging for electric long-distance trucks.
Mr. Xiao Kaixiang is the technical marketing manager of Navitas Semiconductor, a master's degree student in power electronics from Nanjing University of Aeronautics and Astronautics, and has been engaged in switching power supply design and power semiconductor industry for more than 10 years. He has worked in ZTE, Infineon and other companies.
The demand for electric trucks is increasing. According to data analysis, the market share of electric passenger cars in the United States is expected to more than double by 2030. However, the long-haul electric truck market is still in its infancy. Only 60,000 electric trucks were sold in 2022, accounting for 1% of the overall truck market. Although there are 110 models, the overall share is still small and still in the embryonic stage.
The United States and 26 other countries have signed a COP27 Memorandum of Understanding that by 2030, 30% of vehicles sold on the market must be electric or zero-emission vehicles. While zero-emission vehicles include a variety of energy types, they are subject to emission standards. By 2040, it will reach 100%.
The main problems for electric vehicles are charging anxiety and range anxiety. Solutions include NIO's battery swap solution and increasing the battery voltage from 400V to 800V or even higher. In terms of silicon carbide technology, the main focus is on fast charging, such as Huawei's Supercharger. These technologies are essential for the development of electric vehicles.
Nikola was an early pioneer of zero-emission electric trucks and fuel cell trucks in the United States, although its growth was not as expected. The company offers both electric and hydrogen-fueled trucks, both of which have distinct advantages in terms of power output and maximum power. However, charging time and battery life remain challenges.
The battery system of a hydrogen fuel cell vehicle undergoes a series of boosts and inverters to drive the electric drive system of the electric vehicle. The selection of silicon carbide devices requires high voltage requirements, especially in the field of electric trucks. The selection of silicon carbide devices is critical and should meet voltage and power requirements.
The future trend of electric trucks is to move towards higher power and higher voltage. At present, the battery system voltages commonly used in passenger cars are 400V and 800V. For electric trucks, without a cooling system, their power is not much different from that of a regular passenger car, and the battery voltage is 800V or 1200V. For a 1200V system, at least a 1700V SiC high-voltage device is required. With active cooling, a power level of 3.75 megawatts can be reached. As for why 800V is chosen instead of 1200V in some cases, it may be because in high-power switching circuits, it is necessary to choose a 1700V power device, otherwise the stress of the device may exceed the standard.
There are two main technical routes for silicon carbide devices: planar type and trench type. The planar type is simple to manufacture and low in cost, but the resistance per unit area is higher and the switching speed is slower. The trench type has better performance, but is complex to manufacture and has high temperature sensitivity. Trade-offs need to be made when selecting a device to meet the needs of electric vehicles.
Navitas' SiC MOSFET technology route is different from trench and planar gates, and is a new patented trench-assisted planar gate technology. This technique strikes a balance between planar and trench shapes, that is, some grooves are added to the planar device to adjust the internal resistance and the width of the conduction channel, thereby reducing the resistance and improving performance. Because it is a flat form, the manufacturing process is relatively simple, so the yield is higher, but at the same time, it can combine the advantages of the trench type. Most obviously, it has a lower temperature drift.
Navitas' silicon carbide products offer a voltage range of up to 6500V and are industrial and automotive qualified, and some are capable of high-power parallel testing. When used in parallel at high power, the Vth variation range is small, the device has better current sharing performance, and the long-term reliability is better. For example, for a 650V system, the endurance time is about 5.7 microseconds, while for a 1200V system, the endurance time can reach 3.5 microseconds.
In terms of battery systems, 400V battery systems are typically used, but for 650V, 750V and higher voltage systems, Navitas offers a broader product portfolio. Among them, 1200V and 1700V have the widest product range, covering a resistance range from 10mΩ to 295mΩ. These products are suitable for high-voltage battery systems, such as 800V or even 1200V systems, to meet the needs of electric vehicles.
In addition to the single tube, Navitas also offers other products such as bare dies for higher voltage applications. These products are already being used in the electric drive systems of some electric vehicles, such as some customers are using die with encapsulated modules.
Navitas' trench-assisted planar grid structure has excellent dynamic temperature characteristics. At high temperatures (175°C junction temperature), the temperature drift rate is low, which can be reduced by more than 18%, compared to other competitors. This means that Navitas products perform better in high-temperature environments, with less heat generation and lower temperatures.
As shown above, the test data shows that Navitas' SiC MOSFETs are 26°C lower and have more than 5W less losses than the competition under the same conditions. This means lower switching and conduction losses, higher efficiency and better reliability.
The use of Navitas' silicon carbide-based devices will help reduce carbon emissions by approximately 25 kilograms per device, bringing significant environmental benefits.
Finally, an emerging application area is electric flying cars. Although companies such as Xpeng have received a lot of attention, battery voltages in this area are generally high, such as 800V, 900V and 1000V. In these applications, the selected devices are typically rated at voltages of 1200V and 1700V. This emerging application area deserves attention.
Summary of the charging head network
Navitas' trench-assisted planar grid structure combines the advantages of planar and groove shapes, adding a number of grooves to a simple manufacturing process, adjusting the internal resistance and the width of the conduction channel to reduce resistance and improve performance. It exhibits a low temperature drift rate under high temperature conditions and maintains stable performance. In addition, it has been tested to show a 20 to 50 percent performance improvement over the competition in some cases, showing lower losses and better heat dissipation. This structure is not only simple and inexpensive to manufacture, but also improves the stability and efficiency of the device, which can bring more reliable performance to applications such as electric trucks.