TOSA (trolleybus optimisation système alimentation or optimized charging system for trolleybus) is a flash-charging connection technology developed by ABB that can automatically charge an electric bus in 15–20s, without affecting passenger capacity or journey times.
The bus connects to an overhead high-power charging contact when it pulls into a stop and charges the batteries during the time passengers are embarking and disembarking
TOSA keeps a battery bus on the road without resorting to either large, heavy and space-consuming energy storage or frequently having to take the bus out of service for a deep and full recharge. A fundamental difference between buses and automobiles is that buses follow fixed routes. The question of ‘range of operation’ which is of significance to electric cars is reduced to the more manageable ‘distance to next recharging opportunity’ for a bus. With buses predictably stopping at regular intervals, charging points can be located at the stops. With the bus being able to top up its charge at these points, the need for large and heavy batteries is avoided and the vehicle becomes lighter, more agile, more energy efficient as well as providing more space for passengers inside. Furthermore, if charging time can be limited to the time that the bus needs to stop anyway, negative effects on the schedule can be avoided.
At selected passenger stops, the TOSA system connects the bus to the charging infrastructure, and in 15–20 seconds, the batteries are charged with a 600-kilowatt power boost. The high-power charging of the high-power density batteries on the bus can result in load peaks affecting the local grid. The flash charger station, however, flattens out the demand by charging batteries located on the wayside over a period of a few minutes while drawing a lower current from the grid. As this current is up to 10 times less than would be the case without storage, the connection can be made with a cheaper and more readily available low-power supply. The system is inherently safe because the overhead connectors are only energized when they are engaged, and the electromagnetic fields associated with inductive charging concepts are avoided.
With limited time being available at stops (passengers typically embark and disembark in 15 to 25 s), as little time as possible should be lost in establishing the electrical connection – the Energy Transfer System does this in under a second. As the bus approaches a stop it is the driver’s responsibility to oversee the safety of the passengers and pedestrians and keep an eye on surrounding traffic. To avoid placing additional demands on the driver, the connection system is automatic. A laser aligns the moving equipment on the bus roof with the static overhead receptacle, and the connection is made as soon as the brakes are applied.
An additional few minutes charge at the final terminal enables a full recharge without interrupting the bus schedule. As operating costs for a bus service are highly dependent on driver wages, schedule frequency and fleet size, the change from diesel to electric supply should not reduce the commercial average speed nor require an increase of the fleet size to provide the same service. It was this requirement that led to the creation of two types of feeding stations along the route: the flash station and the terminal station. The flash stations provide a short high power boost of energy. However, drawing 600 kW for 15 to 20 s is not sufficient to fully recharge the batteries. More prolonged charges of four to five minutes at 400 kW are thus delivered at the terminus where buses are scheduled to stop for longer periods (in order permit the driver to take a break and to provide some recovery buffer in case the bus is running late). The time required for recharging at the terminus should thus not risk causing the bus to fall -behind its schedule or to be unable to catch up when it running late.
According to ABB, the TOSA fast-charging can save as much as 1,000 tons of carbon dioxide on a line covering 600,000 km per year. It also offers operating cost savings of 30% compared to an equivalent diesel-transit system.
The TOSA project was initiated by ABB in partnership with Swiss companies TPG, OPI and SIG. A TOSA demonstrator has been running in Geneva, Switzerland since 2013, and has operated for more than 500,000 km and saved more than 1,000 tons of carbon dioxide emissions. Since 2019, the system has been used on 20 e-buses in Nantes, France.
In China, King Long Motor Group, one of largest bus and coach manufacturers, and ABB have signed an agreement to jointly develop an e-bus with the TOSA flash-charging system. King Long will design and assemble the e-bus, while ABB will provide the TOSA flash-charging solution consisting of a wayside feeding station, an energy transfer system and an on-board battery charger. China is the world’s biggest market for e-buses, enabled by a government policy that prioritises the electrification of the public transportation system to reduce urban pollution and its dependence on oil imports.
In India, the government is promoting the use of electric vehicles, in some cases planning on mandating it, to reach 30% market penetration by 2030. Ashok Leyland, India’s largest bus manufacturer, and the fourth largest manufacturer of buses in the world and ABB Power Products and Systems India Limited, the standalone legal entity of ABB’s Power Grids business in India, have signed a memorandum of understanding (MoU) to expand the eco-system for efficient and greener electric bus transportation systems in India. ABB Power Grids’ business in India is responsible for planning, design, engineering installation and commissioning of the TOSA charging system under the MoU. Ashok Leyland will have the scope of manufacturing and supplying electrics buses compatible with TOSA technology.
ABB is also providing its ABB Ability Enterprise Asset Management (EAM) software solution for asset optimization, as well as its ABB Ability Network Manager Supervisory Control and Data Acquisition (SCADA) system to monitor and control the power network for charging stations and e-buses. On its part, AL will be providing vehicle, energy and EV related technical information using its iAlert Platform. This will further optimize maintenance processes, enable a fast response to fault incidents and better predict maintenance and performance needs. The overall solutions are equipped with remote access and 'cloud' capabilities and is scalable to meet future needs.