The rise of electric vehicles is transforming the future of transportation, and with their increasing affordability, they are becoming a popular choice for consumers. In fact, it is anticipated that electric cars will outnumber their gasoline counterparts on the roads by 2030. Currently, most electric vehicles can travel between 300 to 400 kilometers on a single charge, which is more than enough for daily driving needs. Moreover, the battery pack of an electric car is expected to have a lifespan of at least five to eight years before needing any repairs or replacement of cells.
The increasing number of electric cars on the road has led to a significant rise in the demand for charging stations. Despite the US having 56,000 charging stations with a total of 148,000 charging ports, it is still not enough to meet the growing demand for EVs. In countries such as India, the need for EV charging stations is expected to reach 700,000 by 2030. Although fast-charging electric cars is a major challenge, setting up nationwide charging facilities is another obstacle that needs to be addressed.
As the demand for an efficient and comprehensive EV charging infrastructure increases, automotive companies are exploring new avenues to charge electric vehicles. Wireless EV charging stations (WEVCS) are one promising solution for charging multiple EVs simultaneously. These stations function similarly to wireless chargers used for mobile phones and can be installed in parking lots to enable automatic charging of EVs while they are parked. Another alternative is dynamic wireless charging, which allows EVs to charge while in motion. Although dynamic charging offers an extended EV range, there are concerns about potential environmental and health hazards.
Static wireless charging
The most practical and secure form of wireless charging technology is static wireless charging. This technique allows electric vehicles to be charged wirelessly while they are stationary at a charging station. The installation of such a system is effortless and can be done in parking lots and garages. In static wireless charging, the transmitter is placed underground, and the electric vehicle has an onboard receiver at the bottom. When the car is parked in a designated spot, the transmitter and receiver align automatically, and the charging process begins without any need for plugging in cables. The rate of charging depends on the AC voltage level, and the car can be charged efficiently while it remains parked.
Dynamic wireless charging
Dynamic charging is a concept for EV charging infrastructure that involves installing stationary power transmitters on roads and highways. Electric vehicles charge while in motion as they come into the vicinity of these transmitters. This charging technology promises a longer range for EVs on the go. However, implementing dynamic charging would come at a significant cost, as it requires constructing the equivalent of EV charging setups across entire roads and highways. There are also concerns about the effectiveness of charging moving vehicles since wireless charging requires perfect alignment of the transmitter and receiver. In addition, such a setup poses potential safety risks, environmental effects, and health hazards.
How wireless charging works
The concept of wireless charging has been around since Nicola Tesla developed the Tesla Coil, which demonstrated the basic principles of wireless charging. Wireless charging operates on the same principle as a transformer, where the secondary coil is excited by the magnetic field generated by the current flowing in the primary coil. In wireless charging, a transmitter and a charging device with a receiver are used. When alternating current flows through the transmitter, an alternating magnetic field is generated, which transfers current to the receiver, enabling charging. While there are several different methods of wireless charging, there are four recognized methods as follows:
- Capacitive Wireless Charging System (CWCS)
- Permanent Magnetic Gear Wireless Charging System (PMWC)
- Inductive Wireless Charging System (IWC)
- Resonant Inductive Wireless Charging System (RIWC)
Capacitive Wireless Charging System (CWCS)
This type of wireless charging relies on electrostatic induction, similar to that seen in capacitors. A receiver plate is located at the bottom of the electric car, while a transmitter plate is situated on the ground at the charging station. The air gap between the plates serves as a dielectric medium. The electric car is charged by a displacement current generated in the receiver plate due to changes in the electric field created by the transmitter plate.
At the charging station, AC current is first supplied to a power factor correction circuit that maintains voltage levels and minimizes transmission losses. The voltage is then passed through an H-bridge, which generates a high-frequency AC voltage in the range of 100 to 600 KHz. This high-frequency AC voltage produces an oscillating electric field, which generates a displacement current in the receiver plate. The amount of current received at the receiver plate depends on various factors, such as the alignment of the transmitter and receiver plates, the air gap between the two plates, the applied AC voltage, the material used in the construction of the plates, and the frequency of the AC voltage.
At the receiver side, the displacement current is used to charge the battery pack of the electric car with the aid of a rectifier and filter circuit. This technology ensures efficient and safe wireless charging without the need for cables or direct contact.
Permanent Magnetic Gear Wireless Charging System (PMWC)
This wireless charging method is based on the same principle as an electric motor, with both the transmitter and receiver containing an armature winding and synchronized permanent magnets. When AC voltage is applied to the transmitter winding, mechanical torque is generated due to the permanent magnets. Changes in the permanent magnetic field of the transmitter causes synchronized mechanical torque to be induced in the receiver’s permanent magnet, generating AC current in the receiver winding. The receiver effectively becomes a power generator as the mechanical torque in its permanent magnet is converted to alternating current in its winding. The coupling of rotating permanent magnets is called magnetic gear. At the receiver side, the AC current generated by the magnetic gear is rectified and filtered to charge the battery pack of the electric car.
Wireless charging based on the principle of an electric motor utilizes armature windings with synchronized permanent magnets in both transmitter and receiver. When an AC voltage is applied to the transmitter winding, mechanical torque is generated due to the permanent magnets. This change in the magnetic field produces synchronized mechanical torque in the receiver’s permanent magnet, which generates AC current in the receiver winding. This process turns the receiver into a power generator, and the coupling of rotating permanent magnets is referred to as a magnetic gear. The AC current generated by the magnetic gear is rectified and filtered at the receiver end to charge the battery pack of the electric car. Regenerate response
This method of wireless charging has several disadvantages that need to be considered. Firstly, due to the use of permanent magnets, the charging setup can be more expensive than other methods. Secondly, permanent magnets are vulnerable to damage under mechanical stress, which could lead to high maintenance costs over time.
Inductive wireless charging is a method based on the working principle of a transformer. In this setup, both the transmitter and receiver have coils. The transmitter coil is installed on the ground, while the receiver coil is at the bottom of the electric car. An AC voltage with a frequency range of 19-50 KHz is applied to the transmitter coil. This creates a change in the magnetic field at the receiver coil, inducing AC current. The AC current is then rectified and filtered to charge the electric car’s battery pack via its battery management system. This method of wireless charging is cost-effective and straightforward to implement, as it works similarly to electricity transfer between primary and secondary windings in a transformer. As transformers are one of the cheapest and easiest electronic components to construct, this method of wireless charging is the most economical and simplest to set up. The alignment of the coils is crucial for wireless charging, and the rate of charging depends on the distance between the transmitter and receiver coil, mutual inductance, and frequency of the AC supply.
Inductive Wireless Charging System (IWC) is a type of wireless charging technology that is based on the working principle of a transformer. The IWC consists of a transmitter coil, which is installed at the ground, and a receiver coil, which is placed at the bottom of the electric car.
To charge the electric car, an AC voltage of frequency in the range of 19~50 KHz is passed through the transmitter coil. This causes a change in the magnetic field at the receiver coil, producing AC current. The AC current inducted in the receiver coil is then rectified and filtered to charge the battery pack of the electric car using its battery management system.
One of the main advantages of IWC is its cost-effectiveness. As the charging setup works just like the transfer of electricity between the primary and secondary winding of a transformer, it is one of the most economical and easiest to implement wireless charging methods. The coils, however, need to be in alignment for wireless charging to work effectively. The rate of charging in an inductive wireless charging system depends on the distance between the transmitter and receiver coil, the mutual inductance between them, and the frequency of the applied AC supply.
Resonant Inductive Wireless Charging System (RIWC)
Inductive wireless charging is a method of wirelessly charging electric vehicles. The charging process is based on the principle of electromagnetic induction used in transformers. In this setup, a transmitter coil is installed on the ground, and a receiver coil is placed at the bottom of the electric car. An AC voltage with a frequency in the range of 19~50 KHz is supplied to the transmitter coil.
This AC voltage causes a change in the magnetic field, which in turn produces an AC current in the receiver coil. The AC current produced in the receiver coil is rectified and filtered by the car’s battery management system to charge the battery pack of the electric car.
This charging system is cost-effective compared to other wireless charging methods as it uses a simple setup of coils that work similarly to a transformer. As transformers are one of the most affordable electronic components and easiest to construct, this method of wireless charging is the most economical and simplest to implement.
However, the coils need to be in alignment for wireless charging, and the rate of charging depends on the distance between the transmitter and receiver coil, the mutual inductance between them, and the frequency of the applied AC supply.
Challenges in EV wireless charging
Wireless charging of electric vehicles using permanent magnet gear works on the principle of an electric motor. The charging system consists of a transmitter and a receiver. Both the transmitter and receiver have an armature winding with synchronized permanent magnets placed as the core within the windings.
When AC voltage is applied to the transmitter winding, mechanical torque is generated due to the permanent magnets. Changes in the permanent magnetic field of the transmitter cause synchronized mechanical torque to be induced in the receiver’s permanent magnet, producing AC current in the receiver winding. The receiver is converted into a power generator as the mechanical torque in the receiver’s permanent magnet is converted to alternating current in its winding. The coupling of rotating permanent magnets is called magnetic gear.
The AC current from the magnetic gear is rectified and filtered at the receiver side to charge the battery pack of the electric car. However, this method of wireless charging has several disadvantages. The use of permanent magnets makes the charging setup costly, and they are prone to breaking under mechanical stress. This could lead to high maintenance costs.
WEVCS standards
Several global organizations, including the Society of Automotive Engineers (SAE), the International Electrotechnical Commission (IEC), and the Institute of Electrical and Electronics Engineers (IEEE), are collaborating to establish a worldwide standard for wireless EV charging. While plug-in charging has an efficiency range of 94 to 94.5 percent, the latest standards developed by the SAE for wireless charging have shown an efficiency range of 90 to 92 percent, significantly reducing the efficiency gap between wired and wireless charging and making it a more viable option for EV owners.
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