project16 presentation
DESCRIPTION
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WIRELESS POWER TRANSFER
By: David Chavez and Shu-Hui Cheng
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Introduction• Wireless Power Transfer System will help eliminate the
clutter of outlets.
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Benefits and Features
Benefits• Wireless transmission of electricity
• Eliminate power cords• Safe wireless power transfer
• Smart charging• Environmental friendly charger• Charging stops automatically when the battery is fully charged• Charging begins automatically when the battery level drops below a threshold value
• Compatibility with USB devices• Support for wide range of devices
Features• Ability to do wireless power in a small range
• Automatic detection of battery life and the need for charging
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Wireless Power Transfer System
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Battery Detection Communication
Wireless Transmission
System Overview
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USB
Edge detector
Battery Indicator
SR Latch
Voltage Regulator
Rectifier
Receiving Antenna Coil
Original Charging Annex Block Diagram
Device
Switch
Sine Wave Generator
Ultrasound transmitter
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USB
PIC Microcontroller
Hall effect sensor
Ultrasound
Voltage Regulator
Rectifier
Receiving Antenna Coil
Clock Oscillator
Charging Annex Block Diagram
Device
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Ultrasound Receiver
Bridge Rectifier
Amplifier
Transmitting Antenna Coil
Amplifier
Oscillator
Voltage Divider
AC to DC power Supply
Voltage Regulator
Original Charging Platform Block Diagram
Low Pass Filter
Switch
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Ultrasound
Bridge Rectifier
Amplifier
Transmitting Antenna Coil
Amplifier
Oscillator
Voltage Divider
AC to DC power Supply
Switch
Charging Platform Block Diagram
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Hardware Overview• Power Supply
• Takes 120V from wall outlet and converts to 5Vdc to power components
• Also converts the 5Vdc to an amplified 30V for power transmission.• Battery Detection
• Reads current flowing into battery and sends signal to continue charging if current is high
• Recieves ultrasonic signal and powers on MOSFET to transmit power.• Loop Antenna
• Receives 13.5MHz signal and transmits it through a loop antenna.• Battery Charger
• Takes 13.5MHz signal and converts to stable 4.2Vdc voltage to charge battery.
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Battery Detection• Encountered a few
problems with initial design
• New design comprised of two main components• Hall Effect Sensor• PIC 16F887
Battery Level (%) Line Current (A)Past 95 ≈0.05
95 0.25
90 0.35
75 0.6
70 0.7
0 0.85
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Battery Detection• Reads current flowing into
the battery.• Can be connected to any
Mini USB device• Outputs 50% 5Vpp PWM
Signal to Ultrasound• Receives Ultrasound signal
and turns on MOSFET
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PIC16F887 Flow Chart
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3.5cm
Antenna Coil Pair
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RF Power Transmission using Antenna Coil Pair
Parallel LC resonant circuit
System architecture
• Oscillator: Generate a sinusoidal signal at 13.5 MHz
• Power Amplifier: Amplify signal to increase transmission range
• Balun: Convert the unbalanced signal to a differential signal (because the antenna coil is a balanced structure - no definite ground)
• Antenna coil: Convert the electrical signal to magnetic field (vice versa)
• Bridge rectifier: Down convert the AC signal to DC
• Voltage regulator: Stabilize DC voltage
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RF Power Transmission Principle• Based on Faraday’s Law of Induction:
• At the transmit coil, a time-varying current generates a time-varying magnetic field• The time-varying magnetic field induces a time-varying current on the receive coil
• Testing for two coil antennas
• To maximize the power transmission efficiency, the coil must be tuned to the operating frequency
• The coil is brought to resonance at 13.5 MHz by adding a capacitor in parallel• Resonance frequency testing
where(the radiated field has a cubic roll-off)
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System Demo
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Measurement Results (Transmitter side)Oscillator output:
1.77 Vpp @13.48 MHz
1st amplifier output:4.44 Vpp
2nd amplifier output:12.74 Vpp
Balun output (fed to transmit coil):33.4 Vpp
8 dB gain 9.2 dB gain
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Measurement Results (Receiver side)Receive coil output:7.94 Vpp @13.48 MHz
Bridge rectifier output:
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Measurement Summary• Range
• Power transmission efficiency = Received output from coil / transmitted output from coil = 6.8 %
• System efficiency = Power drawn from AC supply / power received to USB = 6.6 %
Distance between Two Coil (cm) DC Voltage (V) to the USB
Closest~0.1 4.17
1 2.88
2 1.26
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0 1 2 3 4 5 6 7 80
5
10
15
20
25
30
35
40
Voltage (V)
Testing for Two Coil Antennas
Distance (cm)
• Measured peak-to-peak voltage at the receive coil antenna as separation distance increases
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12.5 13 13.5 14 14.5 15 15.50
50
100
150
200
250
300
350
Frequency(MHz)
Voltage (m
V)
Resonance Frequency Testing• Measured peak-to-peak voltage at receive coil as the frequency changes • Confirm the coil resonates at 13.5 MHz
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Battery Detection System testingPWM signal from output of PIC and Ultrasound receiving signal
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Battery Detection System testingRectified Ultrasound signal in range
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Battery Detection System testingAmplifier Signal In Range
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Battery Detection System testingAmplifier Signal Out of Range
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Battery Detection Recommendation • To properly transmit the Charging signal the ultrasound
needs to be in relative line of sight.• Ultrasound creates cone like region of detection• Reassure sufficient power to PIC
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RecommendationsMultilayer coil
• Reduce the size of the coil• Can be made planar for easy integration with device platform
Ferrite loading• Loading the coil with ferrite to concentrate the magnetic field so as to increase range
Impedance matching • Amplifier requires 50 input and output impedance for maximum power transfer• Impedance matching circuit constructed by discrete L and C elements may be inserted between the
balun and the output of the final stage amplifier
Range improvement• Insert more RF power amplifiers• Current amplifier after voltage regulator
Battery detection improvement• Output battery level from cell phone’s operating system
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•Successes• The communication part with ultrasound work• Battery detection through current can be adjusted to
needed current• Wireless transmission part can transfer power from
annex to platform and light up an LED
•Challenges• Charging platform needs more power from
transmission• The Range for power transmission
Successes and Challenges
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Future Work• Improved loop antenna design
• Get antenna made professionally• Different shape may increase range
• Two AC-DC power converters to be able to transmit more power
• Add more devices to single dock
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SWOT Analysis• Strengths
• Reduce outlet clutter• No need to remember to
charge
• Weakness• Charge range limited• Efficiency
• Opportunities• Regular Household• Offices
• Threats• Transformer style designs• Similar Projects (WiTricity)
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• With this responsibility, not only will we reassure that the final product will meet its expectations, we will assure it is safe for use and put warning labels on items deemed unsafe if tampered with
• Through thorough testing of each component, we will guarantee that our performance claims are accurate
• Ideally this project will further open the door to exploration in wireless power transfer.
Ethnical Considerations
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Acknowledgements
Professor Jonathan MakelaRyan May
Parts Shop Staff
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Thank you and Questions?