The role of silicon carbide in next-generation industrial motor drives

The International Energy Agency (IEA) estimates that motor power consumption accounts for more than 45% of the world’s total electricity. Therefore, it is crucial to find ways to maximize the energy efficiency of its operation. More energy-efficient drives can be smaller and closer to the motor, reducing the challenges of long cables. This will make sense from an overall cost and ongoing reliability standpoint. The advent of wide bandgap (WBG) semiconductor technology is expected to play a major role in enabling new benchmarks in motor efficiency and form factor.

By: Ali Husain, Senior Manager, Marketing & Strategy, ON Semiconductor Industrial & 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 crucial to find ways to maximize the energy efficiency of its operation. More energy-efficient drives can be smaller and closer to the motor, reducing the challenges of long cables. This will make sense from an overall cost and ongoing reliability standpoint. The advent of wide bandgap (WBG) semiconductor technology is expected to play a major role in enabling new benchmarks in motor efficiency and form factor.

The use of WBG materials such as silicon carbide (SiC) enables the manufacture of similar products that outperform silicon (Si). While there are various significant 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 speeds. 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 enables thinner drift layers, which translates into lower on-resistance values. Furthermore, since SiC has three times the thermal conductivity of Si, it is much more efficient at dissipating heat. Therefore, it is easier to reduce thermal stress.

The role of silicon carbide in next-generation industrial motor drives

Traditional high-voltage motor drives use three-phase inverters with Si IGBTs integrated with anti-parallel diodes. The three half-bridge phases drive the corresponding phase coils of the inverter to provide sinusoidal current waveforms, which in turn make the motor run. The energy wasted in the inverter will come from two main sources – conduction losses and switching losses. Replacing Si-based switches with SiC-based switches reduces both of these losses.

SiC Schottky barrier diodes do not use anti-parallel silicon diodes and can be integrated into systems. Silicon-based diodes have reverse recovery currents that cause switching losses (and generate electromagnetic interference, or EMI), while SiC diodes have negligible reverse recovery currents. This enables switching losses to be reduced by up to 30%. Since these diodes produce much lower EMI, the need for filtering is not as great (resulting in a smaller bill of materials). It should also be noted that reverse recovery current increases the collector current at turn-on. Since the reverse recovery current of SiC diodes is much lower, the peak current through the IGBT will be smaller during this period, increasing the reliability level of operation and extending the life of the system.

The role of silicon carbide in next-generation industrial motor drives

Therefore, migration to SiC Schottky is clearly advantageous if the drive efficiency is to be improved and the operating life of the system to be extended. So how can we take a further approach? If the IGBTs responsible for the actual switching function are replaced by SiC MOSFETs, the energy efficiency gains will be even more pronounced. Under the same operating conditions, the switching losses of SiC MOSFETs are as much as five times lower than those of silicon-based IGBTs, while conduction losses can be reduced by as much as half.

Other related benefits of the WBG scheme include substantial space savings. The excellent thermal conductivity provided by SiC means that the size of the heat sink required will be greatly reduced. Using a smaller motor driver, engineers can mount it directly on the motor housing. This will reduce the number of cables required.

ON Semiconductor now offers engineers IGBTs co-packaged with SiC diodes. Additionally, we have SiC MOSFETs with 650 V, 900 V and 1200 V ratings. With such a product, it will be possible to revolutionize motor drives, improve energy efficiency parameters, and make implementation more streamlined.

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Author: Yoyokuo