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The future of SiC IGBT-PET?

SiC SBD and MOS are currently the most common SiC-based devices, and SiC MOS is competing for share with IGBTs in some areas. We all know that IGBT combines the advantages of MOS and BJT, and the third-generation wide-bandgap semiconductor SiC material has better characteristics than traditional Si. So why is SiC MOS the most common one. Where is the SiC IGBT?

We all know that Si-based IGBTs are still in the dominant position, and with the development of the third-generation wide-bandgap semiconductor material SiC, SiC-related devices have appeared one after another, and are trying to replace IGBTs in related industries. For example, new energy vehicles, SiC power devices are fully entering the field, such as Tesla’s SiC MOS parallel solution, and various semiconductor manufacturers are fully deploying automotive-grade SiC MOS modules. According to the characteristics of the SiC materials we mentioned earlier, more High-power, high-frequency, and high-power density Electronic controls are slowly emerging. Since the advantages of SiC in materials and IGBTs in devices are so obvious, why is there no SiC IGBT?

First of all, cost is a key factor considered for the survival of each company. As far as SiC power devices are concerned, there is not much price advantage. It is conceivable that the price of SiC IGBTs is very high in most applications.” Uncompetitive”. Some industries are no longer technology-oriented, but cost as the main factor, and SiC IGBTs are not used. Even the “not bad money” new energy automobile industry currently only covets SiC MOS. Therefore, cost is currently the most critical factor for the “survival” of SiC IGBTs!

So where is the SiC IGBT most likely to appear first in the future? The answer is what we are going to talk about today-power electronic transformer PET, also known as solid-state transformer SST or smart transformer ST. Generally refers to the realization of new power electronic equipment with traditional power frequency AC transformer functions but not limited to it through the combination of power electronic technology and high-frequency transformer.

PET is generally used in medium and high voltage applications, on-board converters for electric locomotive traction; smart grid/energy Internet, and distributed renewable energy power generation and grid integration. Advantages: good compatibility, high controllability and good power quality. The following figure is a structural diagram of a low-voltage distribution network based on traditional power frequency AC transformers and power electronic transformers. You can understand what PET is:

Image source network, intrusion

At present, PET still has the following problems or bottlenecks: low power conversion efficiency, low power density, high cost and poor reliability. The main factor causing the bottleneck is the limited withstand voltage level of the power semiconductor devices used therein, which leads to the need to adopt a multi-cell cascading topology for 10kV voltage, resulting in a considerable number of power devices, energy storage capacitors, and inductors.

It can be seen that in order to make a breakthrough, a power semiconductor device with higher withstand voltage and lower loss is born-SiC IGBT!

Due to the voltage capacity, upper frequency limit, and allowable operating temperature of Si-based IGBTs, there are no more breakthroughs in the application of PET. And the advantages of the third-generation wide-bandgap semiconductor SiC we mentioned earlier are that the breakdown electric field is particularly strong, the forbidden band width is large, the electron saturation drift speed is fast, and the thermal conductivity is high, so that it can meet higher frequency and higher resistance. High voltage, higher power and other occasions, can make the current PET of power electronic transformers break through the bottleneck and take it to the next level~

Some people will ask, why not SiC MOS? As we mentioned at the beginning, in addition to material advantages, there are also device advantages! As the blocking voltage increases and the operating junction temperature increases, the most intuitive thing is that the on-state resistance of SiC MOS will also increase significantly, resulting in large losses, making it unsuitable for devices with voltages above 10kV . The SiC IGBT will have superior on-state characteristics, as well as switching speed and a good safe working area, which will “show its skills” in the 10kV~25kV occasions.

Therefore, it is not impossible, but existence is reasonable! Today’s content I hope everyone will like it~

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