There are many electronic power devices made of silicon carbide, and the most popular one is the inverter for electric vehicles. What is an inverter? The inverter is an device, which changes the direct current into the alternating current.
1. An Indispensable Inverter for Electric Vehicles
Electric cars are powered by batteries. The current, which is generated by the battery directly connected to the resistor, is direct current. Then, it comes to electronic power devices.
The power electronic device includes converters, electronic switches, and electronic AC power controllers.
- In some occasions, it is necessary to change the AC power supply into a DC power supply, which is the rectifier circuit;
- If it needsto change the DC power supply into an AC power supply, this reverse process corresponding to rectification is defined as an inverter circuit;
- Aconverter can be used as both a rectifier circuit and an inverter circuit. The converter includes rectifier (AC to DC<AC/DC>), inverter (DC to AC<DC/AC>), AC converter (AC inverter<AC/AC>), DC converter ( DC Chopper <DC Chopper>).
Electric vehicles need to convert direct current into alternating current, so inverters are needed. The role of silicon carbide is to act as an inverter for electric vehicles. The Tesla Model 3 inverter includes silicon carbide devices (24 silicon carbide MOSFETs).
Actually, there are many applications of silicon carbide in electric vehicles, like an inverter:
Power converter: The use of silicon carbide can improve the high temperature performance of the power converter to above 300°C, thus reducing the volume of the heat dissipation system. However, the traditional Si-based converter has a large loss. The engine part needs a cooling system to keep its temperature at 105°C, while the power converter part requires a cooling system to keep its temperature at about 70°C. Therefore, two sets of cooling systems must be used to meet different requirements. This greatly increases the volume of the cooling system of electric vehicles.
Battery charger: Silicon carbide or gallium nitride can increase the working frequency of the converter and increase the power density. The PFC converter, AC/DC converter and DC/DC converter together form the battery charger. Nowadays, the market of on-board chargers for electric vehicles has gradually adopted silicon carbide SBD. The products are concentrated in 1200V/10A and 1200V/20A. Each on-board charger requires 4-8 silicon carbide SBDs.
The third one is the inverter. The usage of SiC devices can significantly reduce losses, like SiC BJT and SiC MOSFET. The loss of the inverter composed of SiC BJT is reduced by 53%; when the frequency increases, the loss will be further reduced. When the switching frequency is 15kHz, the loss of the SiC BJT inverter is reduced by 67%.
In fact, the commercialization of silicon carbide devices is not long ago. In 2001, SiC SBD was commercialized, and in 2010, SiC MOSFET was commercialized.
2. Reasons for Applications of Silicon Carbide in Electronic Power Devices
Why choose silicon carbide to apply in electronic power devices? Reasons are as below:
The speed of electric vehicles is changed by the frequency and amplitude of the alternating current. Under the condition of voltage 600-800V, the switching frequency is 4-10kHz, the basic AC frequency of up to 1kHz can be generated, and the total power level range can reach 50-250kW. Of course, silicon carbide materials with high-frequency, high-power and excellent performance is chosen.