Wireless charging for EVs could aid adoption

While there might be widespread recognition of the greener nature of electric vehicles (EVs) compared to petrol or diesel vehicles, some consumers stubbornly refuse to make the transition, primarily because of cost. However, other factors also come into play. According to a McKinsey report, range anxiety and not having enough access to efficient charging stations are also recognized as severe barriers to purchase. As the price of EVs continues to decline, these two factors could soon take an even greater prominence, according to the report.

So, why is charging such a big concern? Well, primarily, it is a numbers game. In most major markets, there are not enough public charging stations on the roads. The result is that existing owners, who often rely mainly on home and workplace charging, are fearful of undertaking longer journeys.

Meanwhile, this lack of infrastructure gives potential future buyers a significant reason to remain loyal to traditional powertrains. So, unless public charging provision sees sustained investment, the uptake of EVs is likely to remain constrained over the near-to-medium term.

Why wireless charging?

One solution could be the introduction of a more dynamic and flexible approach to electric-car charging, which traditionally has been based on wired plug-in charging at home, at work, and on public roads. Each of these approaches comes with its own set of particular limitations.

Home charging isn’t always possible where dwellings do not have parking garages, as it is not desirable to drape wires across pavements from house to road. Some workplaces are unwilling to invest in wired charging infrastructure, while space for such infrastructure is often at a premium in dense urban areas.

Then there are the shortcomings in the way that wired plug-in car charging takes place in public environments. Both level 1 and level 2 AC charging and level 3 DC fast charging are all ‘hands-on’ techniques, in that they require the driver to play a physical role in the beginning and end of the charging process. The recent global health crisis is likely to result in more significant public concern around the use of communal infrastructure, with an emerging preference for contactless technology wherever possible.

This is where wireless charging could have a significant role to play. Typically based on the ability to charge batteries by transmitting electromagnetic waves from a charging pad to a plate attached to a vehicle, wireless charging holds the potential to deliver a more flexible and cost-effective approach to EV mobility (Figure 1).

Figure 1 The wireless power transfer process goes from the grid, to the transmitter, through to the receiver. Source: KEMET

By eliminating the need for wires and bulky upright power units, EV drivers could recharge in a far greater number of locations. Furthermore, it also provides an innovative technological answer to any public health fears around the sharing of charging equipment.

Power transfer explained

In terms of stationary infrastructure, there are two primary technologies—the transmitter (charging stand) and the receiver (car). The system is activated when the vehicle enters the charging area, with AC voltage from the mains converted into DC to charge the battery, supported by a wireless induction power transfer.

In simple operational terms, a typical platform would see the power from the mains converted by an AC/DC converter, with a power factor correction stage used to increase the efficiency by transforming the input current close to a sinusoidal waveform that is in phase with the grid voltage, therefore improving power factor.

A DC/AC inverter creates a high-frequency AC voltage of 80 kHz to 120 kHz. Compensation networks are then used to improve system efficiency using a resonant capacitor to reduce additional losses (Figure 2).

Figure 2 An AC/DC leakage current sensor offers robust offset characteristics with temperature and current. Source: KEMET

Then sender and receiver coils, supported by ferrite plates, are used to enhance and direct the magnetic coupling for wireless transfer. Meanwhile, on the receiver side, high-frequency AC is converted to high power and high voltage DC and then connected to the battery. A battery management system (BMS) is used to provide power control and communication, and to perform functions such as checking the battery level, ultimately enabling stable and safe operation.

Taken to its extreme, dynamic wireless charging—where coils placed under the road connect with a receiver located under the vehicle chassis—could become an even more flexible approach to power transfer, allowing vehicles to pick up charge on-the-go. Such an innovative technological approach, which is feasible on almost any type of road and under any sort of environmental conditions, could remove the need for traditional charging infrastructure, such as gas stations. It could also act as an elegant yet robust approach to the powering of electric municipal and public transport vehicles, such as buses that operate on the same routes, week-in, week-out.

Indeed, in recent years, several companies have emerged to offer wireless electric road systems. One such organization is Israel-based Electreon, whose shared charging platform is based on copper coils placed under the road at the center of the traffic lane, a receiver located under the vehicle chassis, and a management and power unit that provides real-time communication with each vehicle and transmits the energy from the grid to the infrastructure under the road. Electreon says that the copper coils could be installed along a kilometer of road in one night at the cost of $160,000 per km.

The benefits for the city and environment are numerous, the company says, and include the elimination of charging stations, the reduction of carbon emissions associated with an electric fleet, and relatively-low infrastructure costs. For bus operators and EV owners, the system would encourage the development of a lighter vehicle fleet by minimizing the requirement for an on-board battery. The wireless technology would also bring an end to range anxiety while delivering an infrastructure that—in the future—will be ideally suited for the adoption of autonomous vehicles.

Overcoming barriers to adoption

Broadly speaking, reticence toward the adoption of EVs is not related to technological barriers. The components behind wireless-charging systems are widely available and well understood. KEMET, for instance, can offer most of the associated systems and components—including AC filtering devices, pulse snubbers, ferrite tiles, and capacitors (Figure 3).

Figure 3 KEMET offers a full range of products to support the wireless transfer process. Source: KEMET

The biggest challenge to adoption is resistance to change. For stationary applications, plug-in charging has stolen a lead over wireless and is widely adopted and well understood. Carmakers have also invested billions of dollars into battery development, focusing particularly on energy density and size. For dynamic charging, there are considerations around the nature of existing road designs, future maintenance, and whole life costs.

That is not to say that wireless charging does not have a role to play. In some circumstances, such as with the design and development of new cities and urban centers, it could emerge as the most viable and cost-effective solution. Going forward, depending on the specifics of individual location and application, public charging infrastructure is most likely to comprise a mix of traditional plug-in charging and wireless charging to better support the long-term adoption of EVs.

Whatever the mix, component suppliers like KEMET are well-positioned to support what has become a fast-developing and technologically-innovative market. The trend to the electrification of the vehicle fleet is unstoppable and the pressure is on national governments and local authorities to develop sufficient charging infrastructure to meet demand.

David Adeeb is senior technical marketing engineer at KEMET Electronics Corp.

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