Best of Both Worlds: FREEDM-Pair Switches for Power Devices

Wide bandgap semiconductors show tremendous potential as medium- and high-voltage power devices because of their capacity to work more efficiently and at higher temperatures.

Currently, though, their high cost impedes their widespread adoption over the prevailing workhorse and industry standard – insulated-gate bipolar transistors (IGBT) made from silicon – which generally work well but incur large energy losses when they are turned on and off.

Now, research from NC State University suggests that pairing these different switches inside power devices can improve performance while keeping costs relatively low.

Alex Huang, Progress Energy Distinguished Professor and founding director of the FREEDM Systems Center, and Xiaoqing Song, an electrical engineering graduate student, developed the so-called FREEDM-Pair, which combines the workmanlike advantages of the IGBT device with the high performance of silicon carbide wide bandgap devices.

The results show that the IGBT switch handles the high current flow, while the wide bandgap switch handles lower current and switching, maximizing the advantages of each switch.

Experimental results for a 6.5 kilovolt FREEDM-Pair showed a 70 percent switching loss reduction at a cost 50 percent higher than using an IGBT device by itself.

“We predict that the cost will continue to drop over time,” Song said.

Huang presented the research earlier this month at the 17th European Conference on Power Electronics and Applications in Geneva, Switzerland.