Charging technology for hybrid buses

Siemens is supplying the charging technology for hybrid buses used on a bus route in Stockholm. The buses, which are equipped with a combined electric-diesel drive system, were manufactured by Volvo Bus Cooperation, with which Siemens is cooperating on electric bus systems.

Each bus’s electric motor has a maximum output of 150 kilowatts (kW) and gets its energy from a lithium-ion battery on the vehicle roof. Quick-charging stations at the final stops recharge the batteries within six minutes. A fully loaded bus can travel up to seven kilometers solely on electricity. During a one year test phase in Gothenburg, the Volvo 7900 hybrid buses that were equipped with systems designed by Siemens and Volvo used approximately 80% less fuel than diesel buses. On average, the buses were able to cover 70% of the route solely on electricity – quietly and without producing any emissions. The new charging technology makes buses lighter.

Siemens offers the drive motors, the energy transducers, and the external charging stations for regular-service electric buses. The fully automatic fast-charging stations in Stockholm were supplied by Siemens, as were the rails for the electrical contact and the communications unit on the roof of each bus.

Fully charged in six minutes

The charging station consists of a grid connection with a power converter and a transformer as well as a charging tower with a contact arm. As soon as a bus arrives at a charging station, a wireless connection is established via WLAN so that the bus can be identified and the requirements of the battery management system queried. Sensors then check whether the bus is correctly positioned. As soon As soon as the bus driver pulls the hand brake, a pantograph descends from the charging arm to the roof of the bus, and recharges the battery within six minutes with an output of 300 kilowatts. The battery’s charge level is displayed to the bus driver, who can terminate the recharging process by simply releasing the hand brake. The charging process automatically ceases when the battery is fully charged.

The major advantage of the new technology is that almost all of the charging infrastructure is contained in the station. Each bus requires only a WLAN communication box and two parallel lightweight contact rails. This solution significantly reduces vehicle weight compared to pantograph-equipped buses. To make even more electricity available, charging stations can also be installed along bus routes.

Volvo and Siemens had previously supplied a hybrid bus system to Hamburg, where it went into operation in December 2014. Through their partnership, Volvo and Siemens intend to develop a charging infrastructure standard that would make it easier for cities to switch over to the use of electric buses.