Description
ABSTRACT
As power requirements for portable devices increase, consumers are looking for easy-to-use charging solutions that can be deployed in a wide array of environments such as home, office, automobiles, airports, schools and more. Wireless charging uses an electromagnetic field to transfer energy between two objects. This is usually done with a charging station. Energy is sent through an inductive coupling to an electrical device, which can then use that energy to charge batteries or run the device. The aim of this work is to design a device that can charge cellphone wirelessly.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background of the project
Increasing reliance on mobile devices such as smartphones, tablets and smart devices has led to an increased demand for efficient and convenient charging solutions. Conventional charging systems, while effective, have limitations such as requiring physical connection, restricting mobility, and damaging the cable. To solve these problems, wireless charging technology, which provides freedom of power transfer without energy, has emerged as a promising solution. One of the wireless charging technologies is inductive coupling, which uses electromagnetic fields to transfer power between the charging pad and the mobile device. Inductive coupling is based on the principle of electromagnetic induction, in which alternating current in a transmitting coil induces a direct current in a closed receiver coil.
The method use in charging portable devices such as cellphone wirelessly is known as inductive charging. Inductive charging uses an electromagnetic field to transfer energy between two objects. This is usually done with a charging station. Energy is sent through an inductive coupling to an electrical device, which can then use that energy to charge batteries or run the device [1].
Induction chargers use an induction coil to create an alternating electromagnetic field from within a charging base, and a second induction coil in the portable device takes power from the electromagnetic field and converts it back into electric current to charge the battery. The two induction coils in proximity combine to form an electrical transformer. Greater distances between sender and receiver coils can be achieved when the inductive charging system uses resonant inductive coupling. Recent improvements to this resonant system include using a movable transmission coil (i.e. mounted on an elevating platform or arm) and the use of other materials for the receiver coil made of silver plated copper or sometimes aluminium to minimize weight and decrease resistance due to the skin effect [2].
An alternating current in the transmitter coil generates a magnetic field which induces a voltage in the receiver coil. It is the simplest method of wireless power transfer the power can be transmitted. [2] The efficiency of the power transfer depends on the coupling between the inductors and their quality. [3] The example of inductive coupling is the transformer. In transformers, there is a core which guides and acts as a path for the flux from primary to secondary.
Wireless electricity acts as Coreless transformer (Air-cored). The three sections were designed and constructed in this research. The first section was the charged controller. The second section was the transmitter and the third was the receiver. In order to portable, battery was used as power supply source which supplies the whole system to operate. The battery was charged by two methods: one was from solar and another was from AC source. The operation of charging battery was performed by charged controller circuit. Wireless charging eliminates the cable typically required to charge mobile phones, cordless appliances and so on. With a wireless charger, the battery inside any battery-powered appliance can be charged by simply placing the appliance close to a wireless power transmitter or a designated charging station. Wireless charging is the well-known Faraday’s law of induced voltage, commonly used in motors and transformers. This thesis is about a device to transfer power wirelessly instead of using conventional copper cables and wires. Wireless power charging is becoming more and more common in new gadgets like smarts phones, tablets and laptops.
1.2 Problem statement
The traditional method of charging phones involves much wires, exposes the charger and the user to different types of risks. The invention of wireless charger brought solution to problem seen in the wired mobile charger and introduces the following advantages.
- Protected connections – No corrosion when the electronics are all enclosed, away from water or oxygen in the atmosphere. Less risk of electrical faults such as short circuit due to insulation failure, especially where connections are made or broken frequently.
- Low infection risk – For embedded medical devices, transmission of power via a magnetic field passing through the skin avoids the infection risks associated with wires penetrating the skin.
- Durability – Without the need to constantly plug and unplug the device, there is significantly less wear and tear on the socket of the device and the attaching cable.
- Increased convenience and aesthetic quality – No need for cables
1.3 Aim and objectives of the project
Aim
The aim of this project is to build a wireless power transmission mobile charger circuit using inductive coupling is to charge a low power devices.
Objectives
The objectives of the study are:
- To build the system prototype
- To eliminate the need of constantly plug and unplug the device
- To reduce the risk of electric shock.
1.4 Justification of the study
The invention of the wireless mobile charger will serve as a means of eliminating the use of wired charger thereby eliminating all the disadvantages attached to the wired charger. Wireless Power Transfer system completely reduces existing high- tension power transmission cables, substations and towers between the consumers and generating station. Wireless Power Transfer system completely reduces the cost of the distribution and transmission become less. The cost of the electrical energy to the consumers also reduces. The power could be transmitted to places to which the wired transmission is not possible.
1.5 SIGNIFICANCE OF THE PROJECT
This work will serve as a means of increasing the use of wireless charger and also make them reliable and efficient for large distance respectively.
The study will serve as a means of making an environmental and user friendly as the wires and mechanical connectors and related infrastructure are not required.
This study was carried out to overcome the problem seen in the Wired charging infrastructure such as space required is more, socket are different types, a small substation required.
To the student involved, this study will serve as a means of becoming familiar with inductor winding, oscillating circuit and wireless transmission
To the engineering profession, this study will serve as means of understanding the full knowledge of wireless transmission using inductor.
1.6 Scope and Limitation of project
The scope of this study covers the building of a wireless charger using inductive coupling which is one of the effective ways to transfer power between points without the use of conventional wire system. Wireless power transmission is carried out between two inductive coils (transmitter coil and receiver coil). As the current through an inductor is what generate the electromagnetic field, this is what drove both coils. The frequency required to drive the MOSFET is produced from the oscillating circuit by using pulse width modulation (PWM). The MOSFET serves as the switching device to occur the electromagnetic radiation from the transmitter coil synchronously. The combination of the number of turns and the diameter determined the inductance.
1.6 Structure of the Project
This section will discuss the layout of the report; the chapters are;
Chapter 2 will look at literature review of the study
- Chapter 3 this involve adopting engineering methodology, then implement the methodology of the study
- Chapter 4 this section will discuss test result, all measurement and analysis will be carrying out of the study
- Chapter 5 will state the conclusion, project appraisal, and recommendation.
- CHAPTER TWO
2.0 LITERATURE REVIEW
2.1 Historical background of the study
In 1826 André-Marie Ampère developed Ampère’s circuital law showing that electric current produces a magnetic field. Michael Faraday developed Faraday’s law of induction in 1831, describing the electromagnetic force induced in a conductor by a time-varying magnetic flux. In 1862 James Clerk Maxwell synthesized these and other observations, experiments and equations of electricity, magnetism and optics into a consistent theory, deriving Maxwell’s equations. This set of partial differential equations forms the basis for modern electromagnetics, including the wireless transmission of electrical energy. Maxwell predicted the existence of electromagnetic waves in his 1873 A Treatise on Electricity and Magnetism. In 1884 John Henry Poynting developed equations for the flow of power in an electromagnetic field, Poynting’s theorem and the Poynting vector, which are used in the analysis of wireless energy transfer systems. In 1888 Heinrich Rudolf Hertz discovered radio waves, confirming the prediction of electromagnetic waves by Maxwell [5].
2.2 Concept of inductive (magnetic) coupling
In inductive coupling (electromagnetic induction or inductive power transfer, IPT), power is transferred between coils of wire by a magnetic field. The transmitter and receiver coils together form a transformer (see diagram). An alternating current (AC) through the transmitter coil (L1) creates an oscillating magnetic field (B) by Ampere’s law. The magnetic field passes through the receiving coil (L2), where it induces an alternating EMF (voltage) by Faraday’s law of induction, which creates an AC current in the receiver. The induced alternating current may either drive the load directly, or be rectified to direct current (DC) by a rectifier in the receiver, which drives the load. A few systems, such as electric toothbrush charging stands, work at 50/60 Hz so AC mains current is applied directly to the transmitter coil, but in most systems an electronic oscillator generates a higher frequency AC current which drives the coil, because transmission efficiency improves with frequency [6].
Magnetic inductive coupling is the oldest and most widely used wireless power technology, and virtually the only one so far which is used in commercial products. It is used in inductive charging stands for cordless appliances used in wet environments such as electric toothbrushes and shavers, to reduce the risk of electric shock. Another application area is “transcutaneous” recharging of biomedical prosthetic devices implanted in the human body, such as cardiac pacemakers and insulin pumps, to avoid having wires passing through the skin. It is also used to charge electric vehicles such as cars and to either charge or power transit vehicles like buses and trains [7][8].
However the fastest growing use is wireless charging pads to recharge mobile and handheld wireless devices such as laptop and tablet computers, cellphones, digital media players, and video game controllers.
The power transferred increases with frequency and the mutual inductance M between the coils, which depends on their geometry and the distance Drange between them. A widely-used figure of merit is the coupling coefficient. This dimensionless parameter is equal to the fraction of magnetic flux through L1 that passes through L2. If the two coils are on the same axis and close together so all the magnetic flux from L1 passes through L2, k = 1 and the link efficiency approaches 100%. The greater the separation between the coils, the more of the magnetic field from the first coil misses the second, and the lower k and the link efficiency are, approaching zero at large separations. The link efficiency and power transferred is roughly proportional to k2. In order to achieve high efficiency, the coils must be very close together, a fraction of the coil diameter Dant, usually within centimeters, with the coils’ axes aligned. Wide, flat coil shapes are usually used, to increase coupling. Ferrite “flux confinement” cores can confine the magnetic fields, improving coupling and reducing interference to nearby electronics, but they are heavy and bulky so small wireless devices often use air-core coils [9].
Ordinary inductive coupling can only achieve high efficiency when the coils are very close together, usually adjacent. In most modern inductive systems resonant inductive coupling (described below) is used, in which the efficiency is increased by using resonant circuits. This can achieve high efficiencies at greater distances than nonresonant inductive coupling [9].
2.3 INDUCTOR CONSTRUCTION REVIEW
An inductor usually consists of a coil of conducting material, typically insulated copper wire, wrapped around a core either of plastic or of a ferromagnetic (or ferrimagnetic) material; the latter is called an “iron core” inductor. The high permeability of the ferromagnetic core increases the magnetic field and confines it closely to the inductor, thereby increasing the inductance. Low frequency inductors are constructed like transformers, with cores of electrical steel laminated to prevent eddy currents. ‘Soft’ ferrites are widely used for cores above audio frequencies, since they do not cause the large energy losses at high frequencies that ordinary iron alloys do. Inductors come in many shapes. Most are constructed as enamel coated wire (magnet wire) wrapped around a ferrite bobbin with wire exposed on the outside, while some enclose the wire completely in ferrite and are referred to as “shielded”. Some inductors have an adjustable core, which enables changing of the inductance. Inductors used to block very high frequencies are sometimes made by stringing a ferrite bead on a wire [10].
Small inductors can be etched directly onto a printed circuit board by laying out the trace in a spiral pattern. Some such planar inductors use a planar core.
Small value inductors can also be built on integrated circuits using the same processes that are used to make transistors. Aluminium interconnect is typically used, laid out in a spiral coil pattern. However, the small dimensions limit the inductance, and it is far more common to use a circuit called a “gyrator” that uses a capacitor and active components to behave similarly to an inductor [7].
REVIEW OF RELATED STUDIES
Authors in [5] proposed a work on how to transfer 60 W (a light-bulb) with ~40% efficiency over distances in excess of 2 meters using a system of coupled magnetic resonances or self-resonant coils by exploring nonradiative magnetic resonant induction at megahertz frequencies. For the experimental validation of the power transfer scheme, the authors utilized two identical helical coils. As driving circuit, the authors use a standard Colpitts oscillator whose inductive element consists of a single loop of copper wire; this loop couples inductively to the source coil and drives the entire wireless power transfer apparatus. The authors used a light-bulb as load of the power transfer system. Authors experimentally obtained and demonstrated the efficiency of nonradiative power transfer over distances up to 8 times the radius of the helical coils. The article presents a quantitative model describing the power transfer, which matches the experimental results to within 5%. Authors discuss the practical applicability of this system and suggest strong directions for further study.
[6] proposed a demonstration of power transfer from a single resonant source coil to multiple resonant receivers, focusing upon the resonant frequency splitting issues that arise in multiple receiver applications. The resonant coupling system is modeled with either single or multiple receivers using a relatively simple circuit. The model takes into account mutual coupling between all coils, and does not make approximations usually associated with the coupled mode approach. The analysis made with the model shows that high Q resonant coupling is key to the efficiency of the system, through an implementation where the primary coil is inductively coupled to the power source and the receiving coils are inductively coupled to the loads. The developed work can help to understand the resonant coupling mechanism and to extend it to multiple mobile receivers. Authors point out that the main challenge is to adjust the lumped capacitances at the terminals of the receivers as they move with respect to the source coil and with respect to one another.
In [7] the authors showed an interesting system of magnetically coupled resonators in terms of passive circuit elements and derive system optimization parameters. The authors demonstrated a method for automatically tuning the wireless power system, so that the maximum power transfer efficiency is obtained for nearly any distance and/or orientation as long as the receiver is within the operating range of the transmitter. A circuit model is presented by authors along with a derivation of system concepts, such as frequency splitting, the maximum operating distance (critical coupling), and the behavior of the system as it becomes undercoupled. This theoretical model is validated against measured data. An adaptive frequency tuning technique is demonstrated, which compensates for efficiency variations encountered when the transmitter-to-receiver distance and/or orientation are varied. The method demonstrated in this paper allows a fixed-load receiver to be moved to nearly any position and/or orientation within the range of the transmitter and still achieve a near- constant efficiency of over 70% for a range of 0–70 cm. In addition, the author demonstrated the potential of their coupled resonators system for operating a commercial laptop. The laptop was powered via the system of magnetically coupled resonators. During the laboratory tests, the laptop battery was removed, and the wireless power system was providing all the power needed for normal operation of laptop. They obtained in the tests an input efficiency of 50%.
Authors in [8] proposed designed and fabricated an efficient and compact wireless power transfer system achieving low-power loss using the switched-mode class-E transmitter of high- efficiency via planar inductive coupling using air coils. This wireless power transfer system was able to achieve a desirable power-delivery response across a wide range of load resistances without any control mechanism. The authors studied two types of air cooling systems to increase the efficiency and the power delivery of the wireless power transfer system. The proposed system is capable of 295 W of power delivery at 75.7% efficiency with forced air cooling and of 69 W of power delivery at 74.2% efficiency with air natural convection cooling. The system can be used to provide power wirelessly to various electronic portable devices, industrial appliances, and many other interesting applications. This technology can be applied to rugged electronics to enable the creation of hermetically sealed units and to eliminate the problem of charging port contamination and corrosion. In environments where sparking and arching hazards exist, this technology can be applied to eliminate an electronic device’s external metallic contacts.
Authors in [9] proposed the design considerations for high energy inductive link. An inductive link is a dc-dc converter built around a coupled transformer, after rectification, the voltage regulator ensures a constant output voltage. This paper discusses the major differences between low power and high power inductive links. An inductive link capable of transferring 20 W of power over a distance of 1 cm with an efficiency of 80% is presented. Both the external and the remote coil have diameters of 6 cm and a thickness of 2 mm. This core link drive will be integrated into biomedical, industrial and automotive applications.
Authors in [11] proposed the relationship between maximum efficiency air gap using equivalent circuits is analyzed and equations for the conditions required to achieve maximum efficiency for a given air gap are proposed. The results of these equations match well with the results of electromagnetic field analysis and experiments. The relationship between frequency and the efficiency of wireless power transfer is studied using electromagnetic field analysis by varying the length of the air gap. The method of moments is used in the electromagnetic field analysis.
THEORITICAL REVIEW
According to the energy transfer mechanism [11], WPT can be categorized into two types, namely: Far- field and Near field WPT system [11].
1.1 Far-Field Wireless Power Transfer
Far-field wireless power transfer which is also called electromagnetic radiation WPT[1], adopts electromagnetic waves like radio frequency signals as a medium to deliver energy in a form of radiation. This is then transferred by the electric field of an electromagnetic wave, which is radiative
Far-field WPT includes microwave power transfer (MPT), Laser Power Transfer (LPT), and Solar Power Transfer (SPT) [11].
Microwave Power Transfer (MPT) Microwave Power Transfer (MPT), which is based on electromagnetic radiation, utilizes the far-field radiation effect of the electromagnetic field to transfer power in free space [12]. A high power transmission level is ensured using this technology when initialized at the base stations and fed to the mobile devices and receiving station. For this to be effective, two points must fall within the line of sight. With the aid of Magnetron, the technology, when deployed with geosynchronous transmission and reception satellites, boosts the power of objects obtained from the base station.
MPT is effective in the area of energy conversion; however, the difficulty experienced in trying to focus the beam over a small area presents challenges [13]. Power transmission begins with the conversion of electrical energy to microwaves, which is then captured by the rectenna. In using this technology, Alternating Current (AC) is not directly converted to the required microwave energy. Conversion to Direct Current (DC) must first be done and then to microwave utilizing magnetron. The rectenna receives the transmitted waves and efficiently changes the microwaves to electricity in the form of DC, then back to AC [7].
Laser Power Transfer (LPT)
Laser power transfer (LPT) transmits power under visible or near-infrared frequency. It uses highly concentrated laser light aiming at the energy receiver to achieve efficient power delivery over long distances. The receiver of laser powering uses specialized photovoltaic cells to convert the received laser light into electricity [11]. LPT has an advantage of energy concentration. However, laser radiation could be hazardous and it requires Line of Sight (LOS) link as well as accurate pointing towards the receiver which could be challenging to achieve in practice. It also requires complicated tracking mechanisms and a large spectrum of devices. Compared to microwave WPT, laser beaming is more vulnerable to atmospheric absorption and scattering by clouds, fog, and rain, which greatly hinders its practical applications [15]. A strong laser beam constitutes serious health hazards to humans and this method is quite expensive to actualize [4].
Solar Powered Satellite (SPS)
It is the largest application of WPT and it makes use of satellites with giant solar arrays and placing them in Geosynchronous Earth Orbit. These satellites play a pivotal role in generating and transmitting power as microwaves to the earth [3].
Near Field Wireless Power Transfer
Near field WPT which is also known as non-radiative wireless charging is based on the coupling of the magnetic field between two coils within the distance of the dimension of the coil for energy transmission [4]. As the magnetic field of an electromagnetic wave attenuates much faster than the electric field, the power transfer over a distance is largely limited. As a result of its safety merits, everyday home appliances as trivial as toothbrushes to more sophisticated machines like electric vehicles have been designed using non-radiative wireless charging. The Nearfield WPT can be classified into two groups namely: Inductive Power Transfer (IPT) and Capacitive Power Transfer (CPT). The inductive power transfer can further be divided into Inductive Coupled Wireless Power Transfer (ICWPT) and Magnetically Coupled Resonance Wireless Power Transfer (MCR WPT) [15]. Although the aforementioned methods vary in transferred distance, efficiency, frequency, transferred power, and resonator dimensions, they all work to achieve wireless power transfer needed for charging.
Inductive Coupled Wireless Power Transfer
The Inductive coupled WPT is the most used method for wirelessly charging low powered devices so far [13]. It transfers power from one coil to another and has been used for powering RFID tags, medical implants [13], in the fields of sensors, wirelessly charging electronic devices and in the car manufacturing industry. The operating frequency of inductive coupling is in the kilohertz range and is typically used within a few millimeters to a few centimeters (20 cm) from the targeted load and its power varies between watt and kilowatt based on transmission efficiency [13].
The advantages of the inductive coupling WPT system include ease of implementation, convenient operation. It is non-radiative and due to its low transmission frequency, it is considered safe for humans. It has a high transfer efficiency of up to 95% at short distances, it eliminates sparks and other hazards in situations like coal mining and there is no danger of either electrocution or short circuit under any power range condition as a result of the coupling being magnetic. However, a limitation of standard inductive charging is that it performs well in considerably short distances of communication, increasing the communication distance adversely drops the performance [16].
1.1.1 Magnetically Coupled Resonance Wireless Power Transfer (MCR WPT)
Magnetically coupled resonance wireless power transfer (MCR-WPT) follows the same basic principles as Inductive coupled wireless power transfer. It also transmits power from a source to a load [16]. However, this magnetically coupled resonant makes use of magnetic resonant coils, which operate at the same resonance frequency. By using magnetically coupled resonant over standard inductive coupling, it is possible to achieve up to fifty percent efficiency for power transmission over longer distances without uttering coil size and power consumption. MCR-WPT technology has attracted significant attention from academia and industries because it can cover all aspects of human life from consumer and medical electronics, smart homes to electric vehicles, showing great potential for further application.
The operating frequency ranges from a few hundred kHz and tens of MHz. MCR WPT has advantages of long-distance within several meters, unaffected by weather environments, line of sight (LOS) is not required when devices are charged, compared to Inductive coupled wireless power transfer, Magnetically Coupled Resonance Wireless Power Transfer has higher transfer power and efficiency and is considered to be one of the most potent techniques for mid-range WPT applications at present. The non-radiative nature of the Coupled magnetic resonant system presents no threat to the environment when compared with the microwave and laser WPT. However, MCR WPT experiences a decrease in efficiency as a result of the axial mismatch between the receiver and transmitter coils, decreased efficiency with increased distance, and complex implementation [16].
Capacitive Power Transfer (CPT). Capacitive Power Transfer (CPT) involves the transmission of energy between electrodes such as metal plates. A charged retaining capacitor is formed by receiver and transmitter electrodes. The transmitter creates an alternating voltage on the transmitting plate, from which the oscillating electric field via electrostatic induction induces on the receiver plate, an alternating potential, which turns into alternating current flow in the load circuit. Though capacitive power transfer is cheaper than Inductive coupling and magnetically coupled resonant, however, CPT requires close contact between the two metal surfaces. Hence, it is greatly limited by range requirements (Arai, 2018). The major drawback with capacitive WPT systems is that electric fields do not share the safety characteristics of magnetic fields, since their relative field strength is much greater, posing a hazard to both humans and electronic devices [10]
Also, the achievable amount of coupling capacitance is dependent on the available area of the device. However, it is difficult to create sufficient power density required for charging when considering normal-sized portable electronic devices which indeed poses a design challenge [10].
