Cree, Inc. and Kansai Electric Power Company of Osaka, Japan, have successfully demonstrated a 110 kVA silicon carbide (SiC) three-phase inverter. This represents the highest power SiC inverter reported to date and represents nine times higher output power than the previous high of 12 kVA demonstrated by KEPCO and Cree in 2004. Cree fabricated the SiC power devices and Kansai Electric (KEPCO) constructed the SiC modules and inverter using these devices, as a part of the collaborative eight-year effort funded by KEPCO. These inverters could eventually reduce conversion losses by more than 50 percent compared to existing silicon (Si) inverters.
An inverter is used in a variety of applications to convert power from DC to AC or for changing the operating frequency in variable-speed motor drives. Applications include heat pumps, industrial motors, and electric vehicles. Inverters are also used to transfer power onto the grid from battery, wind and solar sources.
“In the future, a tremendous amount of energy savings could be realized in industry by switching from Si inverters to SiC inverters because the power loss of the inverters is estimated to be reduced by more than 50 percent,” comments Dr. Yoshitaka Sugawara, executive researcher and manager of the SiC program at KEPCO. “Kansai Electric plans on further increasing the power capability of these inverters in order to apply them to a variety of power systems.”
“We are advancing SiC power device technology through a variety of improvements ranging from lower defect density crystal growth to improved epitaxial processes, device design and processing,” states Dr. John Palmour, Cree’s executive vice president of advanced devices. “While more development is required, these improvements are moving the technology closer to the point where a significant reduction in the need for new power plants and reduction in greenhouse gas emissions are possible.”
The SiC switching device developed for this inverter is a 4.5 kV, 100 A design called the SiC Commutated Gate Turn-off Thyristor (SiCGT), jointly developed by Cree and KEPCO. The chip size is 8mm x 8mm, enabled by a significant reduction in crystalline defect densities. This switch, which can turn off or on in less than 2 microseconds, has a 10 times higher switching speed than that of an equivalently rated silicon Gate Turn-off Thyristor (GTO). This device does not require a snubber circuit, a commonly used protective circuit for GTOs, thus reducing the part count and heat dissipation.
A SiCGT module was then developed that utilizes one SiCGT and one 6mm x 6mm SiC PiN diode in a metal can package. The module can operate at higher temperatures (300°C) than conventional silicon modules (125°C), by utilizing a new high-temperature resin, “Nanotec-resin KA100,” for dielectric insulation. Using six of these modules, the three-phase Pulse Width Modulation (PWM) inverter demonstrated an output power of about 110 kVA. The PWM frequency was 2 kHz.