Energy Harvesting and Applications
description
Transcript of Energy Harvesting and Applications
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Energy Harvesting and Applications
D. J. Inman A. Erturk, M.A. Karami, C. DeMarqui, S. Anton, B. Joyce, J. Hobeck and Y. Wang
Center for Intelligent Material Systems and StructuresNSF I/UCRC Center for Energy Harvesting Materials and Systems
Virginia TechBlacksburg, VA 24061, USA
[email protected] www.cimss.vt.eduand
Institute for Smart TechnologiesUniversity of BristolBristol, BS* 1TR [email protected]
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OutlineIntroduction to the basics in energy harvestingSelf charging structuresEnhancements to vibration based energy harvesting using nonlinear dynamics (Erturk)
Piezomagnetic harvesting from a bistable beamPiezoelectric harvesting from a bistable plate
Piezoaeroelastic energy harvesting (Erturk and DeMarque)HarvestingSimultaneous harvesting and flutter suppression
Minimum energy controllers to work with harvesters (Wang)Application to Bridge Monitoring
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Energy Harvesting as used here refers to: Capturing low levels of ambient waste energy to convert to useable electrical energyThe goals are:
To increase battery life or to replace batteriesTo provide wireless sensor solutions to numerous problems
Most of the effort reported here focuses on harvesting mechanical vibration using the piezoelectric effectOther important harvesting mechanisms are
Use of the Seebeck effect using thermoelectric materials to capture thermal gradientsUse of the photovoltaic effect to capture solar energy
Other effects useful in harvesting mechanical energy are the electromagnetic effect and the electrostatic effect
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Some Sample Numbers
Mechanical Harvesting from ambient vibration produces values from milliwatts to microwatts. (eg 0.5 g at 8 Hz produces 10 mW)Small thermal electrics and solar can produce up to a few wattsSmall solar arrays can also produce of the order of a watt
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Piezoelectric based Energy Harvesting Involves 4 Components
Structural Dynamics
PiezoelectricConstitutive laws
Electric Circuits
wtt (x,t)+ Lw(x,t) = f(x,t)Bw =0
€
S=sET+dED=dT+εTE
v + iR =0
Storageand/or direct use
Linear Cantileverswith tip masses well Studied and modeled
Room here for advancesin material science
Need adaptive and nonlinear circuits to address issues of conditioning and optimalityMost studies focus on just optimal resistance
Batteries Li IonSuper capsMechanical not much investigated
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The piezoelectric effect couples mechanical strain to and electric field allowing for both sensing and actuation functions
y
x
xixi+1
Host structure
Piezoceramic
Neutral axisb
t
y1 y2
The constitutive equations are
S =sET + dED =dT + εTE
S is the strain, T is the stress, D is the electric displacement, E is the electric field, sE is the compliance measured at a constant electric field, eT is the permittivity measured at constant stress and d is the charge coefficient.
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Harvesting vibration using the piezoelectric effect can be configured in a number of ways
1. Layered onto a structure2. Cantilevered off of a vibrating mounting point (with tip mass)3. Stacked between two moving surfaces4. Flapping in the wind5. ????
Cantilevered with tunable tip mass: Tip mass
PZT
Moving base
Layered into a structural member:
PZT
Proof mass
Bimorph vs. unimorph
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Storage and Duty Cycles can extend the usefulness of harvested energy
Not all applications need continuous powerStorage devices can be used to enhance the usefulness of a harvesting systemSuppose telemetry of a sensor signal is required 1 sec out of every hour (following example illustrates)
Storage can be through batteries or capacitorsBatteries: limited cycles/hold charge wellCapacitors and super capacitors: large numbers of cycles, drain quickly
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Most harvesting of vibration using the piezoelectric effect is based on the idea of resonance using a cantilever
Cantilevered with tunable tip mass:
Tip mass
PZT
Moving base
xp (t) =f0
(w n2 −w 2)2 + (2ζw n)
2sinwt
F sinwt
wn =km
Response:
Natural frequency of structure:
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Internal (strain rate) damping
External (air) damping Electrical term
Inertial excitation External damping excitation
Distributed Parameter Model (Erturk & Inman)
Internal capacitance of the piezoceramic Circuit
excitation term
Coupled electrical circuit equation:
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Steady state voltage response:
Steady state vibration response:
Closed form solution for both the mechanical and electrical response reveals backwards coupling
Backward piezoelectric coupling in the beam response (clearly not an electrically induced viscous damping term)
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Cantilever based energy harvesting in the linear region results in a single frequency device
Power out versus frequency of disturbance for a linear harvester
Issues: ambient energy is often broad band in the low frequency range, linear harvesting is narrowband, and frequency increases as the length of the cantilever decreases
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Here we exploit nonlinear effects to increase the band width of the energy harvester
Nonlinear behavior is purposefully introduced using added magnets to encourage harvesting over a broader frequency range
Once completed the power generated by the linear and nonlinear system are compare for exactly the same ambient input signal
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Limit Cycle Oscillations for Broad Band HarvestingA magnetic field causes the equation of motion of the harvesting piezoelectric cantilever to be nonlinear
Spacing of the magnets results in:5 equilibrium (3 stable)3 equilibrium (2 stable)1 equilibrium (1 sable)
Limit cycle oscillation is the possible producing large amplitude periodic response over a range of input frequencies
&&x + 2ζ &x−12x 1−x2( )−χv=fχosΩt
&v+ λv+κ &x =0
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NONLINEAR EFFECTS: Bistable Beam Induces More Power Over Wider Frequency Range
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Illustration of Limit Cycle Harvesting for low and high amplitude accelerations
8.5 mW at 0.35g an order of magnitude better then w/o magnets!
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Comparison of voltage vs velocity vs time of linear and nonlinear harvesters for increasing frequency
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Power Output Comparison of Linear vs Nonlinear
Excitation Frequency
5 Hz 6 Hz 7 Hz 8 Hz
Piezo-Magneto-
Elastic
1.57 mW 2.33 mW 3.54 mW 8.54 mW
Piezo-elastic 0.10 mW 0.31 mW 8.23 mW 0.46 mW
Linear Resonance
Note that at linear resonance the linear system will always win, however it is narrow band and falls off quickly away from resonance and that the nonlinear has higher values overall
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Such nonlinearities can also be induced by using a bistable plate
Bistable carbon-fiber plate with piezoceramic patches
The plate is clamped to a seismic shaker from its center point.
Arrieta, A.F., Erturk, A., Hagedorn, P., and Inman, D.J., 2010, A Piezoelectric Bi-stable Plate for Nonlinear Broadband Energy Harvesting, Applied Physics Letters (in press).
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Various nonlinear phenomena can be observed in the bistable plate, enhancing harvesting.
Chaos (12.5 Hz)
High-energy LCO (8.6 Hz)Voltage history samples
Intermittency (9.8 Hz)
Arrieta, A.F., Erturk, A., Hagedorn, P., and Inman, D.J., 2010, A Piezoelectric Bi-stable Plate for Nonlinear Broadband Energy Harvesting, Applied Physics Letters (in press).
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Large-amplitude oscillations generate very high power output over a range of frequencies.
Average power vs. Frequency
Average power vs. Load resistance
(98.5 kohm)
Arrieta, A.F., Erturk, A., Hagedorn, P., and Inman, D.J., 2010, A Piezoelectric Bi-stable Plate for Nonlinear Broadband Energy Harvesting, Applied Physics Letters (in press).
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Application of energy harvesting to Structural Health monitoring
The goal is to provide power for remote monitoring systems so that battery life can be extended and or batteries can be removedThree applications are under way
One is monitoring in flowsOne is the monitoring of a bridgeThe last is the monitoring of a wind turbine blade
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Piezoelectric Grass for Harvesting Energy from a Flow for Running Remote Sensors
In line configuration Staggered configuration
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3-span steel girder bridge (08/18/09 - Roanoke)
Approximation as a persistent single harmonic (0.05g at 7.7 Hz)
Acceleration signal measured on the bridge
Acceleration data of the bridge has been simplified to a harmonic function for simulations in the lab.
Seismic shaker
Accelerometer
Piezoelectric and electromagnetic generators
Acceleration measured on the shaker
Experimental setup
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Piezoelectric and electromagnetic power outputs have been measured for an acceleration input of 0.05g (RMS: 0.035g) at 7.7 Hz.
Piezoceramic patches
Accelerometer
Seismic shaker
Rare earth magnets
Combined piezoelectric-electromagnetic generator configuration
Coil
Electromagnetic part : 0.22 V for 82 ohms = 0.6 mW (per coil)
Piezoelectric part : 11.2 V for 470 kohms = 0.3 mW
Power output of a single generator (for 0.05g) = 0.9 mW
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Increased base acceleration amplitude results in a larger power output. (0.1g, RMS: 0.07g at 7.7 Hz yields 2.7 mW).
Electromagnetic part : 0.42 V for 100ohms = 1.8 mW (from a single coil)Piezoelectric part : 21 V for 470 kohms = 0.94 mW
Power output of a single generator (for 0.1g) = 2.7 mW
[click on the movie]
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Compact Contact-less prototype has been fabricated and is waiting to be tested
Magnet rotor needs to be matched with blade rotor output profile
Multiple blade geometries have been printed
Piezoelectric Low Speed Wind Harvester
Hope to gather wind speeds at a few kmh
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Example of how Energy harvesting enables other technologies: Monitoring of wind turbines
Impact Impact or cracking detected via Acoustic Emission (AE) Signals activated periodically
and/or by impact.
NO Sleep
YES
Impedance activated via AE and periodically
to see if significant damage exists
NO Sleep
YESBroadcast damage state
Fatigue
SensorData
Blade Energy
Energy harvesting from blade vibration and centripetal force
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Uses the interplay between gravity and centripetal force to harvest energy
-10 -5 0 5 10-10
-8
-6
-4
-2
0
2
4
6
8
10
Path of magnet
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Sample of energy harvesting capability for wind turbine blades
0 1 2 3 4 5 6 7 8 9 100
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
Time t, s
Load
Voltage
, Volts
Model w/o SpringData
Voltage versus time
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Prospects of using harvested energy to perform Control
1. The first example is harvesting energy from low induced wing vibrations in an aircraft wing• This action of harvesting automatically induces a
shunting effect which acts a a vibration suppression system
• The result is an increase in flutter speed whilst simultaneously harvesting energy
2. The second is a look at performing active control using only harvested energy to provide vibration suppression.• As a first step, we examine which control laws for
vibration suppression will use the least amount of energy
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Flow Induced Energy HarvestingTypical section with piezoceramics
Experimental setup
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Flow Induced Energy Harvesting ResultsPiezoaeroelastic equations
Model validation – piezoaeroelastic response
at the flutter boundary
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Total damping vs. Airflow speed
Tip displacement
Electrical power
De Marqui, Jr., C., Erturk, A., and Inman, D.J., 2010, Piezoaeroelastic Modeling and Analysis of a Generator Wing with Continuous and Segmented Electrodes, Journal of Intelligent Material Systems and Structures, 21 (in press) doi: 10.1177/1045389 X10372261.
The time-domain piezoaeroelastic solution can predict the electromechanical response for airflow speeds below the linear flutter speed.
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Predictions for wing based harvesting and passive control
The analytical model predicts that the piezoaeroelastic system will harvest 10.7 mW at an air speed of 9.32 m/s
The shunting effect of the energy harvester simultaneously adds damping to the system and predicts an increase in flutter speed of 5.5% (that is a reduction in vibration)
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Examination of Low Power Control Laws
The goal is to find the feedback control law for vibration suppression the uses the least amount of energy
Fix the performance by fixing the settling time and overshoot and then computing several different control laws to obtain the desired response and then comparing the energy required for each
Hu(t) x(t)
Controller
G
_r(t) Plant
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Proposed Hybrid Control Laws
Use several common vibration suppression controllers,then use a switching algorithm over the top:
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The response of four controllers and their hybrid implementation
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2-5
0
5
Time(s)--(a)
Dis
p.( m
m)
0 0.5 1 1.5 2-5
0
5
Time(s)--(b)
Dis
p.( m
m)
0 0.5 1 1.5-5
0
5
Time(s)--(c)
Dis
p.(m
m)
0 0.5 1 1.5 2-5
0
5
Time(s)--(d)
Dis
p.( m
m)
0 0.5 1 1.5 2-5
0
5
Time(s)--(e)
Dis
p.(m
m)
Open-loop
PPFBang-bang-PPF
PIDBang-bang-PID
NonlinearBang-bang-nonlinear
LQRBang-bang-LQR
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Power consumption for each of the 8 controllers
0 0.2 0.4 0.6 0.80
50
100
150
200
Time(s)(a)
Inst
.Pow
er(m
W)
0 0.2 0.4 0.6 0.80
50
100
150
200
Time(s)(b)
Inst
.Pow
er( m
W)
0 0.2 0.4 0.6 0.80
50
100
150
200
Time(s)(c)
Inst
.Pow
er(m
W)
0 0.2 0.4 0.6 0.80
50
100
150
200
Time(s)(d)
Inst
.Pow
er( m
W)
PPFBang-bang-PPF
PIDBang-bang-PID
NonlinearBang-bang-nonlinear
LQRBang-bang-LQR
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Summary of the average power used by each controller (experimental):
The best choice of controller for use with harvested energy
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SELF CHARGING STRUCTURES AND COMBINED EFFECTS: piezoelectric, solar and thermal energy harvesting with flexible thin-film batteries.
Aluminum substructure components
Flexible thin-film battery
Piezoceramic patch
Flexible solar panel
Heat sink
Thermoelectric generator
Heater
New generation self-charging structures with flexible piezoceramic, solar panel and battery layers
Thermoelectric generator
Thermal power
Vibration power
Solar power
Thin-film battery
Regulator circuit for
impedance matching
Efficient circuit design for battery charging
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Extending the concept of the self charging structure to solar and thermal energy harvesting
Thermoelectric generator
Piezoelectric transducer
Flexible solar panels
Thin film Battery
70 mW
30 mW/g2
10 mW
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3.E/M CHARACTERIZATION: of the multifunctional system for different vibration, solar and thermal energy levels.
Different stages of fabrication
Aluminum (innermost) Flexible solar panel
(outermost)
Thin-film battery
Base excitation using a shaker
Solar power (outdoor) Thermal power Vibration power at resonance
Load resistance [ohms]
Pow
er [m
W]
Tem
pera
ture
[o C]
Load resistance [ohms]
Power [m
W]
hot side
cold side
temperature difference
power output
Piezo layer
Assembly: 4” x 1” x 0.06”
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Circuits and Implementation
Thermoelectric Harvester
PZT vin
+
-
iin
vS
+
-vo
io
iL
Ld Co Ro
Rin+
-
R1
R2
R3
RC1
RC2CC
vL
+
-
Cin
M
D
DC
vin
+
-
iin
vo
io
iL
Ld Co Ro
Rin+
-
R1
R2
R3
RC1
RC2CC
vL
+
-
Cin
M
D
DC
Solar/TEG
vin
+
-
iin
vo
io
iL
Ld Co Ro
Rin+
-
R1
R2
R3
RC1
RC2CC
vL
+
-
Cin
M
D
DC
Solar/TEG
Piezoelectric Harvester
Solar Harvester
Switching Impedance Matching Circuits
Thin-film Battery #1
Thin-film Battery #2
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UAV APPLICATION: embed piezoelectric and thin-film battery into the wing spar of a UAV to form a multifunctional spar capable of powering a local sensor
Multifunctionality Load bearing + Power generation + Energy storage
Self-charging structuresembedded in wing spar
Low-power sensor node being powered locally by harvesting system
• Incorporate energy harvesting devices and novel storage elements into UAVs.
• Provide local power source for low-power sensors in aircraft
• Flight endurance should remain unchanged with addition of harvesting
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Low Frequency MEMS Cantilever Harvesting
MEMS scale demands a cantilever of short lengthThe resonance frequency of a cantilever is inversely proportional to the square of its length: short beams mean high frequenciesAmbient energy in most systems are lowA potential solution is to use a zigzag arrangement of cantilevers
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Reduction in frequency with member increase and experimental validation of model
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3 mm
3 mm
300 um
1.45 mm
300 um~ 550 Hz, 20 nw/g2
~ 380 Hz, 35 nw/g2
~400 Hz
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Five popular piezoelectric ceramics have been considered (PZT-5A, PZT-5H and 3 single crystal types).
An order of magnitude difference for the d31 values of single crystals is not the case for their effective e31 values due to the effect of elastic compliance.
Compliance|d31|
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Comparison of these 5 Bimorph Cantilevers:For resonance excitation, the peak power does NOT differ by an order of magnitude as d31 does.
For different dynamic flexibilities at resonance, the peak power for resonance excitation does not depend much on d31 .
When the dynamic flexibilities of the bimorphs are artificially made identical, the maximum power outputs for resonance excitation become very similar. Larger power outputs of the single crystal bimorphs are due to their larger dynamic flexibilities (rather than their very large d31 constants).
Mechanical damping (hard to control due to clamping conditions and adhesive layers) can change the entire pictureModifications in the harvester’s geometry might be much more effective than the type of active material used.
Bimorph with larger d31 gave less power!
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Effect of the material properties of PZT for Harvesting Applications
It has been observed from the theory that d31 never appears solely and is always in multiplication with the elastic stiffness (importantly, larger d31 of single crystals comes with lower elastic stiffness – hence the effective e31 values have the same order of magnitude).
The dynamic flexibility and mechanical damping of a piezoelectric energy harvester can be much more important than the active material being used.
Dynamic flexibility of a piezoelectric energy harvester basically depends on the mechanical design. It is more difficult to control the mechanical damping due to clamping conditions and/or adhesive layers (and it should be noted that mechanical damping can change the entire picture!..).
These results might help those in the material side of piezoceramic development produce better materials for harvesting.
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Summary and ConclusionsIntroduced the concepts of harvesting ambient waste energy vibrationIllustrated how nonlinearity can be used to enhance energy harvestingPresented several examples of the usefulness of harvesting such low level energyTo review most applications are in charging batteries for sensor type applications (wireless sensing and monitoring)Its not safe the world renewable energy but rather “save the batteries” level and is an enabling technology for wireless systems
Thanks for your attention (sponsors follow)
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Acknowledgements
Questions/comments?
The support from the US Air Force Office of Scientific Research MURI under grant number F 9550-06-1-0326 “Energy Harvesting and Storage Systems for Future Air Force Vehicles” and “Simultaneous Vibration Suppression and Energy Harvesting” Grant number FA9550-09-1-0625, both monitored by Dr. B. L. Lee and the US National Institute of Standards and Testing is gratefully acknowledged.
The authors also gratefully acknowledge the support of CAPES (Brazil) and the GR Goodson Professorship Endowment.