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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. 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.
The transfer of power was the very first attempt using radio waves as a medium. Radio waves were first predicted in 1864 by James C. Maxwell. In 1888, Heinrich Hertz showed evidence of radiowaves using his spark-gap radio transmitter. Nikola 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 foot high tower with a 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.
In the 1960s, much research was put into using microwaves to transmit power. W.C. Brown made what he called a “rectenna”. This device received radio frequencies and converted them into a direct current. Brown succeeded but with low efficiency. Canada successfully flew a fuel-free model airplane in 1987 by transmitting a 2.45 GHz, 10 kW microwave to the model plane.
There were also attempts to transfer power 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.
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.
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.
In California in the 1980s, a bus was produced which was powered by inductive charging, and similar work was being done in France and Germany around this time.
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.
The Wireless Power Consortium (WPC) was established in 2008, and in 2010 they established the Qi standard. 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. The purpose of these organizations is to create standards for inductive charging.
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Applications of inductive charging can be divided into two broad categories: Low power and high power:
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.
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. These technologies provide charging times comparable to wired approaches, and they are rapidly finding their way into mobile devices.
Standards refer to the different set operating systems with which devices are compatible. There are two main standards: Qi and PMA. The two standards operate very similarly, but they use different transmission frequencies and connection protocols. Because of this, devices compatible with one standard are not necessarily compatible with the other standard. However, there are devices compatible with both standards.
Many smart phone manufacturers have started adding this technology into their products. The majority of these phones have adopted the Qi wireless charging standard. Major manufacturers such as Apple and Samsung produce many models of their phones in high volume with Qi capabilities. The popularity of the Qi standard has driven other manufacturers to adopt this as their own standard. Smartphones have become the driver for this technology entering consumers’ homes where many household technologies have been developed to utilize this tech. The current push for Qi technology is in consumer smart phones. As this tech is pushed to the consumers there have been many different ideas of what wireless charging will look like. Samsung and other companies have begun exploring the idea of "surface charging", building an inductive charging station into an entire surface such as a desk or table. Contrarily, Apple and Anker are pushing a dock based charging platform. This includes charging pads and disks that have a much smaller footprint. These solutions are geared for consumers who wish to have smaller chargers that would be located in common areas and could blend in with the current décor of their home. Due to the adoption of the Qi standard of wireless charging, any of these chargers will work with any phone as long as the phone is Qi capable.
Magne Charge inductive charging was employed by several types of electric vehicles around 1998, but was discontinued after the California Air Resources Board selected the SAE J1772-2001, or "Avcon", conductive charging interface for electric vehicles in California in June 2001.
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. 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. Evatran began selling the Plugless L2 Wireless charging system to the public in 2014.
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. 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.
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.
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.
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. 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. UTA, the regional public transportation agency, plans to introduce similar buses in 2018. 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., Later busroutes in Bristol, London and Madrid followed.
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).
Wireless charging is making an impact in the medical sector by means of being able to charge implants and sensors long term that are located beneath the skin. Researchers have been able to print wireless power transmitting antenna on flexible materials that could be placed under the skin of patients. This could mean that under skin devices that could monitor the patient status could have a longer term life and provide long observation or monitoring periods that could lead to better diagnosis from doctors. These devices may also make charging devices like pacemakers easier on the patient rather than having an exposed portion of the device pushing through the skin to allow corded charging this technology would allow a completely implanted device making it safer for the patient. It is unclear if this technology will be approved for use more research is needed on the safety of this devices. While these flexible polymers are safer than ridged sets of diodes they can be more susceptible to tearing during either placement or removal do to the fragile nature of the antenna that is printed on the plastic material. While these medical based application seems very specific the high speed power transfer that is achieved with these flexible antenna is being looked at for larger broader applications.
Work and experimentation is currently underway in designing this technology to be applied to electric vehicles. This will be implemented by using a predefined path or conductors that would transfer power across an air gap and charge the vehicle on a predefined path such as a wireless charging lane. Vehicles that could take advantage of this type of wireless charging lane to extend the range of their on board batteries are already on the road. Some of the issues that are currently preventing these lanes from becoming widespread is the initial cost associated with installing this infrastructure that would benefit only a small percentage of vehicles currently on the road. Another complication is tracking how much power each vehicle was consuming/pulling from the lane. Without a commercial way to monetize this technology, many cities have already turned down plans to include these lanes in their public works spending packages. However this doesn’t mean that cars are unable to utilize large scale wireless charging. The first commercial steps are already being taken with wireless mats that allow electric vehicles to be charged without a corded connection while parked on a charging mat. These large scale projects have come with some issues which include the production of large amounts of heat between the two charging surfaces and may cause a safety issue. Currently companies are designing new heat dispersion methods by which they can combat this excess heat. These companies include most major electric vehicle manufactures, such as Tesla, Toyota, and BMW.
GM Pulls the Plug on Inductive Charging: Letter from General Motors Advanced Technology Vehicles (Letter dated 2002-03-15)
Standardization of Charging Systems
the ARB approved the staff proposal to select the conductive charging system used by Ford, Honda and several other manufacturers
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