Wireless charging for electric buses

As part of its $1.5 billion new terminal project at Kansas City International Airport (MCI), the Kansas City Department of Aviation has invested in a wireless inductive vehicle charging system of Momentum Dynamics Corporation.

Momentum powers all types of electric vehicles using modular platform technology for automatic vehicle charging. There is nothing to plug in. Inductive charging uses an inductive ground assembly and an inductive vehicle assembly. The floor assembly can be installed flush to the ground or surface mounted.

“We’re designing and building a new, modern terminal and we want to make sure its supporting infrastructure doesn’t detract from the design,” said Aaron Kaden, MCI Fleet Manager. “Inductive charging was not only an effective solution in terms of monetary outlay and ongoing costs, but it was the only system we found capable of delivering power without the traditional plug-in infrastructure. .”

With inductive charging, buses do not need to be taken out of service to charge them. Frequent additional recharges will be provided to MCI Economy Parking electric shuttles. Buses can remain in service along the seven-mile loop.

Two chargers will support the entire MCI parking lot of approximately 28 vehicles (buses). The 300 kW wireless inductive chargers will be located at the shuttle stops in the new terminal (just outside the baggage claim area). While waiting for passengers, bus drivers will park the buses on the inductive charging terminals and charging will start automatically within 5 seconds of applying the brake. Charging will end automatically when the bus leaves the pad.

“We have the first wireless charging installation at an international airport that we know of anywhere in the world,” said Kevin Fisher, Director of Truck Systems Electrification at Momentum.

Fisher described what types of vehicles could benefit from the technology at airports. On the land side, he said passenger vehicles, taxis, shuttles and buses could take advantage of this technology. On the airside, any ground support equipment with a compatible high voltage battery system could use the system which operates between 400 and 800 VDC.

“Generally what we promote is fewer chargers to charge more vehicles by deploying en-route or opportunity charging, and there are a lot of benefits to that,” he said. declared.

Wireless charging offers the opportunity to lower the total cost of ownership of charging infrastructure and helps facilitate high utilization of charging infrastructure, he said. “You can spread that capital cost over more vehicles and it also facilitates higher vehicle utilization that can benefit from this approach,” he said.

Another advantage of the inductive charging process is that it requires less space. “When you think of conductive charging with cords and plugs, they usually have the same power electronics package that we do,” Fisher said. “They also have a pedestal, with bollards around it to protect it, and then cords and a plug so you effectively reduce some of your parking capacity with the charging infrastructure. Our setup has an electrical and electronic cabinet and everything else is underground. In fact, we hope that future generations will take the power electronics cabinet and put it in the ground as well. »

THE CHARGING PROCESS

The charging process has two basic parts: an inductive mass charger and a corresponding vehicle assembly that will receive the inductive charge.

Fisher described, “Instead of cords and plugs, it’s a magnetic resonance inductive load from the ground socket to the vehicle socket. This requires modifying or upgrading the vehicle to include our vehicle assembly, which passively connects to the vehicle’s cooling system. We prefer to connect directly to the high voltage circuit in the battery management system. We are also deploying a direct CAN bus connection for the battery management system. This approach allows us to be independent of OEMs. We totally rely on the vehicle’s battery management system to request how much power and when. It relies totally on the BMS of the vehicle itself.

The number of pads included in a charger depends on the vehicle battery. A 300kW four-pad system, like MCI’s two, provides Level 3 DC fast charging. Level 3 is 24-300kW, which Fisher says means adding 75-1,200 miles autonomy and 30 to 40 minutes on a 60 kW battery.

Fisher said, “You hear about megawatt change that puts out a lot of power very quickly. The faster you push the power, the more damage the vehicle gets, and that’s not what it’s about.

A magazine is 600mm by 600mm, 65mm thick and weighs 70 pounds. “It’s the cornerstone of our modular setup and it’s 75kW,” he said. “The power is equivalent to that of a Tesla fast charger and is sufficient for most cars and light vans. When we need more power, we add a pad. We look at the composition of the fleet. Many fleets have light, medium and heavy vehicles involved, so we generally advocate a 300kW quad pad system from the start.

To determine the requirements of the charging system, the operational flow of vehicles is taken into account. “Airport shuttles usually run on a fairly set route and they only have to reload periodically,” he said. “So if you can tie that to the operation, dropping off passengers and picking up passengers, that’s usually a sufficient amount of charge and you can actually end up in a lot of cases putting in a smaller battery because you you don’t need the range on those short commuter type trips and it allows you to reduce the cost of the vehicle, reduce the weight and make it more efficient.

BUSES AT MCI

In 2017, the Kansas City Aviation Department became the first US airport operator to use all electric buses when it added four BYD buses to its fleet and three more in 2020.

Initially, MCI’s plan for inductive charging was to retrofit four existing BYD K7 30-foot electric buses with the wireless system to enable automatic battery charging. An MCI spokesperson said in September that option was being evaluated.

Jason Yan said MCI’s current buses do not have the wireless charging system installed. MCI will have 30-foot BYD K7M electric buses with a wireless charging system. The K7M can accommodate up to 22 people and has a short turning radius. The batteries are iron phosphate and have a 12-year warranty, and the battery capacity of the K7M bus is 215 kWh. With a fully charged battery, the K7M can travel up to 158 miles. The maximum acceptable charging power is 150 kW. Charging time is 1.5-2 hours with air charging or 2-2.5 hours with inductive charging. Yan clarified that the charging power of an overhead charging system is theoretically higher than that of a wireless charging system. But, he said for the K7M, due to its size, the maximum charging power and charging should be similar or about the same.

Yan noted that more and more airports are considering inductive charging.

The new MCI terminal will open in late February or early March 2023.

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