Electric vehicles (EVs) are the popular and accepted replacement for fossil fuels which are limited in supply and cause excessive pollution. Bloomberg NEF EVs Outlook forecast claims that EVs will become the majority of new car sales worldwide by 2040, accounting for 34 percent of all passenger cars on the road.
The effective charging of EVs is generally a big challenge, thus finding a suitable solution is a challenging task for researchers. Wireless EV charging is the latest fast-growing technology that could be a turning point for the EV industry. This charging system positions the energy source on the floor and its power receiver is mounted at the bottom of the car. The wireless chargers use the induction principle where the energy is transferred between coils via an air gap. Basically, the two coils form the power transformer which allows the energy to transfer. Energy can be transferred through any non-metallic surface.
The coils need to be in just the right position so that the charging process can begin. The principle is the same as with phone wireless chargers but with much more demanding requirements—significantly larger area, air gap, and higher energy.
Since the EV application requires greater distances between the energy source and receiver coil, the EV wireless chargers use a magnetic resonance coupling-based charging principle. When the electricity flows through the coil, an oscillating magnetic field is created. The magnetic field also causes oscillation of electrons in a nearby coil, thereby transferring power wirelessly. The transfer efficiency is further enhanced if both coils are tuned to the same magnetic resonance frequency. The wireless EV chargers available on the market require an approximate four-inch air gap.
Charging time is the most important parameter for EV application. When using a recently-developed wireless charger, the charging time resulted in a satisfying 3.5 hours for the charged car’s 9.5 kWh battery.
The future of this technology lies in Dynamic Electric Vehicle Charging (DEVC) chargers that operate on the “charging while driving” principle. These chargers would be mounted into the road allowing vehicles to charge while driving. Qualcomm demonstrated the DEVC system mounted in a 100-meter-long test track that charged EVs dynamically at up to 20 kilowatts at 70 mph (source: Qualcomm). The DEVC system is capable of dynamically charging several vehicles at the same time.
The advantages of the DEVC system show the great potential for autonomous vehicles (which are not yet fully realized). The vehicles will be charged while driving, allowing robot drivers to avoid stopping at charging stations, thus resulting in increased efficiency. Since the batteries are continuously recharged, the battery size can be reduced, which also affects the weight and price of the vehicles.
However, this system also has its drawbacks, such as high energy loss. Researchers have to increase the efficiency above 90 percent. Also, another important aspect to consider is the safety and environmental interference—the wireless chargers can emit high-frequency electromagnetic fields.