Induction Charging Comes to Public Transit
Say goodbye to catenary wires. Utah State University has unveiled an electric bus that charges through induction, topping off its batteries whenever it stops to pick up passengers.
Designed by USU’s Wireless Power Transfer team and the Utah Science Technology and Research initiative’s Advanced Transportation Institute, the prototype Aggie Bus is already on the road. It uses the same wireless charging principle as an electric toothbrush or a wireless smartphone charger, except optimized for a massive public-transit vehicle.
As in all modern inductive-charging setups, a transformer is “split” between the bus and a charge plate under the bus stop. When the bus drives over the charging plate, current flows with no physical contact required. Engineers at USU designed their system so that the Aggie Bus can be misaligned up to 6 inches from the charge plate and still get 25kW of power and 90 percent efficiency from the power grid to the battery.
Because of the fixed routes they run and frequent stops they make, induction charging is ideal for buses. Instead of charging up a massive battery overnight before a route, the Aggie Bus features a smaller battery setup that recharges every time the bus reaches a predetermined stop. The smaller batteries free up interior space, reduce downtime and lower battery costs — although induction plates must be added to bus stops.
Though the Aggie Bus is a working prototype, USU is working with Wireless Advanced Vehicle Electrification (WAVE) — a company spun-out from USU — in order to bring a commercialized bus to market. In mid-2013, WAVE and the Utah Transit Authority are planning to unveil a 40-foot induction-charged transit bus on the USU campus that’s capable of taking a 50kW charge. The project was funded by USU, who will purchase the bus, and a $2.7 million grant from the Federal Transit Administration.
Charging a bus through induction may be a new idea in the U.S., but bus routes with similar wireless charging systems have been in place in Torino, Italy, since 2003 and Utrecht, the Netherlands, since 2010. Ideally, induction charging would be used in city centers to replace noisy, smoky diesel buses. It would also work on already electrified routes, allowing cities to take down unsightly hanging catenary wires.