How Wireless Chargers For Electric Cars Work

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Cable-less charging of plug-in hybrids and EVs

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Wireless Charging for EV Cars

Wireless chargers for EV cars should greatly accelerate the mass adoption of electric vehicles. In fact, wireless charging for an EV car's battery in your garage overnight removes yet another perceived inconvenience of EV technology - having to use cumbersome cables to plug it in or trying to find electric car charging stations. And in a green car such as an electric vehicle, wireless charging is even more important than with a cellphone. We need every incentive we can get to make the process as easy and convenient as possible to popularize the revolutionary technology.

Eliminating the need to remember to plug in charging cables to shop around for the correct home EV chargers is an important step in the right direction. Parking over a wireless electric car charger or charging pad that is simply placed on the floor underneath the car to charge the battery automatically and without cables is a very important feature and selling point. It is expected that the wireless EV charging market will grow at a compound annual rate of over 41% from 2021 to 2028.

Wireless EV Charging BMW

How Does a Wireless Electric Car Charger Work?

On old EVs such as the '90s GM EV1 and Toyota RAV4 EV, the charging method was to insert an inductive charging paddle into a receptacle on the vehicle. However, induction charging can also be performed wirelessly. If an automaker mounts a compatible receiver pad to its vehicle, it can interact with the magnetic field created by a ground-based charging pad. This creates an electric current that is then used to charge the battery pack.

The types of wireless charging can roughly be reduced to four main technologies:

  • CWCS - capacitive wireless charging systems
  • IWC - inductive wireless charging system
  • PMWC - permanent-magnetic gear wireless charging system
  • RIWC - resonant-inductive wireless charging system
Vehicle Wireless Charging Jaguar
Wireless Charger For Car Nissan
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Why Cars With Wireless Charging are Still Rare

Traditionally, the wireless charging of electric vehicles had several disadvantages in comparison with direct charging, which is why cars with wireless charging have not reached the mass market yet. The charging rate was slower and relatively inefficient compared to direct charging, there was an extra expense to build the coils and drive electronics, and there was no common standard. There have been several trials, such as the BMW 530e, a plug-in hybrid BMW 5 Series model with 3.2-kW wireless charging technology, but these are not yet commercially commonplace. In the meantime, the best luxury cars for green motoring are hybrid vehicles such as the BMW 7 Series Hybrid and new electric cars such as the Tesla Model S, even if we still have to charge them via cables.

MIT's adoption of resonant inductive coupling in 2006 was a big step forward for commercial applications, allowing much larger amounts of power to be transmitted over several feet without radiation. But how efficient is wireless charging nowadays? Oak Ridge National Laboratory has achieved 92% power-transfer efficiency at 20 kW over an 11-inch air gap. It has demonstrated that 120-kW systems as well 270-kW systems will allow rapid wireless electric-car charging at over 95% power-transfer efficiency.

The Advantages of Wireless EV Charging

There are many advantages to wirelessly charging EVs and here are just a few:

  • It's hands-free. No intervention is necessary by a human. You simply park the vehicle over the car-charging pad and charging starts automatically, the parameters of which can be scheduled and controlled via a smartphone app.
  • It's safer. At very high power levels, it is safer for humans not to handle charging equipment. There is also a lower possibility of human error.
  • Allows power snacking. When installed in any place where EVs frequently park for short periods, the batteries can be topped up. Examples include electric taxis and buses charging while waiting for passengers to board.
  • The connections are protected. Because the connections are enclosed, there can be no oxidation or degradation of electronics, electrical connections, or contacts. There is also no physical connector that can wear out, especially with frequent, intermittent charging. There is no cable, socket, or connector that can be subject to wear and tear.
  • In-motion charging will be possible. A future possibility is dynamic, in-motion fast charging on appropriately equipped roadways.
Wireless Charging Pad For Car BMW

Conclusion

The mass adoption of wireless EV charging will be here sooner than you think. Companies such as BMW, Siemens, Hevo Power, WiTricity Corporation, and Bombardier Primove are currently developing wireless charging technology for both passenger cars and heavy vehicles. With it, reaching the elusive goal of a 15-minute wait for wireless EV charging might be just around the corner. The unit price will come down thanks to economies of scale and plugging in might become a thing of the past in our electric cars of the future.

FAQs

What are the applications for and advantages of in-motion wireless charging?

On suitably equipped roadways or highway lanes, EVs can charge while driving, reducing the impact on charging infrastructure and energy demand during peak times. A 200-kW system can quickly charge many vehicles at the same time on heavily traveled or congested roads, spreading the cost and load over many users and virtually eliminating range anxiety.

What is being done to curb stray electromagnetic emissions from wireless charging equipment?

Advanced shielding tech is used to contain excessive heat and emissions. Oak Ridge National Laboratory has already used aluminum and nanocrystalline materials to dampen emissions and this technology is already validated up to 50 kW.

What are the current safety standards for wireless charging technology?

Safety and performance limits for high-power wireless charging have been established by the SAE J2954 standard. Any wireless charging equipment that reaches the market will have to conform to local and international regulations on electromagnetic field exposure imposed by bodies such as the FCC.

How big would a high-power wireless charging pad have to be?

The Oak Ridge National Laboratory has already demonstrated a charging pad that is about the size of an extra-large pizza with a 300-kW charging capacity. The development of poly-phase coil coupling in charging pads has allowed for the creation of smaller coils with a far higher power density. Such a pad will, therefore, still be compact enough to easily park over, while delivering fast charging ability. The receiving coil on the vehicle is significantly smaller than the floor pad.

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