wireless transfer of electrical energy
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WIRELESS TRANSFER OF ELECTRICAL ENERGY
Flemming Nyboe, Danish Technological InstituteLars Lading, Sense A/S
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Topics
Wireless in nature
The vision (get rid of all the wired connections)
Tesla + +: ideas, initiatives and failures the history
Basic relations and limitations
Reality : Many applications are emerging, several commercial companies
Examples Charging of small electronic devices Charging of large electronic devices
A demonstration and the work at TI
Safety and standards
Outlook
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Wireless in Nature
Wireless transfer of energy is by far the dominating way of energy transfer
Also energy to the world is dominated by wireless solar energy: Solar energy: about 174 petawatts (30% reradiated)
Geothermal: 44.2 terawatts
Tidal energy: 3 terawatt
Global consumption: 15 terawatt
Blackbody radiation accounts for a considerable amount of energy tranfer
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Wireless energy vs. Wireless information
Wireless information: Energy efficiency is very (extremely) low - down to 10-20
Wireless energy transfer: Must be >> 0.1 to be viable
Broadcasting methods are not feasible
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Why Wireless?
Wires are inconvenient and expensive
Connectors have a relatively high likelihood of faults
Mobile devices
Environmental conditions
Access
Pollution
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The vision
Small autonomous devices receive wireless energy already many commercial products but still limited uses
Large devises (automobiles) may be
Energy distribution - unlikely
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Nikola Tesla (1856-1943)
A global system for "the transmission of electrical energy without wires proposed 1904
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Wardenclyffe Tower
Tesla did discover essential concepts, but may also have invoked unreal physics (?)
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Classification
Propagating E-M waves
Near field
Resonant coupling (Q = 1/k)
Dont forget conduction
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Propagating E-M waves
Electric and magnetic fields are coupled: If one is eliminated (e.g. electric field by a conductor) the propagation ceases
Diffraction Transmitter and receiver must be
much larger than the wavelength
Far field divergence
Focusing:
Propagation in empty space
Conducting media is a problem (metal, water)
/ sourced
argsource t etd d
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Near Field Coupling
Range < /4
E and M are not coupled e.g. coupling through conducting media (human body) is feasible
Some radiation will also be present (often negligible)
The basis for transformers (inductive) and capacitors (electric/capacitive), used e.g. inductive cookers
Coupling coefficient k < 1; wireless coupling may be defined by cases where k < 0.2
? Is a high coupling efficiency compatible with a low k
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Resonant Coupling
A low coupling coefficient does not necessarily imply a low coupling efficiency!
Resonant coupling may provide for efficient transfer of energy between weakly coupled systems: Q 1/k
Ohmic loses sets a limit; undesired couplings may also pose a problem; radiation losses at higher frequencies
Resonant coupling is well known in mechanical systems
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Dries van Wageningen and Eberhard Waffenschmidt, Philips Research
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Overall power budget
Generally positive for small autonomous devices according to Prof. Ron Hui, Director, Center for Power Electronics City University of Hong Kong 21 August 2009 can be questioned!
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History1893 Tesla demonstrates the wireless illumination of phosphorescent lamps
1917: Tesla's Wardenclyffe tower is demolished
1964: Brown demonstrates a model helicopter that received all the power needed for flight from a microwave beam
1971: Prof. Don Otto develops a small trolley powered by induction at The University of Auckland, in New Zealand
1973: World first passive RFID system demonstrated at Los-Alamos National Lab.[
2007: Prof. Marin Soljai et al, at MIT, wirelessly power a 60W light bulb with 40% efficiency at a 2 metres distance with two 60 cm-diameter coils
2008: Bombardier offers new wireless transmission product PRIMOVE, a power system for use on trams and light-rail vehicle
2009: Sony shows a wireless electrodynamic-induction powered TV set, 60 W over 50 cm
2009: Wireless Power Consortium formed (www.wirelesspowerconsortium.com)
2010: Multiple coil system for implants demonstrated with 82% efficiency
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APPLICATIONS
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Charging mobile phones
Convenient Power solution
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Dells solution
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Charging cars
Nissan concept
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Koreas
Korea Advanced Institute of Science and Technology
Three busses runs in an amusement park 400 m of charging lane
70% efficiency
20% of the roadway needs power strips
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Conclusion for this part
The basic physics is well established
Technology well in place for small devices (< 5 W)
Automobile charging?
Adaptive systems?
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