What Is Wireless Charging & How Exactly Does It Work?

CONCEPT OF WIRELESS CHARGING:

The steps associated with the process of Wireless Charging are:

Let’s break the complete charging process into two circuits that are the:
Transmitter Circuit
Receiver Circuit

The purpose of the Transmitter circuit is to transform the received voltage into high-frequency alternating current. After the high-frequency current is generated by the transmitter circuit it is fed to the transmitting coil in the very circuit. As the high-frequency alternating current is relinquished through the coil, it induces the magnetic field in the coil and the coil now operates as an electromagnet in accordance with the 2 and Law of Electromagnetic Induction. Now, as the magnetic field in one coil changes, and if the other coil is placed in the sufficiently close distance, the emf will be inducted into the neighbouring coil. The alternating current induces alternating flux in the transmitting coil which induces alternating magnetic flux in the core. As the core extends through secondary so some magnetic flux is linked with secondary also. Now, again the same reversed phenomenon will take place, the induced magnetic field in the Receiver coil will generate the alternating current into the receiver circuit in accordance with the faradays Law of induction. Hence the energy is transmitted from the Transmitter circuit to the Receiving circuit through induction or coupling.Now in the last step, the induced alternating current is converted into required DC Voltage through a series of filters and Rectifier. At last the Stable current is fed into the battery for charging.Consequently, in this way, the wireless charging takes place.

Standard Wireless Power Technologies:
When we talk about wireless charging technology, there are two most common prevailing technologies in the market. They are:Wireless Power Consortium (WPC) and the Power Matters Alliance (PMA). The Wireless Technology isin the market from a decade, in order to make this technology for the use of market consumers hence Wireless Power Consortium (WPC) was formed in 2008 to standardize the development of wireless charging solutions. After that PMA was introduced in 2012 to serve the same purpose.
Both PMA and WPC are similar techniques and works on the same principle of Magnetic Induction but differs in the frequency of Operation and different connection protocols.

From: https://www.idt.com/products/power-management/wireless-power/introduction-to-wireless-battery-charging

From: http://techlife.samsung.com/6-times-wireless-charging-comes-handy-1557.html

OVERVIEW:
Talking about WPC Charging Standard, it is an open membership organization that maintains the charging standards; one of them is Qi Standard. The Qi standard is the most common standard contributing to more than 90% of the market standard and is available on many mobile devices and market leaders like Samsung, HTC, Nokia and Apple Phones.
The devices which charged through Qi standard, need a physical connection with the charging source. The Qi Technology currently supports wireless power transfer of up to 5W over distances up to 5 mm, but it is developing to deliver up to 15 W, and thereafter to 120 W over much larger distances.

In Qi Standard, there is a requirement of a physical connection between the device and the charging source. The Source also called the base station provides the inductive power to the mobile devices. The Base station consists of a Transmitter which generates alternating emf and the mobile device contains a receiver circuit having receiver coil embedded in it. The next step is the Alternating EMF induces the current in the receiver coil through mutual induction. Also, Qi technique works by using resonant inductive between the station and the device.

The operating frequency is 100–200khz. On Similar principles, the PMA Technology works on the same inductive principle but operates on a different frequency range (usually double than that of Qi Standard). In recent days, the PMA and A4WP signed an agreement to create a merged standard (now the Air-fuel Alliance). This technology is based on a different principle called
magnetic resonance(‘MR’). In the early stages, the standard allowed power delivery is of 3.5 W and 6.5 W, but recently this has been increased to 50 W. As both the technologies work on magnetic coupling, but A4WP consists of more loosely coupled, yet more tightly tuned receiver and transmitter coils, with a very high Q (quality factor). As such, Air-fuel offers more flexibility with respect to physical placement of transmitter to the receiver.

Inductive vs. Resonant Charging Technologies:
The above discussed wireless charging standards work on Inductive and Resonant Technologies. The Inductive technology is the type of compliance primarily used by Qi Standard on Charging. This technology uses closely coupled coils and transmit power only over very short distances using low frequency resonant tanks. The Distance to which the transmission of power takes place is less than 10mm. In 2009, initially, when Qi standard makes its appearance in the consumer market. The power requirement at that time is considered very low (about 5 W). As the time progressed, the power delivering capability through Qi standard increased to 15W capability (“Medium Power”) in 2012. Experimental Results and Testing confirmed that Soon Qi technology is aiming for 100W Power Transmission.

The drawback of transmitting power through very short distances is overcome by the other wireless power technology, resonant, that is considered a loosely coupled solution. By this technology, we can transmit power over large distances (many folds larger than the Inductive coupling).The Frequency on which the Resonant Technology works is higher than the Inductive one. Also, another advantage of Resonant Technology is the ability to charge multiple devices at 22W. The magnetic resonance coupling typically hits in the megahertz frequency spectrum, the quality factors are usually high. With the increase of charging range, the high-quality factor helps to alleviate the sharp decrease in coupling efficiency and thus charging efficiency.

From: http://wirelesspowerrenaissance.blogspot.in/2014/05/ieee-p21001-a4wp-pma-wpc.html

 From: www.mediatek.com