Inductive charging

Inductive charging (also known as wireless charging or cordless charging) uses an electromagnetic field to transfer energy between two objects through electromagnetic induction. This is usually done with a charging station. Energy is sent through an inductive coupling to an electrical device, which can then use that energy to charge batteries or run the device.

Induction chargers use an induction coil to create an alternating electromagnetic field from within a charging base, and a second induction coil in the portable device takes power from the electromagnetic field and converts it back into electric current to charge the battery. The two induction coils in proximity combine to form an electrical transformer.^[1]^[2] Greater distances between sender and receiver coils can be achieved when the inductive charging system uses resonant inductive coupling.

Recent improvements to this resonant system include using a movable transmission coil (i.e. mounted on an elevating platform or arm) and the use of other materials for the receiver coil made of silver plated copper or sometimes aluminium to minimize weight and decrease resistance due to the skin effect.

History

The transfer of power was first attempted using radiowaves as a medium. Radiowaves were first predicted in 1864 by James C. Maxwell. In 1888, Heinrich Hertz showed evidence of radiowaves using his spark-gap radio transmitter. Nicola Tesla believed that wireless power transfer was possible and probable. He built what was called the “Tesla Tower” which was a giant coil connected to a 200 feet high tower with ball 3 feet in diameter. Tesla pumped 300kw of power into the device; the coil resonated at 150 kHz. The experiment failed due to the fact that the power diffused in all directions.^[3]

In the 1960’s, much research was put into using microwaves to transmit power. W.C. Brown made what he called a “rectenna”. This device received radiofrequencies and converted them into a direct current. Brown succeeded but with low efficency. Canada successfully flew a fuel-free airplane in 1987 by transmitting a 2.45 GHz, 10 kW microwave to the model plane.^[4]

Power was also attempted to be transferred through induction. This was first used when, in 1894, M. Hutin and M. Le-Blanc proposed an apparatus and method to power an electric vehicle. However, combustion engines proved more popular and this technology was forgotten for a time.^[5]

In 1972, Professor Don Otto of the University of Auckland proposed a vehicle powered by induction using transmitters in the road and a receiver on the vehicle.^[6]

The first application of inductive charging used in the United States was performed by J.G. Bolger, F.A. Kirsten, and S. Ng in 1978. They made an electric vehicle powered with a system at 180 Hz with 20 kW.^[7]

In California in the 1980’s, a bus was produced which was powered by inductive charging, and similar work was being done in France and Germany around this time.^[8]

In 2006, MIT began using resonant coupling. They were able to transmit a large amount of power without radiation over a few meters. This proved to be better for commercial need, and it was a major step for inductive charging.^[9]

The Wireless Power Consortium (WPC) was established in 2008, and in 2010 they established the standard Qi. In 2012, the Alliance for Wireless Power (A4WP) and the Power Matter Alliance (PMA) were founded. Japan established Broadband Wireless Forum (BWF) in 2009, and they established the Wireless Power Consortium for Practical Applications (WiPoT) in 2013. The Energy Harvesting Consortium (EHC) was also founded in Japan in 2010. Korea established the Korean Wireless Power Forum (KWPF) in 2011.^[10] The purpose of these organizations is to create standards for inductive charging.

Application areas

Applications of inductive charging can be divided into to two broad categories: Low power and high power:

Low power applications are generally supportive of small consumer electronic devices such as cell phones, handheld devices, some computers, and similar devices which normally charge at power levels below 100 watts.
High power inductive charging generally refers to inductive charging of batteries at power levels above 1 kilowatt. The most prominent application area for high power inductive charging is in support of electric vehicles, where inductive charging provides an automated and cordless alternative to plug-in charging. Power levels of these devices can range from approximately 1 kilowatt to 300 kilowatts or higher. All high power inductive charging systems use resonated primary and secondary coils.

Advantages

Protected connections – No corrosion when the electronics are all enclosed, away from water or oxygen in the atmosphere. Less risk of electrical faults such as short circuit due to insulation failure, especially where connections are made or broken frequently.^[11]
Low infection risk – For embedded medical devices, transmission of power via a magnetic field passing through the skin avoids the infection risks associated with wires penetrating the skin.^[12]
Durability – Without the need to constantly plug and unplug the device, there is significantly less wear and tear on the socket of the device and the attaching cable.^[13]
Increased convenience and aesthetic quality – No need for cables.
Automated high power inductive charging of electric vehicles allows for more frequent charging events and consequential driving range extension.
Inductive charging systems can be operated automatically without dependence on people to plug and unplug. This results in higher reliability.
Autonomous driving technology, when applied to electric vehicles, depends on autonomous electric charging—automatic operation of inductive charging solves this problem.
Inductive charging of electric vehicles at high power levels enables charging of electric vehicles while in motion (also known as dynamic charging).

Disadvantages

The following disadvantages have been noted for low power (i.e., less than 100 watts) inductive charging devices. These disadvantages may not be applicable to high power (i.e. greater than 5 kilowatts) electric vehicle inductive charging systems.

Slower charging – Due to the lower efficiency, devices take longer to charge when supplied power is the same amount.
More expensive – Inductive charging also requires drive electronics and coils in both device and charger, increasing the complexity and cost of manufacturing.^[1]^[2]
Inconvenience - When a mobile device is connected to a cable, it can be moved around (albeit in a limited range) and operated while charging. In most implementations of inductive charging, the mobile device must be left on a pad to charge, and thus can't be moved around or easily operated while charging. With some standards, charging can be maintained at a distance, but only with nothing present in between the transmitter and receiver.^[14]
Compatible standards – Not all devices are compatible with different inductive chargers. However, some devices have started to support multiple standards.^[15]
Inefficiency – Inductive charging is not as efficient as direct charging which causes the phone to get hot. Continued exposure to heat can result in battery damage.^[16]
Cords – One major advantage is that devices can be charged without cords, but this is not entirely true. There is no direct connection to the device being charge; however, cords are required to provide power to the transmitter.^[17]

Newer approaches reduce transfer losses through the use of ultra thin coils, higher frequencies, and optimized drive electronics. This results in more efficient and compact chargers and receivers, facilitating their integration into mobile devices or batteries with minimal changes required.^[18]^[19] These technologies provide charging times comparable to wired approaches, and they are rapidly finding their way into mobile devices.

For example, the Magne Charge vehicle recharger system employs high-frequency induction to deliver high power at an efficiency of 86% (6.6 kW power delivery from a 7.68 kW power draw).^[20]

Standards

Standards refer to the different set operating systems with which devices are compatible. There are two main standards: Qi and PMA.^[21] The two standards operate very similarly, but they use different transmission frequencies and connection protocols.^[22] Because of this, devices compatible with one standard are not necessarily compatible with the other standard. However, there are devices compatible with both standards.

Magne Charge, a largely obsolete inductive charging system, also known as J1773, used to charge battery electric vehicles (BEV) formerly made by General Motors.
Qi, an interface standard developed by the Wireless Power Consortium for inductive electrical power transfer. At the time of July 2017, it is the most famous standard in the world, more than 200 million devices supporting this interface.
AirFuel Alliance:
- In January 2012, the IEEE announced the initiation of the Power Matters Alliance (PMA) under the IEEE Standards Association (IEEE-SA) Industry Connections. The alliance is formed to publish set of standards for inductive power that are safe and energy efficient, and have smart power management. The PMA will also focus on the creation of an inductive power ecosystem^[23]
- Rezence was an interface standard developed by the Alliance for Wireless Power (A4WP).
- A4WP and PMA merged into the AirFuel Alliance in 2015.

Examples

Portable electronics and devices

Oral-B rechargeable toothbrushes by the Braun company have used inductive charging since the early 1990s.
At the Consumer Electronics Show (CES) in January 2007, Visteon unveiled its inductive charging system for in vehicle use that could charge only specially made cell phones to MP3 players with compatible receivers.^[24]
April 28, 2009: An Energizer inductive charging station for the Wii remote was reported on IGN.^[25]

At CES in January 2009, Palm, Inc. announced its new Pre smartphone would be available with an optional inductive charger accessory, the "Touchstone". The charger came with a required special backplate that became standard on the subsequent Pre Plus model announced at CES 2010. This was also featured on later Pixi, Pixi Plus, and Veer 4G smartphones. Upon launch in 2011, the ill-fated HP Touchpad tablet (after HP's acquisition of Palm Inc.) had a built in touchstone coil that doubled as an antenna for its NFC-like Touch to Share feature .^[18]^[26]^[27]
Nokia announced on September 5, 2012, the Lumia 920 and Lumia 820, which supports respectively integrate inductive charging and inductive charging with an accessory back.
March 15, 2013 Samsung launched the Galaxy S4, which supports inductive charging with an accessory back.
July 26, 2013 Google and ASUS launched the Nexus 7 2013 Edition with integrated inductive charging.
September 9, 2014 Apple announced Apple Watch (released on April 24, 2015), which uses wireless inductive charging.
September 12, 2017 Apple announced the AirPower wireless charging mat. It is capable of charging an iPhone, an Apple Watch and AirPods simultaneously.

Qi devices

Nokia launched two smartphones (the Lumia 820 and Lumia 920) on 5 September 2012, which feature Qi inductive charging.^[28]

Google and LG launched the Nexus 4 in October 2012 which supports inductive charging using the Qi standard.
Motorola Mobility launched its Droid 3 and Droid 4, both optionally support the Qi standard.
On November 21, 2012 HTC launched the Droid DNA, which also supports the Qi standard.
October 31, 2013 Google and LG launched the Nexus 5, which supports inductive charging with Qi.
April 14, 2014 Samsung launched the Galaxy S5 that supports Qi wireless charging with either a wireless charging back or receiver.
November 20, 2015 Microsoft launched the Lumia 950 XL and Lumia 950 which support charging with the Qi standard.
February 22, 2016 Samsung announced its new flagship Galaxy S7 and S7 Edge which use an interface that is almost the same as Qi.
September 12, 2017 Apple announced that the iPhone 8 and iPhone X would feature wireless Qi standard charging.


Furniture

Ikea has a series of wireless charging furniture that support the Qi standard.

Dual standard

March 3, 2015 Samsung announced its new flagship Galaxy S6 and S6 Edge with wireless inductive charging through both Qi and PMA compatible chargers.
November 6, 2015 BlackBerry released its new flagship BlackBerry Priv, the first BlackBerry phone to support wireless inductive charging through both Qi and PMA compatible chargers.

Research and other

Transcutaneous Energy Transfer (TET) systems in artificial hearts and other surgically implanted devices.
In 2006, researchers at the Massachusetts Institute of Technology reported that they had discovered an efficient way to transfer power between coils separated by a few meters. The team, led by Marin Soljačić, theorized that they could extend the distance between the coils by adding resonance to the equation. The MIT inductive power project, called WiTricity, uses a curved coil and capacitive plates.^[29]^[30]

In 2012 a Russian private museum Grand Maket Rossiya opened featuring inductive charging on its model car exhibits.

Transportation

Electric vehicles

Hughes Electronics developed the Magne Charge interface for General Motors. The General Motors EV1 electric car was charged by inserting an inductive charging paddle into a receptacle on the vehicle. General Motors and Toyota agreed on this interface and it was also used in the Chevrolet S-10 EV and Toyota RAV4 EV vehicles.
September 2015 AUDI Wireless Charging(AWC) presented a 3.6 kW inductive charger ^[31] during the 66th International Motor Show (IAA) 2015.
September 17, 2015 Bombardier-Transportation PRIMOVE presented a 3.6 kW Charger for cars,^[32] which was developed at Site in Mannheim Germany.^[33]
Transport for London has introduced inductive charging in a trial for double-decker buses in London.^[34]

Magne Charge inductive charging was employed by several types of electric vehicles around 1998, but was discontinued^[35] after the California Air Resources Board selected the SAE J1772-2001, or "Avcon", conductive charging interface^[36] for electric vehicles in California in June 2001.^[37]

In 1997 Conductix Wampler started with wireless charging in Germany, In 2002 20 buses started in operation In Turin with 60 kW charging. In 2013 the IPT technology was bought by Proov. In 2008 the technology was already used in the house of the future in Berlin with Mercedes A Class. Later Evatran also began development of Plugless Power, an inductive charging system it claims is the world’s first hands-free, plugless, proximity charging system for Electric Vehicles.^[38] With the participation of the local municipality and several businesses, field trials were begun in March 2010. The first system was sold to Google in 2011 for employee use at the Mountain View campus.^[39] Evatran began selling the Plugless L2 Wireless charging system to the public in 2014.^[40]

Research and other

Stationary

In one inductive charging system, one winding is attached to the underside of the car, and the other stays on the floor of the garage.^[41] The major advantage of the inductive approach for vehicle charging is that there is no possibility of electric shock, as there are no exposed conductors, although interlocks, special connectors and RCDs (ground fault interruptors, or GFIs) can make conductive coupling nearly as safe. An inductive charging proponent from Toyota contended in 1998 that overall cost differences were minimal, while a conductive charging proponent from Ford contended that conductive charging was more cost efficient.^[42]

From 2010 onwards car makers signalled interest in wireless charging as another piece of the digital cockpit. A group was launched in May 2010 by the Consumer Electronics Association to set a baseline for interoperability for chargers. In one sign of the road ahead a General Motors executive is chairing the standards effort group. Toyota and Ford managers said they also are interested in the technology and the standards effort.^[43]

Daimler’s Head of Future Mobility, Professor Herbert Kohler, however have expressed caution and said the inductive charging for EVs is at least 15 years away (from 2011) and the safety aspects of inductive charging for EVs have yet to be looked into in greater detail. For example, what would happen if someone with a pacemaker is inside the vehicle? Another downside is that the technology requires a precise alignment between the inductive pick up and the charging facility.^[44]

In November 2011, the Mayor of London, Boris Johnson, and Qualcomm announced a trial of 13 wireless charging points and 50 EVs in the Shoreditch area of London's Tech City, due to be rolled out in early 2012.^[45]^[46] In October 2014, the University of Utah in Salt Lake City, Utah added an electric bus to its mass transit fleet that uses an induction plate at the end of its route to recharge.^[47] UTA, the regional public transportation agency, plans to introduce similar buses in 2018.^[48] In November 2012 wireless charging was introduced with 3 buses in Utrecht. January 2015, eight electric buses were introduced to Milton Keynes, England, which uses inductive charging in the road with proov/ipt technology at either end of the journey to prolong overnight charges.,^[49] Later busroutes in Bristol, London and Madrid followed.

Dynamic

Researchers at the Korea Advanced Institute of Science and Technology (KAIST) have developed an electric transport system (called Online Electric Vehicle, OLEV) where the vehicles draw power from cables underneath the surface of the road via non-contact magnetic charging (where a power source is placed underneath the road surface and power is wirelessly picked up on the vehicle itself). As a possible solution to traffic congestion and to improve overall efficiency by minimizing air resistance and so reduce energy consumption, the test vehicles followed the power track in a convoy formation. In July 2009 the researchers successfully supplied up to 60% power to a bus over a gap of 12 centimetres (4.7 in).^[50]

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