A semiconductor power switch developed by ECE power electronics researchers has been named one of the top 100 inventions of the year by R&D Magazine. The 41-year-old R&D 100 awards program honors the most technologically significant products, materials, or processes developed by the international community.
|Alex Huang (left) and Bin Zhang (right) with a set of ETO Thyristors developed for high-speed power switching.
High Frequency, High Power Breakthrough
The Virginia Tech Emitter Turn-Off Thyristor (ETO) was developed by Professor Alex Huang's team at the Center for Power Electronics Systems (CPES). It represents a breakthrough that will enable high-frequency and high-power systems, such as large motors and electric utility systems to use power electronics technology to improve equipment reliability and efficiency at a low cost.
The Drive for Faster Switches
Switches are used in almost every power conditioning application, either stepping up the voltage or current, or converting from ac/dc or dc/ac. Energy loss occurs as the switches change state, driving the search for faster switches to cut switching loss.
High frequency power electronic switches have been used for years in lower power equipment to condition power for optimal performance, but their use in high-power systems has been limited by cost and performance. With such devices applied to higher-power systems, the energy cost savings could reach tens of billions of dollars each year.
The Virginia Tech ETO can turn off 4000 A in less than 5 microseconds while blocking up to 4500V. Its high frequency switching capability of 1 kHz or higher can handle a peak current of 10,000 A and continuous current of 1,500 A. During the transition, it handles both high current and high voltage simultaneously.
"The ETO can withstand 16 MW of instantaneous power," Huang said. "It's like turning on 100 stoves instantly through a unit about the size of a graham cracker. And you can stop them all at once, too," he explained.
"This switch allows us to advance very high power converters from a line speed of 60 Hz to 1 to 3 KHz switching at the same power level. This speed allows us to chop the voltage into whatever shape is needed," he said.
Helping Replace Navy Steam Catapults
The technology is expected to be a boon to military power needs. For example, the ETO has been designed for inclusion in the power conditioning system for the U.S. Navy's new Electromagnetic Aircraft Launch System, which will replace current steam catapults aboard aircraft carriers. Other potential applications include electric propulsion for an all-electric military tank, submarine and destroyer propulsion drive systems, warship power generation and distribution systems, and ground-based laser systems.
Boosting Electrical Transmission
It is in the electric utility industry that ETO may save the U.S. economy the most, by improving quality and capacity of the transmission grid by 25 to 60 percent, according to Huang. "The increasing frequency of electricity outages are due primarily to lack of quick voltage support, leading to voltage collapse in many regions of the country and poor quality of power," he explained. He cited the low investment in electrical transmission infrastructure, and the need to increase the flow of power on existing lines. "This will increase the levels of fault currents and short circuit currents beyond the levels that can be safely handled by existing mechanical circuit breakers, driving the need for power electronic circuit breakers and fault current limiters using ETO technology," he said.
Additional potential ETO systems include industrial motor drives, and locomotive drives.
Although the ETO has the highest power handling capabilities of all solid-state switches, its greatest benefits could be its low cost and reliability. Other competing power switching technologies for high-power Gate Turn-Off Thyristor (GTO) and Integrated Gate Commutated Thyristor (IGCT) are complex and bulky with either less than half the switching speed (GTO), or costly (IGCT). The commercialized ETO switch is projected to cost less than $1000, compared with $1900 for a typical high frequency IGCT switch.
The ETO was developed as part of the CPES program to reduce the cost of power electronics technology by using integrated power electronic modules (IPEMs) composed of standardized components instead of custom designed and manufactured systems. ETO technology integrates commercial, low-cost GTO devices with low voltage power Metal-Oxide Semiconductor Field Effect Transistors (MOSFET) in a low inductance housing arrangement.
The ETO was developed with funding from the Department of Energy's Energy Storage Program managed by Sandia National Laboratories. The Tennessee Valley Authority also provided significant funding for the development. The American Competitiveness Institute worked with Virginia Tech in developing the manufacturing process.
In addition to Huang, Virginia Tech team members include graduate students Zhang, Aaron Xu, Tiger Zhou, Yunfeng Liu, Siriroj Sirisukprasert and Josh Hawley.
The technology has been licensed to Solitronics Inc., of Blacksburg, Virginia.