Electrical and Computer Engineering
"With existing technology, a variable speed drive for an AC electric vehicle could be built with off-the-shelf parts for about $10,000. We want to reduce this to $2,000."
"It's an excellent example of how industry and universities can work together..."
Right Photo: VPEC's new active load dynamometer with an electric vehicle drive train was built to test soft-switching configurations for a project to cut the cost of electric vehicles. The dynamometer was built by graduate student researchers Dimos Katsis (pictured), Scott Frame and Dong Ho Lee, with equipment and assistance from GE. As an undergraduate Katsis worked on the solar car and hybrid electric vehicle projects. "Working on those teams as an undergraduate gave me systems integration and teamwork experience," he said. "This has been very useful with my work at VPEC. When working on the system integration for this test bed, I understood some of the practical limitations and difficulties in electric vehicle drive trains."
Driving Down the Cost of Electric Vehicles
Electric vehicles should become less expensive as a result of Department power electronics research. The hybrid electric car shown at the right was designed and converted by Virginia Tech students in 1994/95 as part of a College of Engineering student project.
The two-year project's goal is to reduce the size and cost of electric vehicle drive trains. Along with the batteries, the drive trains are responsible for the high cost of electric vehicles. "With existing technology, a variable speed drive for an AC electric vehicle could be built with off-the-shelf parts for about $10,000," said Professor Fred Lee, VPEC director. "We want to reduce this cost to $2,000."
The team hopes to achieve the cost and size reduction by improving the inverter - the system that provides AC power from a DC source. The project involves four major groups aiming at developing several modular components. IXYS Corporation is developing new power semiconductors that integrate the required control circuits within the insulated gate bipolar transistor (IGBT) modules. Analog Devices, Inc., is developing a single-chip analog/digital induction motor controller, to replace an array of components required today. VPEC is developing the soft-switching technology and the inverter control algorithm; and General Electric's Electric Vehicle Motors and Controls Department, in Salem, Virginia, is serving as the prime contractor and inverter/system integrator.
"It's an excellent example of how industry and universities can work together," commented Jim Crowgey, manager of AC electric vehicle engineering at GE. "Each team member has an area of expertise, and the combined team is very effective at integrating this expertise to develop a next generation inverter."
"We are trying to build a low-cost inverter with technology that would be applicable to both on- and off-road vehicles," Crowgey said. The goal is to make the drive train commercially available for on-road vehicles in late 1997 or early 1998. GE is looking at near-term opportunities in electric buses, and forklifts. It is the lower horsepower off-road forklift version that is projected to be produced in quantity the soonest.
Although the project is specifically aimed at electric vehicle motors, the technology will be applicable to other variable-speed AC motors. This means that the eventual market impact of the technology being developed is tremendous, according to VPEC Director Fred Lee. "What we are developing could impact the entire electric drive industry. It reduces energy consumption and polluting emissions," he said.
"The entire industry is moving from DC to AC drives," said Dick Booth, GE senior design engineer. AC induction motors are more reliable, more rugged, and use less energy due to efficiency and lower weight. "There also are cost and top speed advantages in going to AC," he added.
AC motors are more reliable and efficient than DC motors, but much more difficult to drive at variable speeds. "Most drives today are constant speed, and consume 50 percent of electric energy worldwide," Lee said. "If these constant speed motors were to be replaced by variable speed drives, one third of the energy cost would be saved," he added. According to the Electric Power Research Institute (EPRI), that would lead to the elimination of 640 power generation plants - and a positive environmental impact.
"In this project and others, we are seeking a low-cost approach to variable speed drives," said Dusan Borojevic, a co-principal investigator on the project. VPEC is attacking the area from two angles; the development of a soft-switching technique to reduce EMI and power loss, and the development of a digital controller to improve performance and efficiency.
Reducing the switching loss yields a more efficient, more reliable system. The fundamental limitation is that the semiconductor device cannot handle the heat from the loss. By reducing the heat and stresses on the devices in the circuit, the overall size and cost of the components involved can be reduced. "For example, with a more reliable semi-conductor device, you can make an 80 KW inverter more reliable - not as subject to overheating," Lee explained. "Before, your only choice was to overdesign the inverter for, say 100 KW - and the larger engine costs more and has higher operating costs."
The work at VPEC is an extension of the center's expertise in developing novel soft-switching conversion technologies and high-power semiconductor devices. "This project is interesting because it involves low battery voltage of between 250 and 400 volts DC and a high motor current," said Scott Frame, a graduate student researcher on the project. "The other soft switching techniques that could be used in this application are more suited for high voltage applications of 500 to 800 volts DC," he added.
In order to test the system under development, VPEC researchers, with help and equipment from GE, built a full-power dynamometer with an electric vehicle drive train. Operating at 100KW was a new record for VPEC. Previously the largest power converter had been 20KW.
However, records do not last long in power electronics. VPEC is now developing a 200 KVA converter for an auxiliary power supply for Kohler, a major manufacturer of power systems for mobile homes, yachts and electric power generation for remote areas.