Wireless energy transfer
In the wireless energy transfer ( contactless power transmission, wireless power transmission or contactless power transfer ) energy is transferred from one object to another. This may involve various forms of energy, for example, kinetic or electrical energy. Generally including an electric structure meant the electrical power required for operation is not supplied via cable and electrical contacts, but. Through the use of electromagnetic fields, or other physical principles operative The benefits include increased mobility and no electrical contact problems. Moreover, by a waterproof construction of the components is possible.
The most common English words are wireless power ( power transmission, power transfer), contactless power ( power transmission, power transfer), wireless energy ( energy transmission, energy transfer) or contactless energy ( energy transmission, energy transfer). The most widely used is the method of inductive energy transfer. Frequently wireless power transmission is used synonymously for inductive energy transfer.
- 2.1 Inductive energy transfer 2.1.1 principle
- 2.1.2 Frequency Range
- 2.1.3 resonance operation
- 2.1.4 efficiency
- 2.2.1 principle
- 2.2.2 Frequency Range
- 2.2.3 resonance operation
- 2.2.4 efficiency
- 2.3.1 principle
- 2.3.2 Frequency Range
- 2.3.3 properties
- 2.4.1 principle
- 2.4.2 properties
- 2.4.3 Availability
- 4.1 Mobile Devices 4.1.1 Qi
- 4.1.2 Power Mats
- 4.1.3 Rezence
- 4.1.4 Convergence of Powermat technology and Rezence
Application
For many applications, a wireless power transmission is not yet technically feasible. Above all applications with the following boundary conditions are suitable:
- Small distance between the transmitter and receiver power
- Low energy consumption
- Long loading time with a short operating time
Considering the proliferation of wireless energy transfer based on the active principles used, one finds that most applications are based on the principle of inductive energy transfer. Here are some for longer commercially available products. The other principles are less common and the applications are mostly in the advanced stage of development or early product stage. The following are some applications are listed:
Inductive power transmission
Consumer electronics
- Mobile devices: mobile phones, music players, cameras, batteries
- Laptop computer
- TVs
- Heat Shoes
- Computer Mouse
- Hygiene tools: toothbrush, shaver, hand massager
- Decorative lighting: mood lamps
Industry
- Autonomous transportation vehicles
- Inductive heating
- Transport of liquid metals
- Tool stations
- Power transfer to rotating and moving parts
- Sensor systems
Traffic
- Electric bicycle
- Electric car
- Electric buses
Medicine
- Implants ( cardiac pump, cochlea, retina, heart pacemakers)
- Autonomous endoscope
- Sensors
Capacitive energy transfer
- Recharge mobile devices
Electromagnetic energy transfer
- RFID devices
- Passive radio receiver ( detector receiver )
- Decorative lighting, such as Christmas tree lighting
Active principles
There are several active principles, which can be used for contactless power transmission. The most important are:
- Inductive power transmission
- Capacitive energy transfer
- Electromagnetic energy transfer
- Contactless energy transfer by means of LASER
- Contactless energy transfer using ultrasound
Inductive power transmission
Inductive power transmission is the most common method for contactless power transfer. Frequently, the term " non-contact power transmission " are used synonymously for " inductive power transfer ".
Principle
For the inductive energy transfer (transmitter, generator ) will generates an alternating magnetic field in the transmitter. This is done by means of a coil (transmitter coil), which is flowed through by an alternating current. The receiver ( engl. receiver ) also contains a coil. It is penetrated by a part of the alternating magnetic field. Thereby a voltage is induced in the receiver coil. When an electrical load is connected to the coil, it is due to the induced voltage to the current flow through the load and power is transmitted. The principle is that of a transformer having a weak coupling of the coils.
Frequency range
The frequency range used is from some 10 kHz up to the MHz range as well. In this frequency range, the dispersion does not matter for use as an electromagnetic wave. The receiver is located in the magnetic near field of the transmitter and the calculations are done assuming a quasi-static magnetic field.
Resonance operation
Conventionally used in the receiver and in the transmitter resonant capacitors which form resonance circuits with the coil (or oscillator circuits ). Create different resonances that can be used differently depending on the vote to
- To maximize the transmitted power,
- To optimize the efficiency of power transmission,
- Adjusted by varying the frequency of the transmitted power,
- Adjust the required load characteristics of the transmitted power,
- To compensate for variations in the magnetic coupling,
- Match the impedance of the transmitter coil to the requirements of the AC generator,
- To compensate for the magnetizing current of the transmitter coil in order to reduce losses in the generator,
- To achieve a filtering effect to suppress higher frequency components of the generator.
Often, close the different requirements from each other, so that is almost always a compromise on the resonance characteristics necessary.
The term " resonant energy transfer " (English resonant power transmission ) describes systems that use the resonances of the first-mentioned reason. This is especially useful for larger distances, such as over 120 years ago Nikola Tesla has already shown. The active principle of " resonance energy transfer " differs in no way from that of the inductive energy transfer, as described here. Only the wording differs from the generally used.
Efficiency
Losses occur exclusively in the coils as line losses and optionally in the shielding material as eddy current losses and hysteresis losses in normal operation. Further losses occur, as in any power electronic system, the generator of the transmitter and the receiver in the rectifier. Radiation losses of the magnetic field are negligible. In case of error losses can be induced in metallic or soft magnetic objects. A high efficiency of over 50% is possible in the resonant operation, when transmitter and receiver are not too far apart. As a rule of thumb is that the distance should remain under the one-to two times the diameter of the larger coil. Furthermore, the size difference of the two coils should not significantly exceed a factor of 3 to 4. Typically, the efficiency of coil systems, coil ranging from 60% to 70 % for simple systems with low power to 97 % at 10 kW and 15 cm and about 50 cm diameter coil.
Further technical details can be found at inductive power transfer.
Capacitive energy transfer
Principle
A system for capacitive energy transfer consists of the following components: two electrically conductive surfaces forming transmitter electrodes. The areas are arranged next to each other ( co-planar ), and usually at the surface an electrically insulating layer. At these electrodes, an alternating electric potential is applied, the potential of the two electrodes having respectively different polarity. The receiver includes two corresponding electrodes which are brought each face to face in the vicinity of the transmitter electrode. But this case, the receiver electrodes remain of the transmitter electrode electrical isolation. In each case, a transmitter and a receiver electrode to form a surface condenser, respectively. When the two receiver electrodes are connected through an electrical load, a current circuit consisting of a series circuit the two capacitors and the load surface is formed like this. Because of the alternating electric potential now can flow an AC and it will transfer power.
In the area of data transfer and low power, there are systems with only one explicit transmitter and receiver electrode. The circuit is closed at this over the fringing electric fields between the transmitter and receiver, even at best, about the stray fields between the respective mass - surfaces here.
Frequency range
, The frequency range normally used is from 100 kHz up into the MHz range. In this frequency range the spread plays no role as an electromagnetic wave for the application and the calculations are done assuming a quasi-static electric field and of concentrated replacement components.
Resonance operation
Conventionally used in the receiver or in the transmitter, one or more resonant coils forming the surface capacitors form a resonant circuit (or resonant circuit ). Depending on the tuning of the resonant circuit can be used to:
- To maximize the transmitted power,
- Adjusted by varying the frequency of the transmitted power,
- Adjust the required load characteristics of the transmitted power,
- Match the impedance of the transmitter coil to the requirements of the AC generator,
- To achieve a filtering effect to suppress higher frequency components of the generator.
Usually is to maximize the power transmitted in the foreground. In the resonance frequency of the coil compensates for the complex impedance of the two capacitors, thus enabling a power transmission with a substantially lower voltage generator. An increase in efficiency due to resonance is only possible through any second-order effects.
Efficiency
Losses occur in the supply lines and electrodes and resistive losses in the insulating layer as a dielectric loss and in the resonant mode in the resonant coil. With the use of well-conducting electrodes and a low-loss dielectric, a efficiency of about 90% can be achieved.
Electromagnetic energy transfer
Principle
For electromagnetic energy transfer electromagnetic waves are used. The principle corresponds to the transmission of radio signals. The distance between transmitter and receiver is large enough that the wave properties of the electromagnetic fields are relevant and may be used. As a transmitter as well as receiver antennas such as dipoles or other antenna types, especially with directivity used.
Frequency range
It can be used MHz to GHz range frequencies in the upper 100. Some systems use the same frequency bands such as the GSM mobile communications technology, and the transmitter and receiver uses compatible, but at shorter distance than communication.
Properties
Unlike quasi-static inductive and capacitive systems occur here real radiation losses. The generated electromagnetic waves propagate from the source and carry energy with them. Wave components, which are not used by the recipient, will be lost. This particular transmitter systems without directivity are very inefficient. Furthermore, the generation of relatively high frequencies in the transmitter and the receiver is in rectified efficient than at lower frequencies as in the quasi-static systems. By directionality but greater distances than in the quasi-static system can be bridged by a few meters, and the efficiency ( low level ) is better. However, objects within the transmission path can then cause a strong attenuation and negate the power transfer.
Energy transfer by laser
Principle
For the energy transfer is a directed light beam, preferably used in the infrared range. To an infrared laser is used. The light beam is directed to a photocell in the receiver, which converts the light into electrical energy.
Properties
The actual energy transfer occurs very focused, so this little energy is lost. However, the conversion of electrical energy into light and vice versa with low energy efficiency. Although for the conversion of electric energy into infrared - light infrared semiconductor laser (for example, with a surface of the emitter ), the best conversion efficiency of all light sources, the efficiency is still only in the region of 50%. The best efficiency of a solar cell has recently been reported at 28.2 % (under standard conditions). Concentrated infrared light allows a slightly higher efficiency policy. More than 20% efficiency is expected to be unlikely for the whole transmission chain. The transmitter must have a good and accurate detection of receivers and be able to position its laser beam exactly. In particular, moving objects, this is a big challenge. To transfer benefits of a few watts, the laser beam must be so strong that it is dangerous. He can then easily cut through, for example, living tissue. Therefore, an accurate and very fast recognition and must be switched off when objects come within range of the laser beam.
Availability
The American start -up company Power Beam 2007 has presented a prototype and a corresponding patent. In the meantime, the company has terminated, however, the former employees offer their knowledge but other interested parties to.
Developments
Wireless energy transfer is not new. A hundred years ago it was possible Nikola Tesla to transmit electrical energy through the air.
Since 2004, the German project KONTENDA working on the development of a technique for non-contact transmission of electrical energy for industrial applications.
In August 2008, was introduced by Intel Corporation a Wireless Resonant Energy Link ( wrel ).
Electric toothbrushes with built-in battery use over a few millimeters energy transfer through the housing by means of a resonant transformer. The resonant transformer, typically the resonant frequencies in the range of 100 kHz, this is by several millimeters wide, " air gap", which forms the housing, and in correspondingly large leakage fluxes, whereby the efficiency is reduced in the transfer of energy between the charging station and toothbrush.
A working group at the Massachusetts Institute of Technology (MIT) called her wireless energy transmission system as " WiTricity ", this brand is marketed commercially by an eponymous company.
Standards and norms
For wireless energy transfer, there are a few standards and norms. The previously existing relate solely to inductive power transfer.
Mobile devices
Mainly for use in the field of mobile devices, there are essentially three standards, which have a certain distribution: the Qi standard of the Wireless Power Consortium ( WPC), which Rezence technique the Alliance for Wireless Power ( A4WP ) and in so-called "Power Mats " used Powermat charging technology of the Power Matters Alliance ( PMA).
Qi
On 17 December 2008, the International Wireless Power Consortium (WPC ) was established that the introduction of a global standard called Qi ( Chinese word for " life energy", pronounced: [ tʃi ː ] ) envisaged for charging of electronic products. Among the 82 members of the Wireless Power Consortium include market leaders in mobile phones, consumer electronics, batteries, semiconductors, components, wireless power technology and infrastructure such as network operators, furniture manufacturers and suppliers. Since mid-2010 there is the industry standard Qi, for inductive energy transmission to mobile devices to 5 W. Numerous Qi chargers have since appeared on the market and some are offered in multiple improved versions, so this standard has now been overcome probably the largest children's diseases.
Power Mats
The Power Matters Alliance, formed among others by Procter & Gamble and Powermat Technologies in March of 2012 supports a standard developed by Powermat Technologies also for inductive charging of devices. However, to date there are no devices that have the technology built directly themselves, but here appropriate chargers and batteries are sold, which are used in the respective devices. The Powermat technology is prominent on the supply side by the fact that Starbucks and McDonalds stores charging options are available in various.
Rezence
The first " wireless power" and now " Rezence " technology dubbed the Alliance for Wireless Power is in contrast to the other two standards are not on induction, but on a resonant magnetic coupling; it promises to be, inter alia, also reduce the susceptibility to interference, quite a large range and charging strengths up to 20 W, which could also allow the wireless charging of small laptops. In the Alliance for Wireless Power to various industrial companies, including Intel, Qualcomm, Samsung, Broadcom and IDT Corporation have joined forces.
Convergence of Powermat technology and Rezence
In February 2014, the hitherto competing consortia AWWP and PMA have announced to provide greater interoperability in wireless charging, by making them compatible with each other's. For this purpose involves the PMA receive the Rezence technology in their standard, and the A4WP added as an option for inductive charging Powermat technology into their sake specification.
Electric vehicles
In the DKE there is the working group AK 353.0.1 who created the end of 2010 a draft application rule for inductive charging of electric vehicles. The design is currently (July 2011) still in the comment period.
Emission of electromagnetic fields
There are currently no explicit standards and standards for the emission of electromagnetic fields of contactless power transfer systems known. However, the general, and adapted for the respective product groups, standards and standards for electromagnetic compatibility ( EMC) and electromagnetic effects on users ( EMF), which are observed and applied apply. For EMF, there is in particular the limits of ICNIRP, are the basis for many local standards.