Next Generation New Energy Motor Controller Development - SiC Inverter
In the electric vehicle drive controller, the inverter is a key component for energy AC/DC conversion, and is used for energy recovery during driving or braking of the motor. The market is increasingly demanding for controllers in terms of energy transfer efficiency, power density, and price. The power module is the key component of the inverter to achieve high transmission efficiency and high power density. At present, most of the electric vehicle drive inverters are based on the traditional Si (silicon) device IGBT (insulated gate bipolar transistor) power module. The design has the disadvantages of low switching frequency and large loss, which limits the improvement of the power density of the electric vehicle driver.
SiC (silicon carbide) has three advantages over Si devices: higher breakdown voltage strength; lower loss; higher thermal conductivity. These characteristics mean that SiC devices can be used in high voltage, high switching frequency, high power density applications. With the improvement of SiC module power manufacturing level, SiC will be a more suitable semiconductor device for electric vehicle drivers. The use of SiC devices is an effective means to achieve high power density of electric vehicle drivers. At present, more and more researches have been applied to the application of SiC power modules to motor-driven inverters. Toyota Motor Corporation has applied SiC power modules to hybrid vehicles.
Compared with Si devices, the use of SiC devices has great advantages.
High efficiency and improved vehicle mileage
Since the turn-on voltage drop of the SiIGBT exhibits diode characteristics: even if the on-current is small, the IGBT has a large initial turn-on voltage drop. The turn-on voltage drop of the SiC MOSFET exhibits a resistive characteristic: its turn-on voltage drop is proportional to the turn-on current. The two different on-voltage characteristics of SiIGBT and SiCMOSFET determine that the conduction loss of SiCMOSFET is higher than that of SiIGBT only when the current is very large, and the conduction loss of SiCMOSFET is better than that of SiIGBT in most current intervals. In the whole vehicle working condition, most of them are small current working conditions, and the large torque working condition accounts for a small proportion in the whole road spectrum. With the development of SiC chip technology, the on-resistance of SiCMOSFET will be better than SiIGBT in the future.
Therefore, after using the SiC device, the conversion efficiency of the inverter can be significantly improved, so that for the same battery pack, the use of the SiC device can effectively improve the mileage of the entire vehicle.
Small size and high power density
Due to the low loss of SiC devices, SiC devices can achieve the same output power with a smaller chip area than Si devices. At the same time, SiC devices can operate at high frequencies, helping to reduce the size of passive components around the power device. The SiC inverter developed by United Electronics is more than half the volume of the approved Si inverter at the same power level.
High switching frequency to optimize system noise
At present, the common switching frequency of Si inverter is 5-10 kHz, and the system will generate 5-20 kHz switching noise, which is easy to cause discomfort in the frequency range that can be heard by the human ear. With the SiC device, by increasing the switching frequency to 40 kHz, the switching noise frequency generated by the system can exceed the frequency range that can be heard by the human ear. At the same time, the switching frequency is increased to help reduce the current control harmonics, thereby reducing electromagnetic noise and improving the driving experience of the vehicle.
But the current use of SiC devices also presents great challenges.
SiC devices are more expensive
Since the current SiC chip process is not as mature as Si, mainly for 4-inch wafers, the material utilization rate is not high, and the Si chip wafer has been developed to 8 inches or even 12 inches. On the other hand, the demand for SiC chips on the market has not yet increased, and on the other hand, the cost of SiC chips is relatively high.
SiC device packaging technology development lags behind
At present, many mainstream power device suppliers in the world have researched and developed SiC chips, but in contrast, the development of packaging technology for SiC devices lags behind. Compared with Si chip, SiC chip has higher temperature resistance and its operating temperature can exceed 200 degrees. However, the sealing technology used in SiC module is still designed with Si module, and its reliability and life cannot meet 200 degrees. Job requirements. The application conditions of the SiC chip are limited.
Drive protection technology
Compared with the Si chip, the short-circuit withstand capability of the SiC chip is greatly reduced. Therefore, in order to prevent short-circuit failure of the SiC device during operation, the drive circuit needs to have a lower response time, which is proposed for the protection technology of the SiC device drive circuit. A big challenge.
Thermal design
Since the area of a single SiC chip is small, in order to achieve high power output, it is necessary to use more chips in parallel. How to make reasonable layout design of the chip inside the module to ensure the thermal balance between the chips and monitor the hot spot temperature of the chip is a big challenge.
EMI and insulation problems caused by high switching speed
Compared with Si devices, the switching speed of SiC devices can be significantly improved, and the di/dt and dv/dt in the switching process are improved, although this helps to reduce the switching loss of the device, but on the other hand it will produce Serious EMI problems, how to properly design the control circuit and filter circuit to suppress EMI is also an important issue. At the same time, high dv/dt adversely affects the insulation of the motor windings, which may accelerate the aging of the insulating parts such as the enameled wire and the insulating ring, thus bringing new challenges to the insulation design of the motor.
to sum up
Although the current SiC device process is not as mature as Si, the development of SiC package is relatively lagging, and the price of the device is several times higher than that of Si. However, with the maturity of device technology and the increasing demand for SiC devices in the market, these disadvantages will be gradually smoothed out, and SiC devices are inherently high withstand voltage, high switching frequency, low loss and so on. The advantages also determine that it can be used more and more widely as a very competitive material in the future.
