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INTRODUCTION
1.1 OVERVIEW
To address the challenges related to the expansion of air traffic, to the dramatic increase of jet fuel price, and to environmental concerns, the aeronautics industry is seeking technological and process innovations in aircraft maintenance. In this context, aircraft health monitoring (AHM) is one of the major challenges faced by aircraft manufacturers. Main applications of AHM are the airframe, the main engines, and the main systems (such as Auxiliary Power Unit—APU), all major contributors to Aircraft “Delay and Cancellation”.
One of the major issues is the prediction of failures to prevent structure or system damages by anticipating the maintenance action necessary to avoid “events.” Such predictive service is especially relevant for the structural health monitoring (SHM).
SHM therefore consists mainly in the monitoring of corrosion, of cracks and of impact damages taking place during the aircraft life. It is generally considered as a powerful tool to decrease inspection costs, to optimize margins in mechanical design, and consequently, to reduce aircraft weight, fuel consumption and emissions of greenhouse gases.
1.2 ENERGY HARVESTING
Energy harvesting (also known as power harvesting or energy scavenging) is the process by which energy is derived from external sources (e.g. solar power, wind energy, thermal energy, salinity gradients, and kinetic energy) captured and stored for small wireless autonomous devices, and wireless sensor network.
Energy harvesters provide a very small amount power for low- energy electronics. While the input fuel to some large scale generation costs resources (oil, coal, etc.) the energy harvesters is present ambient background and is free. For example, temperature gradients exist from the operation of a combustion engine and in urban areas; there is a large amount of electromagnetic energy in the environment because of radio and television broadcasting.
1.3 TYPES OF ENERGY HARVESTING:
1.3.1 Photonic
Common photonic harvesters rely on solar energy drawn with the use of photovoltaics. Photovoltaic convert sunlight into electricity, and are commonly made from semiconductors. They may be solar cells or panels. A tiny, inexpensive solar cell can generate 150 watts of energy at noontime, so they can be relatively powerful and plentiful sources of energy.
The most obvious drawback of photonic harvesting is that sunlight is not on 24 hours a day, which affects the amount of voltage generated. Voltage is also affected by waning light from dusk or creeping light from the dawn, both of while change the angle of incidence of the light which hits the device. Susceptibility to pollutants such as dust that blocks light from the cells may further impede their efficiency. The fragility of photovoltaic devices is still yet another concern.
1.3.2 Thermal
Unless objects are at absolute zero, they have thermal activity. Differences in temperature between objects produce thermal gradients that can be used to generate electricity nearly everywhere on Earth. Of course it is not feasible or practical to use any object in existence to do this, as factors such as durability, cost, and efficiency would need to be factored in.
Thermoelectric devices used for energy harvesting convert thermal activity into electricity are constructed from semiconductors. They don't require generators or pumps or fluids, and don't require copius amounts of materials to build. The main requirements for operation are a heat source and a heat sink.
Because thermoelectric elements produce DC power, a further requirement is that of a DC-DC converter to ensure stability of the potential produced by the power source. One of their drawbacks is that they are not as efficient as striling engines.
1.3.3 Vibrational
Vibrational devices feed off motion produced as a by-product in order to generate power, and so are natural AC power sources. Because they are AC, they require rectifying and regulatory circuits. Sources include the human gait, trains, motors, engines, and radio frequencies.
Piezoelectric materials produce pressure changes brought about by sound waves or touch or mechanical strain. Crystals made from this substance form diaphragms or are linked to them, and they can function as speakers or microphones. For energy harvesting, piezoelectric generators are usually cantilevers with masses attached to a free end.
Vibrational harvesting devices are useful monitoring equipment and machinery in industrial environments without the use of batteries or cables. However, this method is not good to use in devices where mobility is a requirement, due to concerns with stability and interference that will impact features such as velocity and noise. They are also best used where the input is at a consistent, predictable frequency.
ABSTRACT
We suggest an innovative architecture for an efficient energy generator devoted to the powering of a wireless sensor net- work deployed for aircraft health monitoring. This battery-free generator captures energy from its environment (transient thermal gradients as a main source, and vibrations as a secondary source allowing early biasing of the generator) and stores this energy in ultra capacitors. In this way, this multisource architecture benefits from the synergy between energy scavenging and harvesting: vibrations bring low but early and permanent energy. They also contribute to energy harvesting during cruise while thermal gradients have vanished. The uses of active diodes and of a very low bias current of 10 nA/branch allow achieving ultralow power consumption, experimentally demonstrated on two different CMOS technologies. It is also proven that enough energy could be delivered to power the functions of a wireless sensor node.
D. Meekhun, V.Boitier suggested that Primary batteries can be eliminated through the use of environmental energy capture technique, which use an energy conversion transducer tied to an integrated rechargeable power storage device, then enabling the wireless sensor node an almost infinite lifetime. In the aeronautics application context, the use of secondary (rechargeable) batteries is prohibited, as they suffer from even worse environmental limitations than primary ones.
G. D. Szarka, B. H. Stark, and S. G. Burrow, suggested that the maximizing the transfer of energy from the transducer to the storage devices. Second, as the voltage on the UC storage devices will vary according to their discharge, a voltage regulation is needed. It should be given to conversion efficiency. For both of these design challenges, another important requirement is micro scale compatibility thus prohibiting the use of bulky passive devices as the ones needed for some impedance matching strategies and harvested energy being limited, the quiescent power consumption of the energy generator should be as low as possible. This is required for two reasons: the first one is that many SHM scenarios are using duty cycles with much longer periods in quiescent mode than in the active one and the second is related to the self-discharge current of UCs which is in the order of μA. The quiescent current of the power converter should not be higher than this value or even be made negligible compared to it. A tradeoff will then have to be made between efficiency and power consumption.
Atmel Germany Gmbh, Heilbronn, suggested that this multisource and battery-free energy harvesting architecture was validated on two technologies: a high-voltage 0.35-μm CMOS technology from AMS available via the French Multi- project Chip (CMP) service and a smart power 0.8-μm Bipolar CMOS DMOS merged technology on SOI (TFSMART1) pro- vided by Telefunken Semiconductors.
D. Samson, M. Kluge, T. Becker, and U. Schmid, Suggested that an ultralow power converter for a multisource battery-free energy generator dedicated to aeronautics applications that would enable almost infinite energy- autonomy to a WSN node. It provides a regulated voltage with a very low quiescent current consumption (300 nA). The pro- posed architecture is based on two energy sources and on ultra- capacitors (UCs) for storage.
M. E. Kiziroglou, S. W. Wright, suggested that it delivers an alternating output which spectrum exhibits fundamental frequency around 60 Hz, at the rotating speed of the engine inlet fan. These vibrations originating from aircraft engines are not intense enough to power all the functions of the WSN node.
C. Rossi and P. Aguirre suggested that if the value of the UC is too small, it will be rapidly charged but its maximum operating voltage, together with its small value, will limit the stored energy. On the contrary, if its value is too large, the time constant will prevent collecting the maximum of energy since the UC will not have the time to reach the voltage saturation. To optimize this tradeoff, we simulated the charge of an UC via an ideal diode during the aircraft take-off and compared the open-circuit voltage to the one of a matched load. In our case, given the fact we use two UCs in series; the optimized value of each one is 1 F.
PROPOSED WORK
In this paper, we present an ultralow power converter for a multisource free energy generator dedicated to aeronautics applications that would enable almost infinite energy autonomy to a WSN (wireless sensor network) node. This free energy generator captures energy from its environment (transient thermal gradients as a main source, and vibrations as a secondary source) allowing early biasing of the generator.
An advantage of a TEG compared to a vibration-based energy harvester is that it has no moving parts. Disadvantages are that TEGs are relatively inefficient when low thermal gradients are present and that until recently the dimensions and weights of the devices were too large to integrate them with MEMS technologies. Because aircrafts flying at high altitudes are subject to large thermal gradients, the use of TEGs to power wireless SHM sensors for aerospace applications is a field of interest.
The prototype device, which is still being optimized and is only available for testing and evaluation, is proposed as potential power supply for wireless sensor network applications where waste heat is available.
BLOCK DIAGRAM DESCRIPTION
The proposed system is used to generate the power from heat, vibrational energy using Peltier and Piezoelectric device. These two renewable sources are stored into the super capacitor. The stored energy is given to the input of the boost converter. The Boost converter will step-up the output Voltage than the input voltage. The Boost converter output Voltage is given to the rechargeable battery for charging purpose. The battery output is given to the inverter and then the inverter will convert DC voltage into AC voltage. The Converted AC voltage is given to the high voltage load.
System Requirement:
Software Requirement:
Language : Embedded ‘C’
Compiler : PIC C Compiler, PIC Downloader.
Hardware Requirement:
• Controller & supporting components (PIC16F877A).
• Boost Converter Circuit
• Power Sensing Circuit
• Peltier -1
• Super capacitor – 1
• 6V Battery – 1
• Inverter - 1
THERMO ELECTRIC ENERGY:
TEG is an acronym for ‘thermoelectric generator’. A TEG is a device utilizing one or more thermoelectric models as the primary component/s, followed by a cooling system that can be either passive or active. Such as an open air heat sink, fan cooled heat sink, or fluid cooled. These components are then fabricated into an assembly to function as one unit called a TEG. When heat is applied to the hot side of a TEG, electricity is produced. Almost any heat source can be used to generate electricity, such as solar heat, geothermal heat, even body heat! In addition the efficiency of any device or machine that generates heat as a by-product can be drastically improved by recovering the energy lost as heat.