Author: Ali Husain, senior marketing and strategy manager of semiconductor industry and cloud power
The International Energy Agency (IEA) estimates that motor power consumption accounts for more than 45% of the world’s total electricity. Therefore, it is very important to find a way to maximize its operating energy efficiency. More energy efficient drives can be smaller and closer to the motor, reducing the challenge of long cables. From the perspective of overall cost and continuous reliability, this will have practical significance. Wide band gap (WBG) semiconductor technology is expected to play an important role in the realization of new motor energy efficiency and dimensional reference.
WBG materials such as silicon carbide (SIC) can be used to produce similar products with better performance than silicon (SI). Although there are important opportunities to use this technology, industrial motor drives are gaining the most interest and attention.
The high electron mobility of SiC enables it to support faster switching speed. These faster switching speeds mean that the corresponding switching losses will also be reduced. Its dielectric breakdown field strength is almost an order of magnitude higher than that of silicon. This results in a thinner drift layer, which translates into a lower on resistance value. In addition, since the thermal conductivity of SiC is three times that of Si, it is much more efficient in heat dissipation. Therefore, it is easier to reduce the thermal stress.
Traditional high voltage motor driver will use three-phase inverter, in which Si IGBT integrated anti parallel diode. Three half bridge phases drive the corresponding phase coils of the inverter to provide a sinusoidal current waveform, which then makes the motor run. The energy wasted in the inverter will come from two main sources conduction loss and switching loss. Using SiC based switch instead of Si based switch can reduce these two losses.
SiC Schottky barrier diodes can be integrated into the system without anti parallel silicon diodes. Silicon based diodes have reverse recovery current, which will cause switching loss (as well as electromagnetic interference, or EMI), while SiC diodes have negligible reverse recovery current. This reduces the switching loss by up to 30%. Since the EMI generated by these diodes is much lower, the need for filtering is not so great (resulting in a smaller bill of materials). It should also be noted that the reverse recovery current will increase the collector current when conducting. Since the reverse recovery current of SiC diode is much lower, the peak current through IGBT will be smaller during this period, so as to improve the reliability level of operation and prolong the service life of the system.
Therefore, if we want to improve the driving efficiency and extend the working life of the system, it is obviously advantageous to move to SiC Schottky. So how can we go further? If SiC MOSFET is used to replace IGBT which is responsible for the actual switching function, the improvement of energy efficiency will be more significant. Under the same operating conditions, the switching loss of SiC MOSFET is five times lower than that of silicon-based IGBT, while the conduction loss can be reduced by half.
Other related benefits of WBG include significant space savings. The excellent thermal conductivity provided by SiC means that the required radiator size will be greatly reduced. With smaller motor drivers, engineers can mount them directly on the motor housing. This will reduce the number of cables required.
Anson semiconductor now provides engineers with IGBT packaged with SiC diodes. In addition, we have 650 V, 900 V and 1200 V rated SiC MOSFETs. With such products, it is possible to change the motor drive, improve the energy efficiency parameters and simplify the implementation.