Post on 03-Jan-2016
description
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Wireless power for mobile phones -
System overview
Nov 25, 2012V1.1
System overview
Rx
Tx
• Embedded in mobile device• After market case/dongle
connected through the power connector
• Add-on connected through dedicated WLC pins
• Embedded in furniture/car/infrastructure
• After market mat
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Resonance circuit & power driver
Power Source
TXCoil
RXCoil
ControlUnit
Demodulator
Matching circuit & Rectifier
ControlUnit
Modulator
DC/DCCommunication
Power
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Block diagram
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Tx-Rx coils
Electric current flowing in a wire gives rise to a magnetic field around it.Alternating the current will alternate the magnetic field
Shaping the wire as a loop will band that field in a “lung” shape.
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Tx-Rx coils – Magnetic induction basics
Figures: http://ipodphysics.com/magnets-loop-or-coil.phpt
Figure 1: http://www.electrical4u.com/what-is-transformer-definition-working-principle-of-transformer/ Figure 2: http://makezine.com/2013/11/04/component-of-the-month-transformer/ Figure 3: http://www.britannica.com/EBchecked/media/1355/Magnetic-field-B-of-two-current-loops-with-currents-in
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Tx-Rx coils – Magnetic induction basics
Wireless power system is an air core transformer between planar coils one on top of the other.
Energy coupling means that an energy source has a mean of transferring its energy to a second object. Transformers may use iron core to deliver the magnetic flux
Single coil– Most common designPros – chip and easy solution / Cons – difficult alignment
Fig1:http://www.qitah.com/blog.htmlFig2:http://phys.org/news203691107.htmlFig3:http://patentimages.storage.googleapis.com/US20130119773A1/US20130119773A1-20130516-D00015.png
Large Tx coil – Common in loosely coupled systemsPros – easy alignment / Cons – difficult design and tune
Array of small Tx coil – One or more coils provide power simultaneouslyPros – easy alignment / Cons – Cost of coils and drivers
3 coil array – Only one coil provides power at a timePros – easy alignment / Cons – Cost of coils and drivers
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Tx-Rx coils – Coil designs
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Resonance circuit and power driver
Power driver Resonance circuit
Figure 1: HIGH EFFICIENCY LOOSELY COUPLED WIRELESS POWER TRANSFER SYSTEM VIA MAGNETIC INDUCTION By ZHEN NING LOW
Resonant circuit - Determines the self resonance frequency of the Tx,Mainly influenced by the coil and the resonance capacitors.
Power driver - pushes the current to the resonance circuit in different frequencies around the self resonance
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Resonance circuit and power driver
Figure 1: http://perlgeek.de/blog-en/perl-6/rakudo-memory-leaks.html10
Resonance circuit
• The overall impedance the driver “sees” when modeled as a series RLC circuit
• At the resonance frequency the capacitive and inductive impedance equals
The driver then sees resistive only minimum overall impedance and the power delivery to the Rx is maximal
• The resonance curve changes with each different : Rx design (EE & ME) Phone material Misalignment from the center Variation during manufacturing Load drawn
Frequency
Ampl
itude
Frequency control – the driver changes the frequency along the resonance curve Control becomes difficult when Q is high & at resonance control is unstable Frequency range shall be dynamic due to curve changes Passing to the second side of the peak may reverse the control rules
Frequency
Ampl
itude
Other methods of control:Voltage control – increasing the input voltage will increase the current through the coil and the transmitted powerPulse width control – increasing the on time of the signal will increase the transmitted power
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Driving the power
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Data modulation
Power driver
Modulator
Demodulator
Matching circuit & Rectifier
load modulation - •Rx modulates the operational frequency by short circuiting the coil to a secondary load•The secondary load changes both the load of the Tx and the resonance curve•The demodulator sense the change in voltage, current or phase between them on the operational frequency
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Data modulation
Example of voltage change at the Tx
Example of phase change at the Tx
Signals in reality may vary a lot from the simulation presented….14
Data modulation
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Questions? Comments? Remarks?
Thanks,Rotem Shraga
(shraga.rotem@gmail.com ; 052-6443944)Figure: http://www.fodrizzle.com/wp-content/uploads/2012/02/funny-birds-wire-drawing.jpg
It’s called wireless power, it’s the future