12-09-2014, 04:40 PM
Wireless Power Transmission Using Magnetic Resonance
Wireless Power.pdf (Size: 1.07 MB / Downloads: 125)
INTRODUCTION
Our project was based upon a MIT published paper in the year 2007 titled
“Wireless Power Transfer via Strongly Coupled Magnetic Resonances” [1]. The
project was researched by former Cornell students Lucas Jorgensen and Adam
Culberson in the year 2008 [2].
During the course of this research, we investigated the need and usefulness of
wireless power transmission and the feasibility of using magnetic inductive
coupling as the means for wireless power transmission. The paper will outline our
design process and the logical steps we took in the experimentation and design of
our circuits. The first section of the document will explicitly illustrate the goals
we set to accomplish during the allotted time frame of three and a half weeks.
With the complexity of the problem in mind and what we must accomplish, our
team began research on the available means to transmit power without a physical
connection.
THEORITICAL BACKGROUND
The principle of Evanescent Wave Coupling extends the principle of
Electromagnetic induction. Electromagnetic induction works on the principle of a
primary coil generating a predominantly magnetic field and a secondary coil
being within that field so a current is induced within its coils. This causes the
relatively short range due to the amount of power required to produce an
electromagnetic field. Over greater distances the non-resonant induction method
is inefficient and wastes much of the transmitted energy just to increase range.
This is where the resonance comes in and helps the efficiency dramatically by
"tunneling" the magnetic field to a receiver coil that resonates at the same
frequency
INTENDED GOALS
Our primary goal was to be able to wirelessly transfer power (in watts) of an AC
oscillating waveform into a DC voltage on the receiving end, which could be used
to power an electrical load (in watts) to demonstrate instantaneous power transfer.
To do this, we intended to design a tunable oscillator capable of generating
frequency in the RF band (1MHZ – 20 MHz) and a power amplifier to supply
enough power to be transmitted for powering the electrical load. In addition to
this, we also intended to demonstrate the evanescent waves by the illustration of
an exponential relationship of power transmitted to the receiver as a function of
distance of separation between the receiver and transmitter coils.
SYSTEM DESIGN
With all the necessary background research completed it became clear what basic
design components the entire system would require. First we needed a method to
design an oscillator, which would provide the carrier signal with which to
transmit the power. Oscillators are not generally designed to deliver power, thus it
was necessary to create a power amplifier to amplify the oscillating signal. The
power amplifier would then transfer the output power to the transmission coil.
Next, a receiver coil would be constructed to receive the transmitted power.
However, the received power would have an alternating current, which is
undesirable for powering a DC load. Thus, a rectifier would be needed to rectify
the AC voltage to output a clean DC voltage. Finally, an electric load would be
added to complete the circuit design
DESIGN DETAILS
The challenges encountered during the design of the oscillator were the selection of
the oscillator design and the Op-Amp chip required to produce a stable and
symmetrical oscillating signal. We had experimented with IC Logic chips and low
frequency response Op-Amp chips for the design of the oscillator. However, the
oscillation signal output from these circuit configurations was not stable or
symmetrical. We also initially had problems with distortion of the signal by the
unstable power supply from the PCB board and other extraneous noise at high
frequencies. We dealt with this problem by neatly laying out the relaxation oscillator
circuit using shorter wires and the placing two decoupling capacitors of one
microfarads each between the positive and negative power supply to the ground.
POWER AMPLIFIER
In order to generate the maximum amount of flux which would induce the largest
voltage on the receiving coil, a large amount of current must be transferred into the
transmitting coil. The oscillator was not capable of supplying the necessary current,
thus the output signal from the oscillator was passed through a power amplifier to
produce the necessary current. The key design aspect of the power amplifier was to
generate enough current while producing a clean output signal without large harmonic
distortions. For this purpose, we utilized a simple switch-mode amplifier design whose
design aspects are described below.
VOLTAGE RECTIFIER
A rectifier would be needed to rectify the AC voltage received from the receiver coil
to drive a DC load. A type of circuit that produces an output waveform that
generates an output voltage which is purely DC or has some specified DC
component is a Full Wave Bridge Rectifier. This type of single phase rectifier uses
four individual rectifying diodes connected in a closed loop "bridge" configuration to
produce the desired output. The smoothing capacitor connected to the bridge circuit
converts the full-wave rippled output of the rectifier into a smooth DC output
voltage
CONCLUSION AND FUTURE WORK
At the end of the research, we were able to design a system for transmitting watts of
power wirelessly from the transmitting coil to the receiving coil that was enough to light
a 40W bulb. We were able to design discrete components such as the relaxation
oscillator, switch mode-power amplifier and a full bridge voltage rectifier for the system
design process. We also managed to demonstrate evanescent waves by measuring
exponential decay of voltage as an increase in distance between the transmitter and the
receiver coils.
There can be significant research work that can be done in the future of this research.
Future work includes connecting the relaxation oscillator with the power amplifier using
current amplifier chip for providing enough current to drive the gate of the Mosfet to
drive the efficient class D H-Bridge power amplifier. Also, reduction in the size of the
transmitting and receiving coils and utilizing the regulated signal to power a DC load
could be something that could be worked in the future as a means to make this system
feasible for practical applications.