WIRELESS TRANSFER OF ELECTRICAL ENERGY
Flemming Nyboe, Danish Technological InstituteLars Lading, Sense A/S
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
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
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
Why Wireless?
Wires are inconvenient and expensive
Connectors have a relatively high likelihood of faults
Mobile devices
Environmental conditions
Access
Pollution
The vision
Small autonomous devices receive wireless energy already many commercial products but still limited uses
Large devises (automobiles) may be
Energy distribution - unlikely
Nikola Tesla (1856-1943)
A global system for "the transmission of electrical energy without wires proposed 1904
Wardenclyffe Tower
Tesla did discover essential concepts, but may also have invoked unreal physics (?)
Classification
Propagating E-M waves
Near field
Resonant coupling (Q = 1/k)
Dont forget conduction
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
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
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
Dries van Wageningen and Eberhard Waffenschmidt, Philips Research
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!
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
APPLICATIONS
Charging mobile phones
Convenient Power solution
Dells solution
Charging cars
Nissan concept
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
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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