No cables, no problems

This article originally appeared in the April'23 magazine issue of Electronic Specifier Design – see ES's Magazine Archives for more featured publications.

Inductive charging, using 30kHz to 30MHz time varying magnetic fields is the most common method of wireless power transfer (WPT). These frequencies are impervious to air, water, ice, concrete, wood, plastics, and other common non-metallic materials and too low to damage DNA or cells.

Safety first

In IDTechEX’s report, Wireless Charging Market for Electric Vehicles 2023-2033, the analyst explains that the vehicle still has to be shielded for charging to avoid the magnetic field interfering with vehicle systems, heat the battery or circulate current in metallic parts.

Ferrites can be used for shielding to direct the magnetic flux, or aluminium plates can be used in the charging design, to minimise current leakage.

HATC AND MOJO MOBILITY BASED A WIRELESS CHARGING SYSTEM ON THE KIA SOUL EV. (PICTURED -THE URBAN EDITION. SOURCE: KIA)

For the report, IDTechEx interviewed various players in the industry and found that shielding is mainly added under the transmitter pad and above the receiver pad. The preferred method was to recycle the magnetic field and contain it within the pads, rather than radiating electromagnetic fields to produce resonant, highly coupled, shaped magnetic fields.

There are also foreign object detection (FOD) and living object protection (LOP) systems to identify any metallic objects caught between the transmitting and receiving pads and suspend power transfer to avoid the metal heating up and potentially burning other materials.

Capacitive sensors in the pad can monitor the performance of the coils and any changes of capacitance brought about by the presence of a metal object. It may not detect organic objects, however, such as an animal on the pad, pointed out IDTechEx. Optical sensors around the edge of the plate using infrared LEDs, photodiode detectors or lidar can be used to detect both metal and organic objects on the pad and, when they are detected, switch off the charging process.

A wireless charging system requires a wall box, and two other elements. The first is the ground assembly, where AC mains electricity is converted to DC using rectifiers and then converted to high frequency AC using inverters. For the vehicle assembly, a secondary rectifier converts the transmitted AC into DC to power the vehicle battery. IDTechEx estimates that about 70% of the cost is associated with the ground assembly. 

Components for charging

Charging companies, like Qualcomm and Sprint Power, are developing charging pads and BMW has introduced static wireless charging systems. Hyundai-Kia America Technical Center (HATCI) and Mojo Mobility (Mojo) jointly developed a wireless charging system for the Kia Soul EV, but so far, there are no plans to bring this model to production.

Transfer efficiency for wireless charging is around 90% to 93% which means a bus battery can be topped up in 10 minutes there is little data, however, on how fast WPT charges non-commercial vehicles in a domestic setting or if it will be powerful enough to charge all types of vehicle.

The cost of the WPT charging pads may be the major obstacle. Estimated cost for full scale production is $5,000-$7,500 which far exceeds the typical cost of £695-£1,395 for home EV chargers.

According to IDTechEx, wireless EV charging will play a key role in developing the overall network of EV charging infrastructure alongside Level 1 and 2 AC charging and Level 3 DC fast charging. Development is likely to be divided between low cost, low power chargers (i.e., less than 22kW) for convenience charging applications and more powerful equipment for opportunity charging. 

The report says that companies like Hyundai and China’s FAW and BYD automotive manufacturers, are already offering factory-fitted wireless charging hardware from key players on select vehicle models. The analyst also expects costs for static wireless charging units to decrease with larger volumes being manufactured from 2025.

Israeli company, Electreon is developing and testing wireless charging embedded in roadways, for charging while driving. This could mean smaller batteries to reduce the weight in the vehicle but adapting the road infrastructure will be expensive, particularly when the percentage of vehicles able to benefit is so small, says IDTechEx. Despite that, there are demonstrations underway today, in Sweden, Germany, France, and Italy, to electrify thousands of km of roadways, adds the report.

Figure 1. Categories of FOD methods used in wireless EV charging systems. Source: IDTechEx