Talking about the solution of wireless charging technology for electric vehicles

In a world where EV charging is a key point in facilitating the energy transition, other solutions can go hand in hand with electric charging stations. One such solution is wireless charging. Wireless car charging is an enhanced version of smartphone charging with several differences. “Wireless inductive charging enables electric vehicles[EV]Automatic charging without the need for cables,” Plugless Power CEO Michael Rai Anderson said in an interview with Power Electronics News.

Author: Maurizio Di Paolo Emi

In a world where EV charging is a key point in facilitating the energy transition, other solutions can go hand in hand with electric charging stations. One such solution is wireless charging. Wireless car charging is an enhanced version of smartphone charging with several differences. “Wireless inductive charging enables electric vehicles[EV]Automatic charging without the need for cables,” Plugless Power CEO Michael Rai Anderson said in an interview with Power Electronics News.

“Technically, everything is scalable; however, as power delivery rates increase, so must the complexity and size of the power management electronics.” “More importantly, as power goes up, so does the Consider many other factors, such as heat loss and thermal management. The higher the inefficiency, the higher the power, the greater the heat loss, and the more that has to be done to manage that heat.”

Dr Milan Rosina, principal analyst for power electronics and batteries at Yole Développement (Yole), said EV charging requires higher voltages, power and more energy transfer. As a result, the technical, safety, cost and environmental challenges are even more severe. “While wireless chargers and smartphones are often in close contact, it is difficult to precisely position the vehicle over the charger, and the distance between the charger (transmitter) and the receiver mounted on the vehicle is significantly greater,” he said. many.”

This leads to inefficiencies in energy transfer under practical conditions, Rosina points out. However, high efficiency is required to reduce cost and thermal management challenges and reduce the environmental impact of wireless charging (Figure 1).

In addition, the high voltage and power required for EV charging pose additional challenges to the safety and cost of wireless charging systems. “Wireless charging also requires the integration of additional chargers into the vehicle, which increases the cost of the vehicle,” Rosina said. “Installing EV wireless chargers in public places also presents many challenges. Compared with wired chargers, the new generation of wireless charging The upgrade of the car is more complicated. Autonomous charging is often seen as a convenient or even automatic charging method. It is true that self-driving cars will best use an automatic charging function, and wireless charging seems to be a promising option. But Several companies have also developed automated solutions, such as battery replacement, robotic arm charging, or automated mobile charging systems. Once the demand for automated solutions is urgent, such solutions will compete with wireless charging.”

Talking about the solution of wireless charging technology for electric vehicles
Figure 1: The wireless charging challenge (Source: Yole Développement)

Andy Wilson, business development director at UnitedSiC, believes that the earliest adopters of wireless charging will be commercial vehicles (buses, vans, taxis), who want to expand their vehicles with wireless charging as a way to quickly supplement charging Scope. “These supplemental charging events occur during short periods of time when the vehicle is parked at a regular rest point,” he said. “This dynamic approach will require a higher level of power transfer than in residential wireless charging, where charging It can be done overnight at a much lower power level.

“To be able to meet the high power requirements of commercial supplementary charging, resonant magnetic induction must occur at relatively high frequencies, which requires faster switching devices,” he added. “These requirements take full advantage of the wide band gap.[WBG]Advantages of semiconductor devices. “

Some wireless charging systems claim to deliver up to 20 kW with up to 94 percent efficiency from plug to battery, according to Ali Husain, marketing and strategy manager at ON Semiconductor. “The resonant frequency is typically as high as 100 kHz, so fast switching of the WBG is suitable for these systems,” he said.

Electric Vehicle Charging Solutions

When it comes to electric vehicles, there are multiple ways to “refill” the car with energy, including battery charging, battery swapping, and hydrogenation (Figure 2). Rosina pointed out that hydrogen refueling is used in hydrogen fuel cell electric vehicles, which represent only a small portion of the electric vehicle market. In the case of battery replacement, using a combination of computer vision and wireless communication, the workstation can identify the exact location of each battery module to be replaced. We cover this topic in more depth here at EE Times.

Talking about the solution of wireless charging technology for electric vehicles
Figure 2: How to recharge an electric car (Credit: Yole Développement)

“Electrification of fleets has become mandatory in order to meet the government’s stringent CO2 reduction targets,” Rosina said. “While there are varying degrees of electrification, it is only through ‘strong electrification’ in EVs and PHEVs. ‘ to achieve the necessary emissions reductions.”

Talking about the solution of wireless charging technology for electric vehicles
Figure 3: EV/HEV classification (Source: Yole Développement)

Conductive charging via cable involves manually connecting conductors between the charging station and the vehicle. Depending on the size of the cable, current flows through this wired connection, allowing for a high charging capacity. The main advantages of this charging method are:

• Reduce infrastructure costs
• High power transfer efficiency
• Possibility of high-speed charging (but increased cost)
• Low maintenance requirements
• Virtually no electromagnetic radiation

The main disadvantages of this charging method are:

Requires human intervention to address the associated shortcomings of not having an automated process

Cables take up space in the parking area

Due to all the advantages listed above, conductive charging will certainly continue to be used in all-electric vehicles for many years to come. According to Yole Développement’s “DC Charging for Plug-In Electric Vehicles 2021” report, the DC charger market will grow at a CAGR of 15.6% through 2020, reaching approximately 440,000 units by 2026. It is very likely that we will also see systems with different types of automation associated with this technology in the near future.

“Wireless charging solutions are still in their infancy and face many challenges,” Rosina said. “A ‘rope’ or ‘wire’ charging solution will remain the mainstream charging solution for electric vehicles for the foreseeable future. The challenges associated with transmitting very high currents through charging cables and connectors have led to the development of a pantograph solution – mainly for electric bus charging.”

Wilson noted that wireless charging requires infrastructure investment (transmitter pads) and vehicle investment (receiver pads). “For commercial vehicles whose schedules require more than the vehicle’s battery capacity, being able to receive supplemental charges throughout the day during routine stops can bridge the gap,” he said. “This range extension value provides the business case for supporting wireless The investment required for charging is reasonable. For private passenger vehicles, the primary value of wireless charging is convenience. For most of the population, they are willing to invest relatively little for the convenience factor. Therefore, we believe that addressing this In the market, the cost must be greatly reduced.”

Anderson noted that current methods are based on wired charging devices, “but such devices are not practical in the long term because they inherently pose a trip hazard, are prone to damage, and require the driver to have the vehicle plugged in even in the presence of weather: bad.

“Historical R&D in wireless inductive charging technology has focused on transmit and receive coils; however, current R&D efforts are more focused on communications, user interfaces and sensory arrays,” he added.

The security challenges associated with wireless charging are no different than those associated with wired charging. Similar software protocols and encryption are required to provide system security. For a given power output (ie 3.3 kW, 7.2 kW, 11 kW), the charging times will be relatively similar, Anderson said.

From an electric autonomous vehicle perspective, the first challenge to implementing wireless charging in cars is through the adoption of common standards. “Now, SAE has published its first set of standards[2020年10月], we took the first steps toward this standard,” Anderson said. “Now, we need consumers to demand the convenience and value proposition that wireless charging can provide to ensure EV OEMs begin to adopt wireless-ready or have wireless functional electric car. However, it should be noted that wireless charging enables autonomy. In fact, it is well known that driverless autonomy would not be possible without wireless charging technology. “

The SAE J2954 and SAE J2846/7 standards published by SAE International have set standards to regulate energy exchange capable of charging up to 11 kW with up to 94% efficiency and a board-to-board distance of up to 25 cm. The same system can be applied to autonomous infrastructure designed for cars that can park and recharge themselves.

Technology

The first theoretical basis for “wireless” power transfer was Nicola Tesla (1896). Its working principle is similar to that of a transformer, and its working principle is based on the law of magnetic induction. A primary circuit called a transmitter produces a time-varying magnetic field. The secondary circuit receives this field, called the receiver, which is connected to the device to be powered. Of course, the most important parameter to consider is the distance between the two circuits and their alignment. Poor alignment and relatively large distances degrade performance and make energy transfer inefficient.

Magnetic induction charging uses an energy exchange between two pads, one on the ground and the other under the vehicle. The charging pad (on the ground) is about 1 m2, while the receiving pad (on the car) is packaged in a small device. In addition to the optional vehicle-mounted pads, the infrastructure also includes an inductive charging station.

The receiver (receiving coil) is placed on the bottom of the vehicle, while several coils used as transmitters are embedded in the road surface. The latter is supplied with electrical energy. Here’s how it works: Coils in the sidewalk pass an electric current to generate a magnetic field. The magnetic field ensures that the coils on the vehicle pick up this magnetic field and convert it back into electrical energy. The energy produced is used to charge the batteries that run the electric motor.

All major technologies are based on resonant coupling between the transmitter and receiver coils, Hussain said. “With this approach, the receive coil can be tuned very well to the transmit frequency to maximize the power delivered through the wireless charging gap,” he said.

Anderson noted that the receiver antenna is mounted on the underside of the vehicle. “The location needs to support a mirrored interface to the transmitter antenna,” he said. “The actual location under the car is less important than ensuring a proper connection to the transmitter antenna. The actual size is determined by the design power transfer rate. With the enclosure, for For electric vehicles, the size of the antenna will range from 24 by 30 inches, ±6 inches of any particular size. The width of the antenna will be between 1.5 and 4 inches, depending on the nature of the associated power electronics.”

Based on the same principle, mobile wireless charging is an alternative to stationary charging. The idea is to install a charging coil just a few centimeters below the asphalt, and with a very high magnetic field strength, the charging coil can charge the car while it’s driving. In order for the system to work properly, the vehicle must be retrofitted with a compatible system.

energy management

Charge management is similar to the current method of charging via wired chargers, battery management systems for electric vehicles. However, Anderson noted that even in this case, charge management may vary slightly depending on the power output conditions of the wireless charging device.

“The key is to understand that the communication between the antennas is based on DC power; since the power from the grid is AC, for the transmitter antenna, it has to be converted to DC,” Anderson said. “The receiver antenna receives power in the form of DC, which can then be converted back to AC to interface with the same electrical infrastructure used by the plug-in interface, or left in DC to interface directly with the DC battery management system. Each time the Efficiency drops slightly when power is converted from AC to DC or from DC to AC. This way most wireless charging devices will work at about 92% (±2%) efficiency. However, this is no less than wired charging devices A lot. Wired charging tends to give 96% ± 2% efficiency.”

Hussain added: “After resonant coupling in the receiving antenna, the power source is AC, which needs to be converted to charge the battery. The next stage after the receiving antenna could be passive (diode) or active (MOSFET) rectification. There are Source rectification has lower losses, but requires more careful control and is generally more expensive relative to silicon devices. However, since lower losses can allow the use of smaller heat sinks or cooling systems, the overall system cost can be Lower. After rectifying the power, there is usually a boost stage that provides isolation and aligns the voltage level with the battery and its state of charge.”

Precautions

Electric vehicles are slowly taking over electrification, but range remains a very difficult issue, as are government regulations. “Wireless charging is easier and almost transparent to the user, but wired charging is more intuitive and people may like the feeling of being plugged into the car,” Hussein said. “Wireless charging will not be faster than AC charging using a car charger, which is usually 11 kW to 20 kW, but fast DC charging will go up to 300 kW to provide very fast charging. It will be a long time before wireless charging becomes part of the infrastructure and gives everyone an option to use, pay and feel Safe way.”

To make wireless battery charging accessible to everyone and anywhere, a network of inductive charging stations needs to be created, with charging pads embedded in the road surface. Inductive charging while driving is the main option for electric vehicles. The only certainty today is that the network of fast-charging stations is expanding, and charging electric vehicles will become easier and easier as electric vehicle charging options develop.

Israeli company Electreon Wireless has been working on mobile wireless charging for some time. In the next few months, the first official tests are planned in Tel Aviv, where charging pads will be installed under the asphalt on a 2-kilometer-long asphalt road, and the electric buses will charge them while driving. Wireless charging of electric trucks on public roads is an important milestone in the commercialization of wireless road technology (Figure 4).

Talking about the solution of wireless charging technology for electric vehicles
Figure 5: WiTricity’s Magnetic Resonance Technology (Source: WiTricity)

Genesis will see wireless charging technology in its eG80 model and a new project codenamed JW. The technology will be implemented through partner WiTricity and will be based on the latest SAE J2954 standard mentioned above. The actual deployment of wireless chargers could begin in the second half of 2021, as current technical requirements separate new buildings from current stalls. Genesis is also developing 7 kW and 11 kW home chargers to enable customers to charge wirelessly in their home garages (Figures 5-6).

Talking about the solution of wireless charging technology for electric vehicles
Figure 6: Genesis car with wireless charging (Source: WiTricity)

WiTricity’s high-efficiency 3.6 to 11 kW EV charging development system provides automakers, Tier 1 suppliers and charging infrastructure suppliers with interoperable wireless charging system designs. The efficient design and architecture of WiTricity has been included in global standardization efforts led by SAE International and IEC/ISO (International); DKE and STILLE projects (Germany); and CATARC (China). WiTricity CEO Alex Gruzen points out on his website that self-driving electric vehicles are the future of personal mobility: “But if there’s no driver, who’s going to charge the car? The answer is clear: no plugs, no wires.”

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