Final Year Project: Wireless Power Transfer For Mobile Phone Kong Chin Hung D Supervisor: Dr. Wei-Nong FU

Objective  Designing a wireless charger to charge mobile phone by resonant inductive coupling.  Designed to test and verify the theoretical method of wireless charging.  Get the acceptable efficiency of wireless power transfer.  The technology (PWM, full-bridge inverter, buck converter, full wave rectifier and USB port)

Chapter 1. Introduction

 14,000,000 mobile phones in Hong Kong  Large demand for chargers  conductive traditional charger  Inconvenient to the disabled  Messy wire  damage to charging plug  The need for wireless charger Why need wireless charger?

Three major keys in wireless power transfer

Flow chart of the project

Chapter 2. Resonant wireless power transfer

Skin effect  High frequency operation: 100KHz (from Arduino UNO R3 )  Litz wire  reduce skin effect Skin effect

Effect of high frequency Higher frequency  lower skin effect 100kHz

Switching loss  transistors and diodes  turned on and off  losses I & V waveforms produce overlapping switching losses Losses increase with the increase of frequency  hard switching At the switch-on, I rises and V drops At the switch-off, V rises and I declines

Chapter 3. Analysis of technology, design and implementation of circuits

Diode selection  high frequency  the recovery time of the diode is important factor of the transfer efficiency  Schottky diode rectification efficiency measurements  operation will be satisfactory up to several megahertz

DC-AC full bridge inverter Current flow when full-bridge inverter is operating full-bridge’s drive energy is twice of the half-bridge

Efficiency of the inverter rms voltage (V) rms current (A) phase angle (degree) Power (W) Input12V0.723A/8.676W Output10.86V0.939A34.56 ° 8.398W Efficiency = 8.398/8.676 x 100% = % Actual total power loss in inverter = 0.278W

Gate Drive circuit  Driver chip- IR2110 with MOSFET IRF540  Can operate at 500 kHz  Full circuit of full bridge inverter

Full wave rectifier  transforming AC voltage to DC voltage all negative voltage can be rectified to positive

Ripple voltage after adding a capacitor Smoothing Capacitor By Capacitor = 330uF To increase the average output voltage and minimize the ripple voltage The ripple voltage has been minimized to 480mV in 100 kHz operation

Buck Converter  DC to DC buck converter  step down voltage to 5V  a feedback loop to detect V out  adjust the duty cycle  LM2675-adj with feedback loop circuit

USB Port (standard A) Configuration of USB 1A charging circuit connect the wireless charging receiving circuit to the mobile phone 4 pins

Chapter 4. Pulse-width modulation (PWM) controller for full-bridge inverter  Two PWM signals are required  PWM 2 signal which is anti- phase with PWM1 output

Chapter 5. Experiment for coil

Experiment 1 -- testing for coil material Wire Type 1 wire Type 2 wire No. of wire per bunch 850 Diameter of each wire0.38mm 0.25mm two pair of flat spiral coil with outer radius 75mm, inner radius 25mm, and 16turns

Experiment 1 result rms voltage (V) rms current (A) Phase angle (degree) Power factor Power (W) Tx Rx Efficiency32.29% Type 1 wire rms voltage (V) rms current (A) Phase angle (degree) Power factor Power (W) Tx Rx Efficiency51.63% Type 2 wire ✔ type 2 wire

Experiment 2 – Relationship between efficiency and coil distance Distance (cm)Efficiency (%) Closer distance, Higher efficiency

Experiment 3 – Relationship between efficiency and coil displacement Displacement (cm)Efficiency (%) two coil were only 50% coupling  efficiency dropped to nearly 0%

Experiment 4 -- Feasibility for using a bigger panel (Tx) rms voltage (V) rms current (A) Phase angle (degree)Power factor Power (W) Tx Rx Efficiency1.12% Tx: 18cm radius, 6 turns Rx: same rms voltage (V) rms current (A) Phase angle (degree)Power factor Power (W) Tx Rx Efficiency1.87% Tx: flat spiral coil with 18cm outer radius, 9.5cm inner radius, 16turns Rx: same large leakage magnetic field  low efficiency

Chapter 6. Problem Encountered 1.The reverse of the current probe cause measured phase angle >90degree, power factor is negative 2.Wrongly connecting GND led to short circuit 3.unable to measure the efficiency of coil by using the signal generator 4.The noise will be very large if the coil is not well-constructed 5.In high frequency, jump wires under circuit board produces a lot noise

Chapter 7. Future Development  Safety issue  A bigger charging panel  Surface-mount technology  Size of receiver

Chapter 8. Conclusion  nearly 50% efficiency  eliminates the risk of short circuit during charging  Apply to other low power devices by making only a little modification  works by using resonant inductive coupling  transmitter is stored in a plastic box