Wireless Power Transmission

INTRODUCTION
 Wireless power transfer (WPT), wireless power transmission,
wireless energy transmission (WET), or electromagnetic power
transfer is the transmission of electrical energy without wires
as a physical link. In a wireless power transmission system, a
transmitter device, driven by electric power from a power
source, generates a time-varying electromagnetic field, which
transmits power across space to a receiver device, which
extracts power from the field and supplies it to an electrical
load. The technology of wireless power transmission can
eliminate the use of the wires and batteries, thus increasing
the mobility, convenience, and safety of an electronic device
for all users.
 Wireless power transfer is useful to power electrical devices
where interconnecting wires are inconvenient, hazardous, or
are not possible.
CONTENTS
 What in WPT?

 The transmission of energy from one place

to another without using wires.
 Conventional energy transfer is using wires
 But, the wireless transmission is made
possible by using various technologies.
Why not wires?
 As per studies, most electrical energy transfer is
through wires.
 Most of the energy loss is during transmission
 On an average, more than 30%
 n India, it exceeds 40%
 Why WPT?
 Reliable
 Efficient
 Fast
 Low maintenance cost
 Can be used for short-range or long-range.

 HISTORY
 Nikola Tesla in late 1890s .Pioneer of
induction techniques his vision for “World
Wireless System” The 187 feet tall tower to
broadcast energy. All people can have
access to free energy due to shortage of
funds, tower did not operate Tesla was able
to transfer energy from one coil to another
coil He managed to light 200 lamps from a
distance of 40km The idea of Tesla is taken
in to research after 100 years by a team led
by Marin Soljačić from MIT. The project is
named as WiTricity
ENERGY COUPLING
 The transfer of energy
 Magnetic coupling
 Inductive coupling
 Simplest Wireless Energy coupling is a transformer

TYPES AND TECHNOLOGIES OF WPT

 Near-field techniques
 Inductive Coupling
 Resonant Inductive Coupling
 Air Ionization
 Far-field techniques
 Microwave Power Transmission (MPT)
 LASER power transmission
INDUCTIVE COUPLING
 Primary and secondary coils are not connected with
wires.
 Energy transfer is due to Mutual Induction

Transformer is also an example Energy transfer

devices are usually aircored Wireless Charging
Pad(WCP),electric brushes are some examples On a
WCP, the devices are to be kept, battery will be
automatically charged.
Electric brush also charges using inductive
coupling.The charging pad (primary coil) and the
device(secondary coil) have to be kept very near to
each other It is preferred because it is comfortable.
Less use of wires Shock proof.
Resonance Inductive Coupling(RIC)
 Combination of inductive coupling and resonance.
 Resonance makes two objects interact very strongly.
 Inductance induces current.

How resonance in RIC?

 Coil provides the inductance
 Capacitor is connected parallel to the coil
 Energy will be shifting back and forth between
magnetic field surrounding the coil and electric
field around the capacitor
Radiation loss will be negligible
An Example
Block Diagram of RIC
WiTricity
 Based on RIC
 Led by MIT‟s Marin Soljačić
 Energy transfer wirelessly for a distance just more than 2m.
 Coils were in helical shape
 No capacitor was used
 Efficiency achieved was around 40%

WiTricity… Some statistics

 Used frequencies are 1MHz and 10MHz
 At 1Mhz, field strengths were safe for human
 At 10MHz, Field strengths were more than ICNIRP
standards
 WiTricity now…
 No more helical coils
 Companies like Intel are also working on devices that make use of
RIC
 Researches for decreasing the field strength
 Researches to increase the range.
 RIC vs. inductive coupling.
 RIC is highly efficient
 RIC has much greater range than inductive coupling
 RIC is directional when compared to inductive coupling
 RIC can be one-to-many. But usually inductive coupling is one-to-
one
 Devices using RIC technique are highly portable.
Air Ionization
 Toughest technique under near-field energy transfer techniques
 Air ionizes only when there is a high field
 Needed field is 2.11MV/m
 Natural example: Lightening
 Not feasible for practical implementation
 Advantages of near-field techniques
 No wires
 No e-waste
 Need for battery is eliminated
 Efficient energy transfer using RIC
 Harmless, if field strengths under safety levels
 Maintenance cost is less
Disadvantages
 Distance constraint
 Field strengths have to be under safety levels
 Initial cost is high
 In RIC, tuning is difficult
 High frequency signals must be the supply
 Air ionization technique is not feasible
 Far-field energy transfer
 Radiative
 Needs line-of-sight
 LASER or microwave
 Aims at high power transfer
 Tesla‟s tower was built for this
Microwave Power Transfer(MPT)
 Transfers high power from one place to another. Two places being in line of sight usually
 • Steps:
 Electrical energy to microwave energy.
 Capturing microwaves using rectenna.
 Microwave energy to electrical energy.
 AC can not be directly converted to microwave energy
 AC is converted to DC first
 DC is converted to microwaves using magnetron
 Transmitted waves are received at rectenna which rectifies, gives DC as the output
 DC is converted back to AC
 LASER transmission
 LASER is highly directional, coherent
 Not dispersed for very long
 But, gets attenuated when it propagates through atmosphere
 Simple receiver

Photovoltaic cell
 Cost-efficient
Solar Power Satellites (SPS)
 To provide energy to earth‟s increasing energy need
 To efficiently make use of renewable energy i.e., solar energy
 SPS are placed in geostationary orbits
 Solar energy is captured using photocells
 Each SPS may have 400 million photocells
 Transmitted to earth in the form of microwaves/LASER
 Using rectenna/photovoltaic cell, the energy is converted to electrical energy
 Efficiency exceeds 95% if microwave

 Rectenna
 Stands for rectifying antenna
 Consists of mesh of dipoles and diodes
 Converts microwave to its DC equivalent
 Usually multi-element phased array
  Rectenna in US
 Rectenna in US receives 5000MW of power from SPS
 It is about one and a half mile long

Other projects
 Alaska‟21

 Grand Bassin
 Hawaii

LASER vs. MPT

When LASER is used, the antenna sizes can be much smaller
Microwaves can face interference (two frequencies can be used
for WPT are 2.45GHz and 5.4GHz) LASER has high attenuation
loss and also it gets diffracted by atmospheric particles easily.
Advantages of far-field energy
transfer
 Efficient
 Easy
 Need for grids, substations etc are eliminated.
 Low maintenance cost.
 More effective when the transmitting and receiving points are along a
lineof- sight.
 Can reach the places which are remote.
 Radiative
 Needs line-of-sight
 Initial cost is high
 When LASERs are used,
 ◦ conversion is inefficient
 ◦ Absorption loss is high
 When microwaves are used,
 ◦ interference may arise
 ◦ FRIED BIRD effect 8/31/2010
APPLICATIONS
 Near-field energy transfer
 Electric automobile charging
 Static and moving
 Consumer electronics
 Industrial purposes
 Harsh environment
 Far-field energy transfer
 Solar Power Satellites
 Energy to remote areas
 Can broadcast energy globally (in future)
 CONCLUSION

 Transmission without wires- a reality

 Efficient
 Low maintenance cost. But, high initial cost
 Better than conventional wired transfer
 Energy crisis can be decreased
 Low loss
 In near future, world will be completely wireless.