Could Wireless EV Charging Shift to the Fast Lane?May 12, 2021 by Ikimi .O
Will making the jump to EVs push wireless charging to the next level?
Imagine getting your electric vehicle (EV) charged while in transit or parked without having to keep it plugged in. Last year, the Society of Automotive Engineers (SAE) published the SAE J2954 standard to fast-track wireless EV charging adoption. With this advancement and fueled by recent research, could EV wireless charging be on the horizon in the near future? Will today's recent focus on EVs be the push needed to propel wireless charging to an everyday method to charge your electric vehicle?
An example of a wireless charging system. Image used courtesy of HEVO
Before digging into wireless EV charging, it is essential to understand the overall mechanics and current ways of implementing this technology.
How Does Wireless EV Charging Work?
Wireless power transfer (WPT) was first discovered by Nikola Tesla. Over time with innovation, current applications for WPT include wireless charging of devices like cellphones and, more recently, electric vehicles.
The general principle of wireless EV charging. Image used courtesy of Ahmad et al
WPT in the automotive sector is based on the power transfer principle between a transmitter and a receiver. The transmitter is part of a ground assembly (GA) and sources its power from the grid, while the receiver is part of the vehicle assembly (VA) which receives the AC and converts it to DC to charge the EV's battery.
Though the concept and mechanics of WPT are generally understood, WPT can be beneficial in all types of applications, from industrial to consumer tech. These benefits are what keeps the ball rolling towards wireless EV charging.
Is Wireless Charging Beneficial to EVs?
According to WiTricity, wireless EV charging is as efficient as conventional plug-in charging, having up to 93% efficiency, with 3.6 to over 11 kW charge levels and a level 2 charging type. The technology also offers a single GA design suitable for sedans, SUVs, and sports cars. It also ensures seamless wireless power transfer by utilizing various materials, including asphalt, snow, and cement.
Recent research on this technology investigates efficient ways to achieve wireless EV charging. For example, Cornell's notable 13.56 Mhz high-frequency work was conducted by Prof Khurram Afridi and his team.
Cornell research team and their WPT system. Image used courtesy of John Munson and Cornell University
Their design incorporated an active variable reactance (AVR) rectifier that allows EVs to obtain full power when passing overcharging plates that are not perfectly aligned and efficiently transfers power to larger vehicles with a comparatively wider air gap.
With its additional time-saving capabilities, WPT, and wireless charging overall, could help increase warehouse productivity and eliminate the need for costly, bulky, and wear-prone cables and connectors, thus expediting the evolution to exclusively electrified transportation.
Through both academic and company pursuits, it becomes likely that there is a growing interest in establishing this technology. At the moment, there are two main ways of wirelessly charging an EV.
Methods for Wireless EV Charging
Although magnetic resonance is the preferred method for WPT, another promising technique for wireless EV charging is capacitive coupling.
Magnetic resonance applies resonant coupling to achieve WPT. According to WiTricity, when two systems' natural frequencies are identical, they achieve resonant coupling. This principle is also used to achieve WPT and, ultimately, wireless EV charging, where the two systems are the GA and VA. It is efficient and allows a considerable charging distance.
Image of magnetic resonance wireless EV charging system. Image used courtesy of Qiu et al
The capacitive coupling method, on the other hand, achieves WPT by utilizing conductive plate couplers. Dr. Brandon Regensburger's research on "Capacitive Wireless Power Transfer Systems for Electric Vehicle Charging" extensively explains how this method achieves compact, high-frequency wireless EV charging.
An example capacitive WPT system implementation. Image used courtesy of Brandon Regensburger
His approach involves using two pairs of capacitively coupled plates (one in the road and one under the vehicle) and an inverter that converts the DC input voltage to high-frequency AC voltage (which is stepped to a high level because of a matching network). The high voltage from the coupling plate in the road then transfers power between the air gap between the plates. Once the voltage moves to the vehicle, the voltage is stepped down with a matching network to charge the EV's battery.
Methods such as this are helping to prove the ability to wirelessly charge EVs. However, how likely is it to become mainstream and be implemented on a larger scale?
Possibilities and Considerations
The US Department of Energy (DoE) states that wireless power transfer coupled with lower costs and enabling policies could increase the likelihood of full implementation in the future. This could be especially true with the latest advances in WPT replace magnetic fields with electrical fields. The absence of ferrite materials that would otherwise guide the magnetic fields makes the system lighter, smaller, more cost-effective, and easier to incorporate on roadways. Although electric fields generated by readily available voltage tend to be weak, boosting the system achieves sufficient power transfer levels.
Besides technical innovation, suitable government policies can enable the full implementation of WPT in the transport sector. If this happens, the most effective approach would be to electrify the world's busiest roads. Consequently, WPT would be able to supply large, long-haul trucks with power. Another viable strategy would be to install charging strips in busy cities, from traffic lights to parking lots. Knowing that governments give incentives and subsidies to charging stations could encourage investment from private, public, and commercial sources. For example, installing a conventional plug-in charging station in your garage saves the cost of running your EV as more than 80% of all charging is done at home.
Since there is a global focus zooming in on EVs, there is an increased chance to see more interest and investments in wireless charging for EVs, both commercially and academically. The implementation scale in size will vary and depend on the future shape of the EV industry and the technology that could make it happen.
Featured image used courtesy of WiTricity
What are your thoughts on WPT and wireless EV charging? Is this something we could be seeing more of in the near future? Have you ever worked with WPT? What has your experience been? Let us know in the comments down below.