Universities using converted electric Scion xB for V2G research

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Image: AC Propulsion eBox.JPG

After five years and 70,000 mi (113,000 km), the first eBox's range still exceeds 100 mi (161 km).

AC Propulsion's all-electric eBox adds to its ongoing vehicle-to-grid (V2G) investigative role at the University of Delaware (UD) with a complementary research assignment at Technical University of Denmark (DTU).

Built from a 2006 Scion xB that was stripped of its internal-combustion engine and related systems, the eBox uses a drive system consisting of an ac induction motor, inverter, bidirectional charger, and battery management system. Capable of 0-60 mph (97 km/h) in 7 s, the eBox has a top speed of 95 mph (153 km/h), energy consumption of 220 to 320 W·h/mi (354 to 515 W·h/km), and driving range of 100 to 145 mi (161 to 233 km).

With 5088 cylindrical cells, the eBox's lithium-ion battery pack has 32 usable kW·h at a nominal charge of 345 V. The eBox's drive system provides 120 kW of propulsion power and up to 18 kW of charging power.

In the summer of 2011, DTU researchers took delivery of an eBox to further their V2G research efforts.

According to Peter Bach Andersen, a Ph.D. student involved with V2G research at DTU's Centre For Electric Technology (CET), ongoing investigations at the center include grid impact studies to determine how the electrical power distribution system handles the power consumption needs of EVs, as well as smart charging scenarios in which the timing of an EV's recharging is based on energy costs, grid capacity, and other factors.

"While DTU has done some EV research before, it has never been with a V2G-capable EV. The eBox is one of the first EVs in Denmark to have this capability," Bach Andersen told AEI.

Denmark's offshore wind farms will factor into CET's V2G research tasks.

EV charging will be indirectly linked to wind production via the energy market. If a lot of wind energy is available during certain hours, the energy cost will be lower and the EV will choose to charge at those hours.

"Smart charging should, in general, support better utilization of wind energy," said Andersen. "And V2G can move this EV/wind synergy even further by delivering stored wind energy back to the grid at later times. Future power markets will most likely facilitate a tighter link between EVs and wind."

Willett Kempton, a professor in UD's Department of Electrical and Computer Engineering and UD's lead V2G researcher, told AEI that writing software code and designing hardware to control vehicle charging have been the primary UD goals during the past two years. The work is being done so that EVs "have the practical devices needed to be a resource for the electric power system, including ancillary services and buffering renewable energy," he said.

AC Propulsion President and CEO Tom Gage told AEI that UD's V2G research work has already netted a number of specific benefits: "The operation of eBox vehicles by UD over the past three years has shown that AC Propulsion's drive system and battery system are capable of mixed use—meaning transportation and grid support—which is what we expected."

UD's research findings prompted AC Propulsion engineers to refine and improve various onboard vehicle charger control systems—namely the user interface, the battery management system, and operational interlocks. The UD studies also have underscored a need for regulatory and institutional changes, so that V2G can work within the existing utility infrastructure as well as have compatibility with electrical codes, according to Gage.

Although low-volume eBox fleets are providing a framework for obtaining valuable information for V2G researchers, high-volume EV fleets will make V2G applications practical.

Said Kempton: "The commercialization of V2G requires enough vehicles to meet the minimum bid level for ancillary services markets, such as the ability to produce power when there is a failure of generation or transmission elsewhere on the grid. Across grid areas, the minimum bid level ranges from 300 kW to 1 MW. With the eBox, about 100 of those vehicles would be required for a reliable 1 MW ancillary service commitment—30 would be required for 300 kW. Vehicles with smaller power capability than the eBox would require proportionally more vehicles to make the minimum."

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