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?