Is the wireless charging electric vehicle market really coming?

While there may be widespread recognition that electric vehicles are more environmentally friendly than gasoline or diesel cars, some consumers stubbornly refuse to make the switch, primarily because of cost. Of course, there are other factors as well. According to a McKinsey report, range anxiety and the lack of more suitable and efficient charging stations are also cited as factors affecting purchases. The report says that as electric vehicle prices continue to fall, these two factors may soon become more prominent.

So why is charging such a concern? First, it's a numbers game. In most major markets, there aren't enough public charging stations on the road. As a result, existing car owners who rely on charging at home and work are afraid to take long journeys.

At the same time, the lack of infrastructure gives potential future buyers a reason to choose conventional cars, so unless there is continued investment in public charging, the uptake of electric vehicles will remain limited in the near to medium term.

Why wireless charging?

The traditional approach is to add wired charging at home, work, or even on public roads, each of which has its own set of unique limitations.

Home charging isn’t feasible in residential areas without parking lots, as some workplaces don’t want to lay more wires, and some aren’t willing to invest in wired charging infrastructure, which is more expensive in dense urban areas.

Additionally, wired plug-in car charging has some shortcomings in public environments. Level 1 and 2 AC charging and Level 3 DC fast charging are required, and the recent global health crisis may lead to a greater public focus on the use of public infrastructure and a preference for contactless technology whenever possible.

This is where wireless charging can play an important role. It has the potential to provide a more flexible and cost-effective approach to electric vehicle mobility.

Figure 1: The wireless charging transmission process from the power grid to the transmitter and then to the receiver. Source: KEMET

By eliminating the need for wires and bulky upright power supplies, EV drivers can charge in more places. In addition, it provides an innovative technical solution to address public concerns about shared charging equipment.

How charging works

In terms of fixed infrastructure, there are two main technologies: transmitter (charging dock) and receiver (car). When the vehicle enters the charging area, the system starts and the AC voltage of the power source is converted to DC to charge the battery via wireless inductive power transfer.

In simple terms, a typical platform sees power converted by an AC/DC converter, with a power factor correction stage used to improve efficiency by converting the input current into a sinusoidal waveform that is in phase with the grid voltage, thereby improving the power factor.

The DC/AC inverter generates a high-frequency AC voltage of 80 kHz to 120 kHz. A compensation network is then used to improve system efficiency, and a resonant capacitor is used to reduce parasitic losses (Figure 2).

Figure 2 AC/DC leakage current sensors provide robust offset characteristics with temperature and current. Source: KEMET

The transmitter and receiver coils supported by ferrite plates are then used to enhance and guide magnetic coupling for wireless transmission. Meanwhile, on the receiving end, the high-frequency AC is converted into high-power and high-voltage DC, which is then connected to the battery. The battery management system (BMS) is used to provide power control and communication, and perform functions such as checking battery charge, ultimately achieving stable and safe operation.

If dynamic wireless charging equipment is placed under the road, this becomes a most flexible power transmission method, allowing vehicles to charge while driving. This innovative technical approach is feasible on almost any type of road and in any environmental conditions, and can eliminate the need for traditional charging infrastructure such as gas stations. It can also serve as a more convenient way to power electric municipal and public transportation vehicles, such as buses that run on the same route week in and week out.

In fact, in recent years, several companies have begun to provide wireless electric road systems. Israel's Electreon is one such organization. Its shared charging platform is based on coils placed under the road in the center of the lane, a receiver under the vehicle chassis, and a management and power unit that provides real-time communication with each vehicle and transmits energy from the grid to the basic charging facilities under the road. Electreon said that the installation speed of the coil can reach one kilometer per night, and the cost per kilometer is $160,000.

The company says the benefits of wireless road charging for cities and the environment are manifold, including the elimination of charging stations, reduced carbon emissions associated with electric fleets, and relatively low infrastructure costs. For bus operators and electric vehicle owners, the system will encourage the development of lighter models by minimizing the need for onboard batteries. Wireless technology will also end anxiety about range, providing an infrastructure that is well suited for future autonomous driving.

How to overcome difficulties

The components behind wireless charging systems are widely available and well understood. For example, KEMET can provide most of the related systems and components, including AC filtering devices, pulse snubbers, ferrite tiles, and capacitors (Figure 3).

Figure 3 KEMET offers a full range of products that support wireless charging. Source: KEMET

For stationary applications, plug-in charging has taken the lead, is widely adopted and widely accepted. Automakers are also investing billions of dollars in battery development, especially in energy density and size. For dynamic charging, the nature of existing road designs, future maintenance and total lifecycle costs need to be considered.

This is not to say that wireless charging won’t work. In some cases, such as as new cities and urban centers are designed and developed, it may become the most viable and cost-effective solution. Looking ahead, depending on the specific location and application, public charging infrastructure will most likely include a mix of traditional plug-in charging and wireless charging to better support the long-term adoption of electric vehicles.

DAVID ADEEB is a Senior Technical Marketing Engineer at KEMET Electronics.