Wireless Charging: Futuristic or Futile?
This essay was written for a Composition and Rhetoric class
Wireless charging is a common feature in the latest cell phones, watches, and other gadgets. Instead of plugging a cord in, users simply place their device on a universal charging mat. Modern electric vehicles are also rechargeable gadgets that need to be consumer-friendly, which has led to automakers experimenting with wireless charging. Despite the concept being over a century old, an official standard for wirelessly charging vehicles was only recently released in October 2020 (SAE). DC charging—the current state of the art—has spent years dealing with growing pains from competing standards. Is wireless charging technology worth considering when tens of thousands of adequate charging stations already exist?
A brief technical background is necessary to understand the basic properties of wireless charging. The key principle is electromagnetic induction, a force that allows power to flow magnetically between two coiled wires that are not touching. In practice, a coil of wire is designed to create a magnetic field when power flows through it, and another coil is designed to easily receive that magnetic field. Wrapping both coils around a block of iron helps conduct the magnetic field more efficiently. In 1891, Nikola Tesla discovered a method to remove the iron and efficiently transfer power through the air between two coiled wires. Modern wireless chargers use induction to transfer power between a coil in the charging pad and a coil in the device. In comparison, wired charging can be called conductive because electricity is conducted between two wires. Wireless charging is based on an inductive transfer of power through air, while wired charging is conductive between two cables.
Ease of use is prominent among several benefits of wireless power transfer (WPT), but the high demands of an automotive application require careful consideration. Such a system needs to be safe, easy to use, and capable of transferring enough power for most use cases. J2954 (SAE’s new standard) uses a charging pad in the car, and one on the ground; the user just parks their car over the pad to begin charging. The system can transfer up to 11kW, which is higher than many AC charging stations (Electric Car Forums). Efficiency is 94% in a best-case scenario, and the car must be parked directly over the pad with less than 3 inches of misalignment (SAE 5). Toyota demonstrated WPT for vehicles in 2014, including automatic parking to perfectly align with the charging pad (Toyota Motor 3). Safety is roughly equivalent for wired and wireless charging; both make it effectively impossible to receive a shock. Wireless charging for vehicles has demonstrated safety, efficacy, and simplicity comparable to normal wired charging.
Wired charging is currently the de-facto standard for vehicles. Its main advantage over wireless charging is efficiency; the typical wired charging station is more than 97% efficient (Energy 1), and efficiency does not depend on well-aligned parking. Because the charger physically connects to the car, damaged contacts in the cable could damage the vehicle’s charging port. Unlike WPT, wired charging supports DC fast charging: the battery can be charged at a very high rate regardless of the car’s electronic limitations. A Tesla DC charging station can transfer 250kW, or 22 times the maximum power of a standard wireless charger; more power can be safely transferred because wired charging does not create a significant magnetic field (Deng 10889). Tesla has also demonstrated automatic wired charging that leverages existing standards: a robotic arm that plugs a cable into the car.
Performance, ubiquity, and efficiency outweigh the inconvenience of wired charging for the consumer’s electric car. Wireless charging for vehicles has shown similar specifications to wired charging, but is not superior on every count. WPT is simple for drivers and can be automated with widely available technology, but its efficiency and power transfer rates are inferior to conductive charging. The performance is on par with some existing wired chargers; the limitations of WPT do not render it completely impractical. Wired chargers are more performant, but require a driver to manually plug their vehicle in. It is feasible to implement WPT for vehicle charging, but it will likely remain a limited luxury feature due to its limitations.
Deng, Qijun, et al. “Wired/Wireless Hybrid Charging System for Electrical Vehicles With Minimum Rated Power Requirement for DC Module.” IEEE Transactions on Vehicular Technology, vol. 69, no. 10, Oct. 2020, p. 10889. EBSCOhost, search.ebscohost.com/login.aspx?direct=true&db=edb&AN=146653610&site=eds-live.
Electric Vehicle Chargers | My Electric Car Forums. https://www.myelectriccarforums.com/electric-vehicle-charger/. Accessed 1 Dec. 2020.
“Measurement of Power Loss during Electric Vehicle Charging and Discharging.” Energy, vol. 127, May 2017, pp. 730–42. www.sciencedirect.com, doi:10.1016/j.energy.2017.03.015.
SAE Wireless Charging Standard for EVs. https://www.sae.org/site/news/2020/10/new-sae-wireless-charging-standard-is-ev-game-changer. Accessed 1 Dec. 2020. Toyota to Begin Wireless Vehicle Charging System Verification Testing | Toyota Motor Corporation Official Global Website. https://global.toyota/en/detail/651273. Accessed 1 Dec. 2020.
Last modified: 12/01/2020