Article by: Pachern Jansa (Asst.Prof.), School of Engineering, Sripatum University
The concept of Wireless Power Transfer (WPT) through electromagnetic coupling has existed on the pioneering work of Nikola Tesla (1891). Inductive (or wireless) charging (WC), is a method of charging batteries without the need for users to plug the vehicle/device into a charging point with a cable. Electric vehicle wireless charging (EVWC) technology operates on the principles of magnetic inductance and magnetic resonance by using an electromagnetic field transfers energy across a small gap between an EV and a charging pad as shown in Fig. 1.
There are a few major players in the EVWC field, including WiTricity, Qualcomm, Conductix-Wampfler, Bombardier, EVWireless, and Momentum Dynamics. WiTricity is a start-up in Watertown, MA that began at the Massachusetts Institute of Technology. Their commercialized EVWC technology involves receiver and transmitter charging pads that operate on WPT via strongly coupled magnetic resonances. The receiver pad attaches to the bottom of the car, and the transmitter pad stays on the garage floor or is embedded in a paved parking spot, as shown in Fig. 2(a). Qualcomm’s Halo group has developed stationary WC pads in collaboration with the University of Auckland. Their patented “Double D” magnetic polarized pads (Fig. 2(b)), are claimed to have a unique arrangement that delivers twice the power with a higher efficiency compared to circular pads (Fig. 2(c)). Conductix-Wampfler’s inductive WC system has already been operating in the electric buses in Torino, Italy for the past 10 years. Their system consists of a primary (stationary) side, which is installed on the road, and a secondary (vehicle) side. Bombardier’s PRIMOVE system addresses both the static and the dynamic charging needs of buses, cars, and even light rail systems.
Their system is currently being used in public transportation by buses in Braunschweig, Germany. EVWireless has developed EV wireless chargers that use pulse transmission nanocomposite magnetic coupling (PTNMC) technology, that can control to allow electrical energy to be supplied intermittently at high voltage and high frequency with great efficiency. Momentum Dynamics have developed software that would enable energy suppliers to collect money from those who use their system to charge their EVs. Momentum Dynamics’ systems are currently being implemented in select FedEx trucks from Smith EVs. HEVO Power is another company that is implementing static and dynamic WC zones. Their system uses a unique smartphone app that finds open parking zones and helps drivers align the power station on the ground with the receiver on their car. Table 1 summarizes commercialized EVWC technologies and their specifications.
Table 1: EVWC Companies
Electric vehicle wireless charging technology is continuing to be researched by international research institutes and universities such as Korea Advanced Institute of Science and Technology (KAIST), Utah State University, Oak Ridge National Laboratory (ORNL), University of Tokyo, University of Auckland, Setsunan University, Tokohu University, Saitama University and University of British Columbia. Table 2 contains a list of the above reviewed research work and the various specifications for each system developed.
Table 2: EVWC Research
EVWC technology is feasible to be applied with the electric vehicle and also be found that the efficiency of WC system is about 7-10% slightly lower than traditional wired charging. But it is clear that there are a few of currently commercially electric vehicles are equipped with wireless charging systems. Also, the charging station has to be developed to have a function of wireless charging system. The safety and regulation of WC systems are just starting to set up. In 2017, the Society of Automotive Engineers (SAE) released a wireless charging standard for EVs that allows for the transfer of up to 11kW of power3. And the China Electricity Council (CEC) ratified and published a set of national standards for electric vehicle wireless charging, which will be based on the magnetic resonance technology developed and patented by WiTricity4. EVWC technology is still in its infancy, it suffers from lack of standardization. The growth of WC technology is mainly related to the growth of EVs and the development in the infrastructure of charging station. However, it may promise to change the world of EVs for the better.
1 IRENA (2019), Innovation outlook: Smart charging for electric vehicles, International Renewable Energy Agency, Abu Dhabi.
2 Taylor M. Fisher et. all. (2014), Electric vehicle wireless charging technology: a state-of-the-art review of magnetic coupling systems, Wireless Power Transfer, 1(2), 87–96.
3 Pollution Probe and The Delphi Group (2018), Final project report : City of Toronto electric mobility strategy assessment phase, Retrieved from: https://www.toronto.ca/wp-content/uploads/2019/05/9685-EMS-Assessment-Phase-Final-Project-Report.pdf
4Mark Kane (2020), China To Introduce EV Wireless Charging Standard Based On WiTricity Technology, Retrieved from: https://insideevs.com/news/420700/china-ev-wireless-charging-standard-witricity-tech/