Wireless charging for EVs: All you need to know

EV charging

Wireless charging isn’t anything new, it has been around for a long time and we all have been using it in some way or the other. Almost all the latest phones, high-end earpods, and Apple i-watch, all have wireless charging features. When it comes to electric vehicles, it is not simple as it may sound. There are many possible ways to achieve this and one of them is through magnet coil pads placed on the ground. There is definitely a possibility to even achieve wireless charging on the go. The second scenario would be best suitable when we will have autonomous cars running on the road. As of today, it is also possible to retrofit existing EVs with such wireless charging capability. There are solutions available in the market right now that cost a couple of thousands to install.

How is Wireless Charging achieved?

It is as simple as the functioning of an induction stove but with a tweak. There is a transmitter and a receiver in the form of a coil. When an AC supply is given to this coil, it creates an electromagnetic field around the coil. This electromagnetic field then cuts whatever is in its vicinity. Now, if you place another coil in this electromagnetic field, it will induce power to the receiver coil which will then be converted to DC and fed to the battery via the battery management system (BMS).

Charging
Source: US Department of Energy

Wireless Charging Methods

There are multiple approaches to achieving wireless charging, two of the most talked about are explained below.

Inductive charging

When you pass the AC supply to the coil at a high frequency, the coil generates an electromagnetic field around it. The secondary coil must be placed in proximity as close as possible to intercept most flux (in simple words wireless power). The amount of power the secondary coil captures is directly proportional to its cross-section. If you want to achieve maximum efficiency, both coils have to be identical and should align parallelly. The efficiency boils down to the smallest distance between the coils.

The drawback of this system is that the flux drops rapidly as we separate the coils. Beyond a few centimeters, the flux becomes so weak that the system is no longer able to induce power to the secondary coil.

Resonance charging

Resonance charging is a form of inductive charging in way that the magnetic field generated by one coil induces a current in a second but here, it takes advantage of strong coupling between the two even if they are separated by a few centimeters. The principle here is to send energy tunnels instead of sending flux in the Omni direction. The secondary coil needs to have a large cross-sectional area to absorb more energy. This method enables the ability to transfer power to multiple secondary coils.

The drawback here is that the method is not efficient due to power leakage. It suffers from electromagnetic field interference as well.

We spoke about what are the different types of wireless charging available. Now, let’s talk about different ways to implement wireless charging for electric vehicles.

Wireless charging implementation

Based on the application, wireless charging for EVs can be classified into two categories

Static Wireless Charging

Static wireless charging has multiple use cases. The basic principle here is that the vehicle gets charged when it is static. The transmitter is fixed on the ground and the receiver is integrated into the vehicle underneath. When the vehicle aligns the receiver over the transmitter, the system become activated and starts charging your vehicle. The charging speed depends upon the size of the coil and the distance between the transmitter and the receiver. This type of charging is best suited in parking lots, garages, office premises etc.

Dynamic Wireless Charging (Charging on the go)

As the name suggests, dynamic wireless charging or charging on the go method is used when the vehicle is in motion. The power is transferred over the air from a stationary transmitter to the vehicle where receiving coil interferes with the magnetic power and charges the vehicle. This is possible with charging pads integrated along the roads. Though the system is not the best when it comes to efficiency, however, it is the most convenient way to charge your vehicle. It also eliminated the range anxiety and need for heavy energy storage in the vehicle.

Challenges

  • As of today, when we say retro-fitment, we need to take care of the space requirement for the magnetic coil in the vehicle.
  • All the safety aspect has to be taken care of while integrating this technology into the vehicle.
  • Mechanism to determine any external interferences (living or a foreign object)
  • Efficiency is another issue when we talk about wireless technology. Though it is convenient, it is not the most efficient when compared to wired charging.
  • The magnetic interferences need to be analysed and regulated for any direct or indirect influence on human as well as animal health.
  • Infrastructure needs to be put in place which would require a lot of investments.

Conclusion

Inductive wireless charging relies on relatively low-frequency oscillating field power transfer. The technology is simple and has reached a level of maturity. We also see this form of wireless charging in our everyday use as well. Inductive wireless charging is good if you are looking to charge a single device in an efficient way.

On the other hand, resonant wireless charging relies on high-frequency oscillating magnetic field power transfer. The technology is more complex than the inductive method and still in the exploratory phase in the sense that the system is less efficient.  This technology would be a good fit for those who are looking for practicality over efficiency.  

Wireless charging will definitely eliminate the range anxiety and help buyers consider EVs over any other vehicle. However, automakers are also working on Fuel Cell Vehicles which are EV alternatives. The fuel cell vehicles use hydrogen as a fuel to generate electricity on the go instead of storing it in the battery. Both of these options are aiming toward achieving the ultimate goal of using clean energy for transportation and making the planet earn green again.

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