FUTA Journal of Research in Sciences, 2013 (2): 241-248
WITRICITY: A PARADIGM SHIFT IN ELECTRIC POWER TRANSMISSION O.O.E. Ajibola, G.U. Benson and K. Nwosu Department of Systems Engineering, Faculty of Engineering University of Lagos, Akoka, Yaba, Lagos, Nigeria Corresponding author:
[email protected];
[email protected] ABSTRACT This paper presents the concept of power transmission from one point to another without using interconnecting wires. This is achieved through the use of electromagnetic induction and resonant magnetic coupling mechanisms which serve the dual purpose of reducing transmission and distribution losses exacerbated by metallic cabling. In this work, a prototype circuit that uses a 12V battery as its source to drive low power devices through wireless medium over 0.3m radius was built. This nearfield transmission is optimized by transmitting and receiving the electromagnetic waves at a regulated kilohertz of resonance frequency. Ways of improving the efficiency of this wireless electric power transmission, with a view to enhancing the technology so as to replace the conventional use of electric cables was also presented. Keywords: power transmission, interconnecting wire, electromagnetic induction, resonant magnetic coupling mechanism, metallic cabling, near-field transmission.
to optimize the efficiency of such energy systems (Vázquez-Leal et al., 2011). Nevertheless, some of the major issues associated with this electrical grid system of power distribution are the losses which occur during the transmission and the high cost of maintenance, (Sambo, 2008). According to the Change Nigeria Project (2010), Nigeria’s electricity grid has one of the highest transmission and distribution losses in the world with a loss of about 25%. The main reason for power loss during transmission and distribution is the resistance of the wires used for the grid thus making it less efficient. This problem can be solved by choosing an alternative option for power transmission which provides a combination of higher efficiency and lower transmission cost. Wireless Power Transmission (WPT) is therefore one of the promising technologies in this respect and it is the needed alternative for efficient power transmission. WPT can be defined as the transmission of electrical energy from one object to another without the use of interconnecting wires (Vázquez-Leal et al., 2011). It dates back to 1914 when Nikola Tesla, a scientist and the inventor of radio, thought that since it was
INTRODUCTION The basic law of thermodynamics, also known as the law of conservation of energy states that energy can neither be created nor destroyed but can only be transformed (Halliday et al., 2004). The law implies that any system that receives energy can also be made to give out energy. Nature, as we know it, is a vast pool of energy which manifests itself in such different forms as sunlight, heat, wind, etc (Henry, 1960). Since the origin of the human race, man has been learning to use nature’s energy to his benefit. For instance, when fire was discovered by man, the optimum usage of the invention became paramount to him that he transferred the technology to his shelter; where he could use it more directly. Later on, man learned to gather and transport fuels like mineral coal which was then transformed into heat or light. In fact, energy transportation became so important for developing communities that when the electrical energy was invented, one of the biggest and most sophisticated energy networks, the electrical grid, was built. Such distribution grid undoubtedly pushed great advances in science and technology; and further facilitated research activities 241
O.O.E. Ajibola et al., FUTA J. Res. Sci., Vol 9, No. 2, Oct (2013) pp 241-248
possible to transfer information using an electromagnetic field; it would also be possible to transfer electric power using the same transmission medium. Tesla’s experiments were designed to power electric lamps several kilometres away, wirelessly (Vázquez-Leal et al., 2011). Tesla’s findings led him to design the Wardenclyffe Tower, shown in figure 1, as a giant mushroom-shaped wireless power transmitter, with the ultimate aim of transmitting power to all parts of the world. Although due to the dangerous nature of the experiments, low efficiency on power transfer at the time and the depletion of financial resources, Tesla abandoned the experiment.
but a few. According to Ajibola et al., (2012), energy is a crucial element in industrialization and socio-economic development process of any nation. In particular, energy transfer is often realized by using electromagnetic power which can either be transmitted along a guiding medium (that is, transmission lines) or without such supporting medium through WPT systems (Kurs, 2007). Exploitation of WPT dated back to more than hundred years ago when Nikola Tesla proposed the WPT concept. As more sophisticated portable electronic devices are developed the need for WPT technology grew significantly. The basic principle upon which WPT was based depends on magnetically coupled resonance involving two selfresonators; namely the transmitter coil and the receiver coil that have the same resonant frequency transferring energy efficiently over midrange distances. WPT has certain advantages which include efficient midrange power transfer, nonradiative and nearly omnidirectional transmission coupled with cheap cost of installation and maintenance. These properties explain the improved performance of current wireless power transfer systems utilized in various wireless power transfer applications such as electric vehicles, consumer electronics, smart mobile devices, biomedical implants, robots etc. Figure 2 is a typical schematic of WPT system. MATERIALS AND METHODS To enable efficient wireless transfer of power, the method adopted in this work is known as Magnetic Inductive Coupling. This is a resonant coupling that takes place between coils of two inductor-capacitor (LC) circuits having the same resonant frequency; transfer of energy from one coil to the other ensures maximum flux linkage between the coils and enables the system to operate at lower frequencies posing less danger to humans (Karalis et al., 2008). The drawback of WPT method, however, is that, its efficiency reduces as the gap between the two coils is widened; it is therefore good for midrange transmissions of about half a metre apart. Figure 3 is the block diagram representing a typical WPT system.
Figure 1: The 57m Wardenclyffe Tower (Tesla Tower) However, with advances in technology, wireless power transfer using the phenomenon of electromagnetic resonance has become a viable option, at least for short-range distances, since it has high efficiency for power transfer. With energy crises looming as the world approaches the year 2050, energy production, distribution and conservation must be tackled with all vigour (Ajibola and Suley, 2012). Efficient energy transfer methods have always been essential to the future of world energy systems development since they infringe on economic resources, affect the quality of power supply and distort environmental conservation (e.g. through pollution), to name just
242
O.O.E. Ajibola et al., FUTA J. Res. Sci., Vol 9, No. 2, Oct (2013) pp 241-248
Figure 2: Typical diagram of wireless power transfer system
Figure 3: Block diagram showing a typical WPT system
Figure 4: Schematic of Wireless Transmission Model
243
O.O.E. Ajibola et al., FUTA J. Res. Sci., Vol 9, No. 2, Oct (2013) pp 241-248
Figure 5: The transmitter circuit Figure 5 is a 45kHz oscillator circuit that receives 12V to energize the transmitter coil, broadcasting electric power to the receiver circuit, while Figure 6 is the receiver circuit that rectifies the power signal from the transmitter circuit to power low-current loads.
Figure 6: The receiver circuit
The WPT system consists of two main parts: the transmitter circuit and the receiver circuit. The transmitter circuit consists of a 12V battery as power source connected to an oscillator which acts as a signal generator to produce the required frequency of operation which is feed into a power amplifier to increase the power delivered to the transmitter coil which then transfers energy by induction to the receiver circuit. The receiver circuit comprises of the receiver coil where energy is induced in the form of alternating current (AC) and electromotive force (emf) which is boosted and/or rectified to power a DC load. The inductance and capacitance values for the transmitter circuit and the receiver circuits are matched so that they operate at resonant frequency, in order that maximum inductance coupling could exist between the two circuits. This is necessitated
by the fact that if two resonant circuits are tuned to the same frequency within a fraction of their wavelength, standing waves will be developed between the inductors, which will enable electricity to be transferred from one object to the other more efficiently. Since the resulting resonant wavelength is much larger than that of the resonators, the field can circumvent extraneous objects in the vicinity and thus, the mid-range energy transfer scheme will not require line-of-sight. The schematic for a typical WPT model is as shown in figure 4.The circuit diagrams adapted in our experiment is as shown in the figures 5 and 6. The materials used for this research work includes: 12V battery, Ceramic and Electrolytic Capacitors (60pF, 33pF, 100nF, and 10nF), Resistors and Potentiometer, MOSFETs or Transistors, 555 IC or 244
O.O.E. Ajibola et al., FUTA J. Res. Sci., Vol 9, No. 2, Oct (2013) pp 241-248
7555 IC, Diodes (1N4001), 23 Specific Weight Gravity (SWG) wires for coils, LED Bulbs and 5V Bulbs and connecting wires. The materials are
arranged as shown in figure 2. Figures 7 and 8 show the laboratory setup of the experiment.
Figure 7: A view of the experimental setup in the Robotic Laboratory
Figure 8: A view of the experiment showing evidence of wireless transmission of electricity Some of the mathematical equations and governing principles deployed at various stages in the execution of the project work are as follows: Flux linkage and induced EMF (Faraday’s Law of Electromagnetic Induction): (1) Mutual Inductance for each coil: (2) Electromagnetic Inductive Resonance Equations: (3) (4)
245
O.O.E. Ajibola et al., FUTA J. Res. Sci., Vol 9, No. 2, Oct (2013) pp 241-248
Total Induced Electromotive Force due to Magnetic Induction: (5) RESULTS The summary of our results as interpreted in graphical form are as presented in the following Figures:
Figure 9: Graph of variation of output voltage against distance between terminals increases
Figure 10: Graph of efficiency of the device as the distance between the terminals increases
246
O.O.E. Ajibola et al., FUTA J. Res. Sci., Vol 9, No. 2, Oct (2013) pp 241-248
Figure 11: Graph of output voltage with varying frequency significant power may be transmitted over a range of several meters. Unlike the multiple-layer windings typical of non-resonant transformers, such transmitting and receiving coils are usually single layer solenoids or flat spirals with series capacitors, which, in combination, allow the receiving element to be tuned to the transmitter frequency and reduce losses. Moreover, the signals can be made more directional towards the receiver coil by using a conical coil as a transmitter instead of the solenoid coil used in this study. The wireless power system discussed in this paper is proposed for use in devices whose batteries or power source can be completely replaced in the nearest future by wireless power. Such devices include mobile phones, laptops, lamps, alarm clocks, desk lights, remote controls, radios, microwaves, toasters, blenders, and other kitchen and home appliances that are always on or around countertops, desks, or any surface that can be used as an integrated wireless power transmitter, (PCTI, 2012). The system is sustainable, environment friendly, safe and the cost of installation is low. Application of the technology is readily found in powering contactless smartcards. However, one of the drawbacks of the technology is the relatively low efficiency over long range distances of several metres.
DISCUSSION This research presented a comprehensive analysis of the wireless power transfer technology using inductive and resonant coupling techniques. It includes an empirical system designed to analyze circuit performance, investigate optimum coil designs and other circuit components that can be used to practically implement a more efficient wireless power system with minimal wasted power. In this design, each of the coils has an additional transmitting and receiving coil attached to it that are identical to their counterpart, except being only half the size. In theory, the two coils work together to transmit magnetic waves to the boosted receiver, while using the same current that a single coil system would (RamRakhyani et al., 2011). It was also discovered that the diameter of the coils affect the efficiency as well, and was considered during the design of the system. The application of resonance, however, generally improves the efficiency of the systems, by channeling the magnetic field to the receiver coil that is made to resonate at the same frequency as the transmitter. When resonant coupling is used, the two inductors are tuned to a mutual frequency and the input current much more conveniently drives the system, as the circuit becomes purely resistive. In this way, 247
O.O.E. Ajibola et al., FUTA J. Res. Sci., Vol 9, No. 2, Oct (2013) pp 241-248
Halliday, D., Reswick, R. and Walker, J. (2004). Fundamental of Physics, 6th edition. John Wiley and Sons Press Inc., USA. Héctor Vázquez-Leal, A. Gallardo-Del-Angel, R. Castañeda-Sheissa (2011). The Phenomenon of Wireless Energy Transfer: Experiments and Philosophy. InTech Open Access Publisher, Croatia (accessed from http://www.intechopen.com). Henry, T. Moray (1960). The Sea of Energy in which the Earth Floats: The Evolution of Energy and Matter, 4th edition. pp. 19-20 (accessed from http://www.tesla.hu). Karalis, A., Joannopoulos, J. and Soljacic, M. (2008). Efficient wireless non-radiative mid-range energy transfer, Elsevier Annals of Physics (323): 34–48. Kurs, A. (2007). Power transfer through strongly coupled resonances, Massachusetts Institute of Technology, Master of Science in Physics Thesis (accessed from http://www.intechweb.org) PCTI (2012). http://www.pcti.pctiltd.com/download/articals/Wi Tricity.pdf (accessed: June 14, 2012) RamRakhyani, A.K, Mirabbasi, S, and Chiao, M (2011). Design and Optimization of ResonanceBased Efficient Wireless Power Delivery Systems for Biomedical Implants, IEEE Transactions on Biomedical Circuits and Systems pp. 13-16.
CONCLUSION This paper presented the report of the study on wireless power transfer as an alternative option for transferring electricity from one place to another. This concept offers greater possibilities for transmitting power with negligible losses and ease of transmission than the conventional wires. Its drawbacks were highlighted, and theoretical considerations for its improvement were also presented. We can therefore expect with certitude that within the next couple of years, wires will be completely done away with and electric power transfer and distribution will be done wirelessly. REFERENCES Ajibola, O.O.E. and Suley, E.O. (2012). Cow Dung – Water Hyacinth Sludge: A Veritable Source of Renewable Energy. Journal of Sustainable Development and Environmental Protection 2(1): 49-58 Ajibola, O.O.E., Ibidapo-Obe, O. and Sofoluwe, A.B. (2012). Developing a viable renewable energy policy: a pathfinder to millennium development goals and vision 20:2020. International Academy of African Business and Development (IAABD) conference is entitled “African Business and Development in a Changing Global Political Economy: Issues, Challenges and Opportunities”. Change Nigeria Project (2010). CNP’s Position on Nigeria’s Energy Sector http://changenigeriaproject.org/index.php?option= com_content&view=article&id=146:exit-offoreign-companies-fromnigeria&catid=87:CNP%20Position&Itemid=104
248
