Volvo Bus Corp. and Swiss technology group ABB are collaborating to develop and commercialize hybrid- and full-electric buses that employ “open standards-based” dc fast-charging systems. Buses will be charged quickly through an automatic roof-top connection system (ACS) at bus stops, or through cabled charging systems overnight.
The first joint project, for the Luxembourg public transport system, involves the implementation of automatic e-bus chargers and up to 12 Volvo plug-in hybrid-electric buses, which will be operated by Sales-Lentz and run on existing public bus lines as of 2015, the companies said in a July 21 announcement of the global partnership.
Volvo Bus plans to deliver the first six plug-in hybrids in 2015, and six more in 2016.
The Volvo plug-in hybrid bus, which will officially debut at the IAA exhibition in Hanover, Germany, in September, is equipped with a 150-kW (70-kW continuous) electric motor powered by a 600-V, 19-kW·h lithium-ion battery, as well as a 5.1-L Euro 6 diesel engine that produces 240 hp (179 kW) and 918 N·m (677 lb·ft).
“Volvo continues to develop the modular system with customized components for the purpose, such as the hybrid/diesel, electric motor, energy storage, and power converters,” a spokesperson said.
The bus can be driven about 7 km (4.3 mi) on electricity alone and is said to reduce energy consumption by 60% and CO2 emissions by 75% compared with a conventional diesel bus.
Volvo Bus expects to begin commercial manufacture of plug-in hybrid buses toward the end of 2015. It intends to supply the new range in bus sizes from 10.5 m (34.5 ft) and longer, according to the spokesperson.
The company’s first full-electric buses will be launched in June 2015 within the ElectriCity project in Gothenburg, Sweden. They promise an 80% reduction in energy consumption and 99% reduction in CO2 emissions.
The fast-charging solution with Volvo is different than the “flash charging” system ABB developed for electric buses operating as part of a TOSA pilot project in Geneva, Switzerland. (Read more on this development at http://articles.sae.org/12293/.)
“This new system uses the learnings from the TOSA Geneva system and also uses automatic charging with no overhead cables, but it is not flash charging,” Gert Miedema, Senior Director, Marketing for ABB Fast Charging Products, told Truck & Bus Engineering.
For the TOSA project, a 400-kW “energy boost” charges the onboard batteries in 15 s at intermediate bus stops; a charge is needed every 1 to 1.5 km (0.6 to 0.9 mi), or every two to three bus stops. At the end of the route, the TOSA bus is charged in 3 to 4 min at 200 kW, and at the depot, charging takes about 30 min at 50 kVA.
For the Volvo project, a charge is needed every 7 km for the hybrid bus and every 15 km (9.3 mi) for the electric bus, according to Miedema. The power requirements are lower: 150 kW for the hybrid and 300 kW for the electric bus. Charging times range from 2 to 6 min during the day, depending on the configuration of the Volvo bus and the time available at the end points.
“Overnight recharging of the Volvo bus (and balancing of batteries) is taking approximately 2 to 4 hours, again depending on the [bus] configuration,” he said. “At the depot, fast chargers will have lower power levels.”
So, which charging system is better for which use? “This is a question of the charging time constraints and topography/environment of the bus route,” Miedema explained. “If the operator aims to have a burst of no longer than a minute at all its bus stops, TOSA is more appropriate. This could be the case in transportation between terminals at airports but also in inner cities with a lot of traffic and short distances between bus stops.
“In contrast, it may be more economical to use the Volvo system for an operator, as you need [fewer] charging stations along the route; in many historical inner cities, it may not be viable to install many charging stations because of historical heritage reasons or other architectural constraints.”
The two systems can “co-exist” in the same city on the different routes, he added, depending on the needs of the bus service operator.
Standardization of automatic dc fast charging is a key part of the Volvo project. Specific areas to be explored include the communications protocol between the infrastructure charging solution and the e-bus; electrical interface; and specification of the ACS, which is located on the roof of the bus and automatically connects to the fast charger at select charging stops.
An electric-bus charging standard will be largely based on the recently adopted global dc fast-charging standards for passenger cars, according to ABB. Its off-board dc fast charger uses the CCS (EN61851-23) protocol.
“The standard protocol Volvo and ABB see as the best fit for e-bus charging is the Combined Charging Standard, or CCS, which is also supported by the SAE body,” Miedema said. “Other elements are the 4 pole pantograph and wireless communication standard. The standardization efforts for e-bus charging will take place via IEC (International Electrotechnical Commission) and UITP (International Association of Public Transport) and later other organizations like SAE might be involved.”