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28 it is power-hungry and demands up to half the battery’s power under extreme conditions. That had to be taken into account when specifying the battery pack. Batteries and opportunism Akasol supplies the 36.8 kWh battery pack and battery management system. The pack consists of two 18.4 kWh modules connected in series. The lithium-ion chemistry on which the battery is based is lithium nickel manganese cobalt oxide, also known as NMC, which supports the very high currents needed for rapid ‘opportunity’ charging during day-to-day operations. The third-generation shuttle exploits this by charging at selected stops, a strategy that supports the goal of a transport system intended to maximise the number of passengers carried per hour in each direction while keeping the number of vehicles required to achieve this to a minimum, van der Zwaan explains. Charging at a rate of 4C – that is, using a current four times the battery’s rated capacity in Amp-hours – a discharged pack can take a full charge in 11 minutes, he says. “You never stop for that long, but if you have a dwell time of 1 or 2 minutes at stations at the end of the line you can still give it a considerable boost.” The battery sends its power to an inverter that drives a single AC motor mounted in the centre of the chassis, which drives a differential in the front axle. The high-capacity contact charging equipment is supplied by AEP. The system features plates embedded in the ground at the stops, over which the vehicle positions itself before lowering its contact pads. “We were using contact charging for the second generation, then inductive charging became available. That is still a relatively new technology and its efficiency is lower, so it can’t do the 4C that opportunity charging needs,” van der Zwaan adds. “The navigation technology’s centimetric precision is also essential for opportunity charging,” he says. “In operation, we give the shuttle orders to pick up and set down passengers and, depending on the battery’s state of charge, to recharge itself as well. So the whole charging system is automated.” Lohmann emphasises that opportunity charging provides a significant commercial advantage in comparison with the principal alternative of overnight charging, particularly when used with a vehicle that has a larger passenger capacity. With the conventional approach, a vehicle will be in operation for 8 hours, followed by 6 to 8 hours on charge. By charging whenever they get the opportunity, 2getthere’s shuttles achieve about 90% availability, while competitor vehicles manage about 50-60%. “We require only one-third the number of vehicles for a given transport system capacity,” Lohmann says. Towards mixed operations While sticking with Level 4 autonomy, 2getthere is working to ease the restrictions on the ODDs, gradually stepping into more complex scenarios. The industry has already demonstrated the safety of Level 4 autonomous vehicles in fully segregated environments – private roads on which no other traffic is expected – Lohmann stresses. He adds that Rivium was the first segregated lane application to add an interface with the public road at crossings with the second-generation vehicles. This required control of the crossings and other measures to mitigate all the potential hazards. The next step, still at Level 4, is to mix with vehicles on the October/November 2020 | Unmanned Systems Technology Dossier | 2getthere third-generation shuttle The inverter supports normal driving under battery power and regenerative braking, the primary means of slowing the vehicle In operation, we give the shuttle orders to pick up and set down passengers and, depending on the state of charge, to recharge itself automatically as well