Wireless Charging is of Great and Meaningful Significance in the Near Future

This technology will create a major change in the process of wireless power transfer. This will also have a sustainable impact on the performance of the vehicles. The technique of wireless power transfer requires no physical contact between the charging device and the device to be charged. These technology's mostly use resonant magnetic induction to transfer energy (electricity) without any wired connection from a ground based device to the power receiving device which would be installed in the base of the electric vehicles. This wireless power transfer technique overcomes the inconvenience and hazard caused by a traditional conductive charging method, as devices with cables can suffer mechanical compatibility problems and higher failure rate.

A device or battery bank that has to be charged will need to be placed above a transmitter. Wireless power transfer used for charging would be significantly increased in the future as it allows consumers not to carry wired devices that can easily wear out in a short period of time and are also uncomfortable to carry in the true sense. Significant breakthroughs are achieved to integrate this technology whether it be a cell phone or a vehicle. Immense growth has been found in the global wireless vehicle market. By 2025 it will become a dominant technology.

Framework of Wireless Charging

Framework of Wireless Charging

The AC/DC current supplied by a power source is changed into high frequency AC current by the transmitter section which has a copper coil (transmitter coil), by which a magnetic field is generated. The Magnetic field will induce an AC current in the receiver coil when the receiver coil is in the proximity of the transmitter. This induced AC current is converted back into DC and used to charge the batteries.

Capacitors that have been used for electric vehicle charging stations and on board units are DC link and power film capacitors. Useful characteristic's offered by film capacitors are low equivalent series resistance (ESR), low equivalent series inductance (ESL), self-healing as well as excellent dielectric capacity to operate at high voltage, high current and high temperatures.

Good efficiency of the transmitter and receiver is obtained by using DC link capacitors. DC link capacitor is used after rectification and power film capacitor is used for resonance across the coil.

Classification of Wireless Power Transfer Technologies

Time-varying electromagnetic field

  • 1) Near-field
  • 2) Far-field

Basically the near-field technology is non-radiative and it can transfer energy over a short distance. An extended operating range as well as sufficiently high efficiency is procured by allowing adequate magnetic resonance. Whereas in far-field technology energy is transferred from two wavelengths to infinity through the propagation of electromagnetic waves.

Electric field power transfer

An alternating electric field is used to transfer energy in capacitive wireless power transfer technology. It has a smaller EMI foot print (electromagnetic interference) than traditional electromagnetic-field-based technologies, because the electric flux tends to travel within the conductive plates, while the magnetic flux tends to spread in all directions from the coils to make a closed flux loop.

Different Forms of Near-Field Coupling Techniques

  1. Inductive Coupling:- In the inductive charging method electromagnetic waves are used to transfer energy for wireless charging. In inductive power transfer inductive coupling can only achieve high efficiency when the coils are very close together. Basically this form of charging is used for small devices like smart-phones, etc.
  2. Resonant inductive Coupling:- Large devices, batteries (e.g. cars, laptops), medical equipment, etc. makes use of resonance charging. In the most modern inductive system resonant inductive coupling is used, in which the efficiency is increased by using resonant circuits. In resonance charging transmitter coil and receiver coil are tuned to the same electromagnetic frequency. The device that has to be charged needs to be placed over a transmitter. The transmitter and receiver coil need not to be placed very close to each other.
  3. Capacitive Wireless Power Transfer (CWPT):- There has been a potential advantage of CWPT system over the inductive system, because the nature of electric fields is relatively directed, which in terms reduces the need for electromagnetic field shielding. It is one of the promising technologies to achieve efficient wireless power transfer.

CWPT system makes use of an electric field instead of magnetic field for energy transmission through the isolation barrier which allows it to reduce EMI. The transmitter side consists of the transmitter unit along with a pair of transmitting conductors whereas receiver side also consists of a receiver unit and a receiver conductors. In addition there is no complex coil configuration which makes the system less expensive and possibly more compact.

CWPT system is operated at a high frequency, and it mainly allows three advantages: negligible eddy current loss, relatively low cost, low weight, and allows considerable amount of misalignment without adversely affecting performance. In recent years, the power level and efficiency have been significantly improved, which is suitable for charging of a electric vehicle.

Capacitive WPT system architecture

CWPT Architecture

Figure 2. Capacitive WPT System Architecture.

CWPT makes use of parallel plates and electric field coupling between the transmitter and receiver modules. As shown in figure 2 this topology consists of an oscillator in the primary side and flat conductive plates as a transmitter. The secondary side has conductive plate as a receiver of the electric field, forming a coupling capacitance followed by a rectifier.

Wireless charging technology will become more widespread by 2025. On our journey to a more wireless world, we are going to see a change in not only the ways that we interact with our devices, but also in our entire environment.

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