POWEREFFICIENCY
Figure 6: The results from the electro- thermal simulations by engineers at Fairchild reveal the superiority of SiC BJTs in the boost stage. Losses are plotted versus the output current for the 8 kW boost converter in figure 4. It can be seen that the gain in efficiency using SiC compared to silicon is gets larger and larger as the load current is decreased (part load)
50
IGBT, but also 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, 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
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)
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.
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.
Figure 1 I-V-forward characteristics of the SiC BJT compared to the silicon IGBT. The BJT’s collector current, IC, is plotted as a function of the collector-emitter voltage at a range of base currents, IB, ranging from 250 mA to 1 A. The dotted red line represents the same parameters for the IGBT
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.
www.solar-pv-management.com Issue VII 2011
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56