They may be facing extinction in the electric-transport revolution, but one benefit of cars with internal combustion engines is that they are easy and quick to refuel, so travelling a long way in one is rarely a problem. Not so for their successors. In the absence of universal standards, electric cars come with a variety of charging systems and different sorts of cables and sockets. Extended journeys therefore need careful planning to make sure that the battery is fully charged at the start and that compatible fast-charging stations are available en route.

在电力交通工具革命中,内燃机驱动型汽车可能正面临被淘汰的命运,但它的一个优点是补充燃料方便快捷,所以驾驶一辆汽车长途旅行没什么问题。但后继汽车不是这样,在缺少通用标准的情况下,电动汽车使用各种充电系统,电缆和插座也各不相同。因此,长途旅行需要周密的计划,出发前确保电池满电,途中有兼容的快速充电桩可用。

It would be much more convenient if electric cars could be recharged wirelessly. Some electric toothbrushes and other small devices, such as mobile phones, can already be topped up in this way using a process called electromagnetic induction. This employs an alternating mains current flowing through a coil to create a varying magnetic field, which then generates another current in a second coil placed alongside it according to principles elucidated in the 19th century by Michael Faraday. The device containing the second coil then converts the transmitted power into direct current, which is used to recharge a battery.

如果电动汽车可以无线充电就方便多了。有些电动牙刷和手机等小型设备已利用电磁感应原理实现了无线充电。根据19世纪迈克·法拉第阐明的原理,让交流电流经一个线圈产生交变磁场,邻近的次级线圈可产生另一股电流,包含次级线圈的设备再将传输的电能转化为直流电,从而为电池充电。



WiTricity is working with a number of carmakers and sold its first commercial system in 2018 to bmw, which fits it to some of its 530e hybrid cars. Alex Gruzen, WiTricity’s boss, expects further developments soon. He says the arrangement can transmit power from the grid to the car’s battery with an efficiency of up to 93%, which is similar to that achieved by a plug-in system. Nor does a car’s receiving coil have to be positioned directly above the charging pad on the ground—a useful feature of resonating coils being that they do not have to be so closely aligned to transmit power.

WiTricity正在与多家汽车制造商合作,2018年将首款商用系统出售给了宝马公司,后者在部分530e混合动力车上使用了该装置。WiTricity公司总裁亚历克斯·格鲁泽期待不久将有更大的进展。他表示该装置能使电网向汽车电池输送电能的效率达到93%,接近插电式充电装置的效率。汽车的接收线圈不必放置在地面充电垫的正上方,这种线圈共振特性很有用,因为两者不必对齐就能传输电能。

As to how much power can be transferred, and how quickly, this is a question of cost and design. For most uses at home, a wireless charger of 11 kilowatts might suffice. That would provide around 50km of range per hour of charging and cost around $2,000, says Mr Gruzen. At this price, he says, a wireless system would be competitive with plug-in home-charging units.

至于能传输多少电能,传输的速度有多快,这涉及到成本和设计问题。对于多数家用场景来说,11千瓦的无线充电装置够用了。格鲁泽先生表示,每充电一小时能让汽车行驶约50公里,成本约2000美元。相比插电式家用充电装置,无线充电装置的这个价位是有竞争力的。

Another advantage of wireless recharging is what Mr Gruzen calls “power snacking”. This is topping up the battery when a car is stationary for a short time. The company provides systems to recharge taxis in this way while they wait in line, and to do the same for electric buses at bus stops. It is also possible to charge vehicles while they are on the move. That might make sense in places where vehicles often queue up, such as at airports, but Mr Gruzen does not think digging up motorways to install a charging lane is a realistic proposition.

无线充电的另一个优势是格鲁泽先生所说的“电力快餐”,在汽车短暂停驶时为电池充满电。该公司提供的装置能以该方式为排队的出租车充电,为停靠在公交车站的电动公交车充电,甚至为行驶中的汽车充电,对于汽车经常排队的场所可能派上用场,比如机场。但格鲁泽先生认为,设法在高速公路上布置充电车道的设想不现实。


Wireless recharging of electric trucks is also coming. In February, a team led by Omer Onar at the Oak Ridge National Laboratory, in Tennessee, demonstrated a 20 kilowatt set-up that thus takes three hours to recharge the 60-kilowatt-hour battery pack in a hybrid ups delivery truck. The team have also developed a 120 kilowatt fast-charger, which Dr Onar says would be capable of wirelessly charging electric cars at a similar rate to a Tesla Supercharger, one of the fastest plug-in systems available.

电动货车的无线充电时代也即将到来。由美国田纳西州橡树岭国家实验室的奥默·奥纳带领的团队演示了一种20千瓦的充电装置,它为一台UPS混合动力货运车的60千瓦时蓄电池组充满电耗费3个小时。该团队还研发出一种120千瓦的快充装置,为电动汽车无线充电的速度堪比特斯拉的超级充电桩,后者是现有充电速度最快的插电式充电装置之一。