industry SiC transistors
Figure 7
Fairchild’s SiC BJTs can reduce the losses in the inverter stage if they are used to replace silicon IGBTs, according to calculations by the company. The losses are plotted versus output current amplitude, in the 8kW inverter circuit in figure 5. It can be seen that the gain in efficiency using SiC compared to silicon is relatively
getting larger and larger as the load current is decreased (part load)
and losses in the inverter stage by 65 percent. However, if cost, size and weight are considered as important factors – cost and weight are normally viewed in this manner – then the system designer should increase switching frequency. This reduces both the size of the choke in the boost stage and the inductances in the output filters. Even at four times the original switching frequency, 64 kHz, the losses associated with the SiC BJT are lower than those for the IGBT running at only 16 kHz. That four-fold frequency increase can nearly halve the cost, size and weight of the switch inductances, while producing less loss in the semiconductors.
show that the low switching losses in this wide bandgap device are greatly enhancing the system efficiency. If extremely low losses are the primary goal for the system designer, then the SiC BJT should be used at the same low switching frequency as the IGBTs, in this case 16 kHz.
Take that route, and according to our simulations, losses in the boost stage can be cut by 52 percent,
These simulations illustrate how SiC bipolar transistors can play a pivotal role in driving down the cost and size of power conversion systems in a wide range of applications, starting with the those containing switch inductances such as DC-to-DC converters and inverters with output filters. That, in combination with requirements on high efficiency, makes SiC BJTs an ideal choice in PV inverters and mobile equipment such as automotive DC-to-DC converters and traction drives.
Electrification within the automotive industry is proceeding at a rapid pace, and when this sector taps into the great set of attributes of the SiC BJT it will spur the development of smaller, easier to cool electrical systems.
© 2011 Angel Business Communications. Permission required.
24
www.compoundsemiconductor.net June 2011
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