The need of energy increases in industrial advancement. To meet the high energy demands with limited natural resources it is desirable to develop energy harvesting systems. This thesis deals with the design of a similar energy efficient system for sensors in production machines. The basic motivation of the system application is to avoid the use of batteries. The batteries need to be replaced after a period of time whereas an energy harvesting system produces its own electrical energy by converting available forms of energies into useful electrical energy for example solar, thermal or vibration energy of the machines into useful electrical energy.
Index
1 Introduction
2 Energy harvesting
2.1 Thermoelectric energy harvesting
2.2 Solar energy harvesting
2.3 Radiofrequency energy
2.4 Vibration energy
2.4.1 Variable capacitance systems
2.4.2 Piezoelectric Material Systems
2.4.3 Magnetostrictive energy harvesting
2.4.4 Electromagnetic induction
3 Magnetic induction system design
3.1 Laws of electromagnetic induction
3.1.1 Geometry
3.1.2 Magnetic flux generated by the bar magnet
3.1.3 Coil inductance and resistance
3.1.4 Parameters of magnetic material and magnets
4 Energy harvesting system design
4.1 Vibration analysis
4.2 Friction force
4.3 Electromagnetic damping force
4.4 Voltage and power generation
4.5 Coil- through- magnet induction
4.6 Magnet- through- coil induction
5 Simulations
5.1 Resistance of wire against turns of coil
5.2 Damping against turns of coil
5.3 Amplitude of vibration against turns of coil and magnetic field
5.4 Damping force against turns of coil and magnetic field density
5.5 Voltage against turns of coil and magnetic field density
5.6 Amplitude against turns of coil and the air gap
5.7 Damping force against turns of the coil and the air gap
5.8 Voltage against turns of coil and the air gap
5.9 Power against turns of coil and the air gap
6 Adjustable energy harvesting system
6.1 Active systems
References
Abstract
Thema der Arbeit: Energy harvesting with the help of electromagnetic induction
Erstellt von: Usman Butt
Kenn-Nr.: 08 - M 3191 / 4-Be
Abgabedatum: 16.02.2009
The surrounding energy in Production machines is present in form of vibrations. In this Thesis an Energy harvesting system will be developed which is able to convert these vibrations into useful electrical energy. The principle of electromagnetic induction shall be used whereas the focus should be set on a self-adjusting resonance system.
After a Literature Research a mechanical model of an energy harvesting system must be developed and possibilities of a self adjusting resonance system must be shown. Additionally the mechanical and electrical components of the system will be described mathematically. This description should include the influencing parameters of the system.
Furthermore, the system must be optimized for a maximum energy output. By means of simulation (e.g. with Matlab / Simulink) must be accomplished with the help of an already developed mathematical model. The goal of this simulation is an optimized energy harvesting system. The possibilities of a self adjusting resonance system must be explored to run the system for an optimized energy output.
Figure Index
Figure 1: Variable capacitance systems
Figure 2: Piezoelectric energy harvesting
Figure 3: Electromagnetic induction
Figure 4: applications of vibration energy with electromagnetic induction
Figure 5: Electromagnetic induction
Figure 6: Schematic diagram of magnet and coil
Figure 7: magnetic flux on a single wire turn
Figure 8: Block diagram of energy harvesting model
Figure 9: voltage-current and power-resistance relations
Figure 10: different types of wire winding
Figure 11: Nomogram
Figure 12: Hysterisis diagram
Figure 13: Model of energy harvesting system
Figure 14: Frequency response diagram with different values of D
Figure 15: Static and sliding friction between guidance and the magnet
Figure 16: Contact geometry between guidance and the magnet
Figure 17: Resistance against no of turns
Figure 18: Damping factor against no of turns
Figure 19: Amplitude against coil turns and magnetic field
Figure 20: Damping force against turns N and magnetic field density T
Figure 21: Voltage against no of turns and magnetic field
Figure 22: Power against no of turns and magnetic field
Figure 23: amplitude against N and the gap between coil and the magnet
Figure 24: Damping force against the air gap and coil turns N
Figure 25: voltage against coil turns and air gap
Figure 26: Power against coil turns and air gap
Figure 27: amplitude against number of turns of coil and frequency
Figure 28: voltage against number of turns of coil and frequency
Figure 29: Power against number of turns of coil
1 Introduction
The need of energy increases in industrial advancement. To meet the high energy demands with limited natural resources it is desirable to develop energy harvesting systems. This thesis deals with the design of a similar energy efficient system for sensors in production machines. The basic motivation of the system application is to avoid the use of batteries. The batteries need to be replaced after a period of time whereas an energy harvesting system produces its own electrical energy by converting available forms of energies into useful electrical energy for example solar, thermal or vibration energy of the machines into useful electrical energy.
A lot of research has already been done to construct small generators using different techniques to avoid the use of batteries for the inbuilt sensors in production machines. These generators use different techniques to convert the different forms of energy into electrical energy. Solar cells, thermopiles, piezoelectric materials and electromagnetic induction are most commonly used methods for this transformation of energy. Each method has its own limitations. The aim of this Master thesis is to develop an energy harvesting system using the principle of electromagnetic induction to supply sensors with electrical current in production machines. Each method of energy conversion is shortly discussed in the first chapter to compare the potential of all these methods. The most suitable method for an application in the environment of production machines is selected. After comparison, electromagnetic induction is found as the most promising way of energy harvesting for sensors in production machines. Later on two different ways of electromagnetic induction magnet through coil induction and coil through magnet induction are discussed and explained. Using these methods of electromagnetic induction in a simple system, a model of an energy harvesting system is described and simulations are performed with the help of Matlab to extract the maximum possible energy using these principles. The output voltage and power is calculated using laws of electromagnetic induction for different parameters e.g. number of turns of coil and magnetic field intensity of the magnet. Output power is also calculated for different frequencies when the forcing frequency is varied over the time. To ensure the maximum power output, the system must operate at resonant frequency i.e. the forcing frequency is equal to the natural frequency of the system. The natural frequency can be changed manually by replacing the spring with a different spring constant or changing the hanging mass.
2 Energy harvesting
Energy exists in different forms in the environment. The goal of this thesis is to develop an energy harvesting model for sensors in production machines, so the possibilities of using available energy in the environment of a production machine has to be discussed. Energy around a production machine can be found in form of solar energy from the sunlight and tube lights, thermal energy from heating of motors and other moving elements, electromagnetic waves energy from the radio waves or vibration energy from the kinetic energy of the oscillating parts of machines. Different methods of harvesting energy from all these forms are described in the next section.
2.1 Thermoelectric energy harvesting
Thermal gradients in the enviroment are directly converted to electrical energy through the Seebek or thermoelectric effect. The offset temperature between opposite segments of a conducting material results in heat flow and consequently charge flow. Thermopiles consists of n- and p-type materials which are electrically jointed a high temperature junctions are therefore constructed, allowing heat flow to carry the dominant charge carriers of each materials to the low temperature end, establishing in the process a voltage difference across the base electrodes.
Thermoelectric energy harvesters find their application in remote wireless sensors and wrist watches, as heat energy from the human body is radiated through the watch into the environment. A micro-thermoelectric harvester capable of producing 15 microwatt/cm² from a 10° C temperature gradient was demonstrated by Stordeur and Stark [STO97]]. The device provided relatively high output voltages of 100mV/°C. A MEMS thermoelectric harvester was also reported to offer 1.5 microwatt from 10°C temperature differential [GLO99}]. Applied Digital Solutions Co. released product that could generate 40 microwatt of power from a 5°C temperature differential using 0.5 cm² area with a thickness of few millimeters. The output voltage was about 1 V [PES02]. Another product could output 2.5 W power with 3 V in 8.4 cm² area cells from 200 °C offset temperature [HIZ05].
In brief, the generated voltage and power is proportional to the temperature differential and the Seebeck coefficient of the thermoelectric material. Large thermal gradients are necessary to produce practical voltage and power level. Nevertheless, temperature differences greater than 10°C are rare in a micro-system, consequently producing low voltage and power level.
2.2 Solar energy harvesting
Solar or other light energies can be converted into electrical power by using solar cells, which are commercially produced and well characterized. The magnitude of energy generated varies from ~15 microwatt/cm² in noon-time sunlight to 10 microwatt/cm² indoor, incandescent lighting [BUL05]. The output energy depends on the material used. For example, crystalline materials such as silicon and gallium arsenide have moderated absorption efficiency and high conversion efficiency about 15% ~ 30% while conversion efficiency (< 10%). The choice of materials also relies on its spectral response and the light source of interest.
A thin film solar cell to power electrostatic actuators MEMS was developed in [LEE95]. The array contained 100 single cells connected in series with a total area of only 1 cm². Under incandescent situations, an area of 1 cm² produced around 60 microwatt of power [VAN25]. A prototype solar powered hearing aid was integrated into a pair of glasses. The current variation due to light intensity was overcome by a power converter integrated circuit.
In circuit design, the standard solar cell can be modeled as a voltage source in series with an internal resistor. A single solar cell has an open circuit voltage of ~ 0,6 V, but panels with series and parallel combinations of such cells can generate any required voltage for the circuit. Although the output voltage is nearly constant in rated range, the current varies with light intensity. Solar power is still more expensive than conventional methods.
2.3 Radiofrequency energy
Another potential way of powering wireless sensors is wireless energy transmission via electromagnetic waves for radiofrequency radiation. This concept utilizes two different RF energy sources: ambient and controlled RF sources. It has been shown that electronics could efficiently capture ambient radiation and convert them to useful electricity. Harrist tried to charge a cellular phone battery by collecting ambient 915 MHz RF energy [HAR04]. Although the battery could not be fully charged, he observed 4 mV/s charging rate. Only electronics with ultra-low power consumption may be driven by this approach, but the amount of harvested power is extremely low, typically in the range of a few μW.
One approach of controlled RF sources is based on RF link which consists of primary and secondary coils. When two coils are close to each other, the input AC power can be wirelessly transferred from primary coil to secondary coil via the inductive link. Yi [YIH04] used RF link to drive a wireless temperature sensor for bearing monitoring. Power of 10 mW could be transferred over a distance of 1 ~ 2 cm at a frequency of 8.7 MHz and the diameters of two coils were 7 cm and 6 cm respectively. VanSchuylenbergh and Puers [VAN01] transferred 20 mW power for driving a strain sensor with transmission distance of 3 ~ 7 cm at 1MHz RF. Vandevoorde and Puers demonstrated an inductive link with capability of transferring 20 W power over a distance of 1cm. The major advantages include simple configuration, mature electronics, and adjustable transferred voltage on the secondary coil. But it has several limitations such as short transmission distance <5 cm; variation of coupling efficiency on coil alignment, and bulky dimension due to two coils.
Another controlled microwave transmission, beamed RF source has the same functionality. A source antenna transmits microwaves through the air to a receiver, which can either be a typical antenna with rectifying circuitry to convert the microwaves to DC power or a rectenna (rectifying antenna) that integrates the technology to receive and directly convert the microwaves into DC power. With the usage of rectennas, efficiencies in a range of 50%–80% range for DC to DC conversion could be achieved. Significant testing has also been done across long distances and with kW power levels [CHO04]. Briles invented a RF wireless energy delivery system for underground gas or oil recovery pipes [BRI04]. The RF energy was generated on the surface and traveled through the conductive pipe, which worked as an antenna or a waveguide. The sensor module at the bottom of the pipe captured this energy and powered the electrical equipments. With a 100 W transmitted power from the surface, it was estimated that around 48 mW of instant power could be captured after traveling 1.6 km along the pipe. Mascarenas [MAS06] recently experimentally transferred 2.5mW power from X-band source horn antenna with 1W 10GHz radiation to a receiver horn antenna for driving piezo-sensor nodes over a distance of 0.61 m.
2.4 Vibration energy
Vibrations are available in many environments of interests including commercial buildings, highway, aircrafts, trains, industrial facilities and production machines. In general, frequency and acceleration are the key parameters to characterize vibrations. The higher those values, larger will be the power provided to the energy harvesters.
Abbildung in dieser Leseprobe nicht enthalten
Table 1: Comparison of different vibration sources
Vibration energy harvesting techniques are classified into electromagnetic, electrostatic, piezoelectric, and magnetostrictive approaches. The current status of investigations on the energy harvesting techniques is reviewed as below. Four common techniques will be discussed individually in the following section.
2.4.1 Variable capacitance systems
The electrostatic energy harvesting is based on the changing capacitance of vibration-dependant plates, or variable capacitors whose electrodes are moveable to each other and separated by a dielectric to form a capacitor (figure 1 [IMTEK]). By initially placing charge on the electrodes and moving the electrodes apart, mechanical motion can be converted into electrical energy [ROU04]. Energy density of the harvester can be increased by reducing the capacitor spacing. The energy density, however, is also decreased by reducing the electrode surface area. Meninger [MEN76] gave a good explanation of the merits of both charge and voltage constrained conversion. In theory more power could be produced from a voltage constrained system. Furthermore, the electrostatic energy harvesting device attained power density of 0.23 μW/cm3 at a vibration of 2.5 kHz. Roundy optimized the electrostatic harvester and improved the output power density up to 110 μW/cm3 at 120 Hz vibration. The working principle of such a system is shown in Figure 1.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1: Variable capacitance systems
2.4.2 Piezoelectric Material Systems
The piezoelectric-based approach converts the mechanical energy in the form of mechanical strain of the piezomaterial electrical energy by the direct piezoelectric effect (Fig 2 [PIEZO]). It is the most favored of all these vibration-based methods because of reasonable electro-mechanical coupling coefficient, no bulky accessories (such as coil or permanent magnet), and feasibility for MEMS applications.
[ELV01] Elvin excited a 3 Hz bending vibration of a simple beam with a surface-attached PVDF film to generate electrical power and drive a telemetry circuit. A switch was added to the circuit to automatically discharge and charge the storage capacitor, which produced the output voltage range of 0.8~1.1 V for a RF transmitter. [PFE01] Pfeifer applied a similar piezo-bimorph to supply a PIC16C71 microprocessor (rated to 2.5V and <40 μW) and a RFID tag operating 13.56 MHz. The peak power density of this device was 98 μW/cm³ and the peak voltage was on the order of 1.5 V under 1 Hz manual excitation.
To dynamically optimize the power transfer efficiency, an adaptive AC-DC rectifier with an output capacitor, rechargeable battery, and switch-mode DC-DC converter was introduced by Ottman [OTT02]. A power density of 196 mW/cm³ was obtained. However, if the voltage produced by the piezo-harvester was less than 10 V, then power flow into the battery was reduced because of losses in the additional circuit components. [ROU04] Roundy and Wright derived an equivalent electrical-mechanical circuit model to analyze the cantilever type of piezoelectric harvester. The maximum output power through a 300 kΩ resistor reached 375 μW/cm³ subjected to a vibration of 2.5 m/s² at 120 Hz. For further improvement of the output power, Gao and Cui [GAO05] employed the same theoretical model with optimized geometry of the beam. The maximum output power density of a triangular beam could achieve 790 μW/cm³ with a 43.5 kΩ resistor under a vibration of 9m/s2 at 72 Hz; while the maximum output power density from a rectangular beam under the same scenario was 520 μW/cm³
Recently, a new method of piezoelectric vibration energy harvesting called “Synchronized switch harvesting on inductor” (SSHI) was developed [BAD05]. It was developed from a popular method of vibration suppression referred to as “Synchronized switching damping on inductor” (SSDI). It adopted an electrical circuit containing an inductor and an electrical switch to maximize charge flow from a PZT, and could enhance the output power four times. Advantages and disadvantages of piezoelectric materials are listed below.
Abbildung in dieser Leseprobe nicht enthalten
Figure 2: Piezoelectric energy harvesting
2.4.3 Magnetostrictive energy harvesting
MsM (Magnetostrictive material) has been recently considered in applications of vibration energy harvesting. It utilizes the Villari effect, where vibration induced strain of an MsM produces a change in the magnetization of the material. Upon dynamic or cyclic loading, this change in magnetization is converted into electrical energy using a pick-up coil or solenoid surrounding the magnetostrictive layer according to Faraday’s law.
[STA05] Staley and Flatau attempted to apply a Terfenol-D alloy for energy harvesting. The Terfenol-D rod was operated in axial mode rather than flexural bending mode. It had bulky dimension because of 1000-turn pick-up coil and 1500-turn DC actuation coil for generating bias magnetic field. The maximum output power was up to 45 μW at resonant frequency of 45 Hz, and the amplitude of AC output voltage was less than 0.35 V which was unsuitable for voltage rectification. Although new developed giant Galfenol was tested in experiments, the output performance was not significantly enhanced and still unlikely to output any DC voltage.
Due to the giant magnetostriction of Terfenol-D up to 2000μm , Terfenol-D has been used as an instrument to provide large strains in a PZT layer for energy harvesting. A thin PZT (Lead Zirconate Titanate) layer sandwiched by two Terfenol-D layers is placed under time varying magnetic field. Since the outer Terfenol-D layers will induce higher strains than the traditional bending mode in the PZT layer, the PZT layer will generate more charge. The time-varying magnetic field could be induced from ambient vibrations by a permanent magnet attached to either a cantilever beam or a spring. [HUA03] Huang developed a Terfenol-D/PZT/Terfenol-D composite harvester which could achieve 1.2 mW of power at resonant frequency of 30 Hz at acceleration of 5 m/s². They predicted that more than 10 mW could be harvested from a volume of 1 cm3 laminate at 5 m/s2 acceleration. [BAY04] Bayrashev also fabricated a diameter of 0.5 mm thick PZT disc sandwiched between two Terfenol-D discs with thickness of 1.5mm. When the laminate was exposed to low frequency (<100 Hz) varying magnetic field, the output from PZT layer was found to be in a range of 10~80 μW.
Wang and Yuan first proposed the feasibility of using amorphous metallic glass (Metglas 2605SC) harvesting energy from ambient vibrations [WAN06]. They introduced an equivalent electrical-mechanical circuit model to analyze the output performance of the harvester, and optimized the configuration of bias magnets and output performance. The max output power reached 200 μW. Lately they completed the system integration design and enhanced the output performance by utilizing transversely annealing treatment to Metglas.
Compared to piezoelectric based harvesters, Metglas-based harvesters have higher coupling efficiency (>0.9), higher Curie temperature, higher flexibility to be integrated with curved structures, and no depolarization problem. It is suitable to work in harsh and high frequency environments. However, it has relatively large dimension so it si difficult to built MEMS application, because of the pick-up coil and permanent magnets.
2.4.4 Electromagnetic induction
The energy exists practically in every moving part of a production machine in the form of vibration energy. Goal is the conversion of this mechanical energy into electrical energy. An induction system can be used to achieve the goal. The basic principle is shown in the following figure 3.
Abbildung in dieser Leseprobe nicht enthalten
Figure 3: Electromagnetic induction
Abbildung in dieser Leseprobe nicht enthalten
Figure 4: applications of vibration energy with electromagnetic induction
Mechanical transducers are discussed now for the transformation of kinetic energy. This kinetic energy in both translational and rotational forms is formulated as:
Abbildung in dieser Leseprobe nicht enthalten
An analytical model was established [WIL96], and power densities of 1 μW at 70 Hz and 0.1 mW at 330 Hz were reported in experiments. Amirtharajah and Chandrakasan [AMI98] developed a more complicated harvesting device with a test chip, which integrated an ultra-low power controller regulating output voltage within 0.85~0.97 V and a low power sub-band filter digital signal processing (DSP) load circuit. The output power from the harvester could reach 400 μW. Also an electromagnetic harvester was tested in a real automobile producing a peak power of 3.9 mW, however the average power was only 157 μW [GLY04].
A micro-cantilever beam structure has been adopted to induce relative displacement between magnets and a coil bonded at free end of the beam [TOR05]. By using MEMS technique, the silicon beam thickness was only 50 μm. At a 0.06g acceleration and 58.5 Hz resonant frequency, its maximum power and power density could reach 10.8 μW and 900 μW/cm³, respectively. Ching [CHI90] discussed a micro-harvester fabricated on a PCB with total volume of ~1cm³ comprising a lasermicromachined spiral copper spring and an NdFeB magnet and a coil. The peak-to peak 18 output voltage was up to 4.4V and maximum power could reach 830 μW when driven by a 200 μm displacement at its resonant frequency 110 Hz.
Abbildung in dieser Leseprobe nicht enthalten
Table 3: Comparison of different principles
[...]
-
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X. -
Téléchargez vos propres textes! Gagnez de l'argent et un iPhone X.