high-level modelling and performance optimisation of mixed...
TRANSCRIPT
High-level modelling and performance optimisation of mixed-technology
energy harvester systems
Tom J Kazmierski, Leran Wang, Bashir M Al-Hashimi
University of Southampton, UK
MOS-AK, Edinburgh 19 September 2008
2
Energy harvesting in electronics
• State-of-the-art
• Energy harvesting from the environment
• Pervasive computing
3
Vibration-based energy harvester system
AC
Voltage Voltage
booster
• System consisting various components from different physical domains
– Reported equivalent circuit models are inadequate
– VHDL-AMS as modelling language
• Performance loss due to close mechanical-electrical interaction
– Systematic EH optimisation based on HDL model
EH modelling approachesmacro-generator models
4
- Ideal voltage source
- Equivalent circuit
Proposed accurate HDL model
5
- Use VHDL-AMS as modelling language- Describe micro-generator as a series of analytical equations- Mixed-technology (mechanical, magnetic, electrical etc.)
Case study design
• State-of-the-art EH (R. Torah, et.al, Development of a cantilever beam generator employing vibration energy harvesting. In Proceedings of The 6th Int. Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications, 2006.)
•• VibrationVibration--basedbased
•• Electromagnetic microElectromagnetic micro--generatorgenerator
•• Voltage multiplier as boosterVoltage multiplier as booster
•• Super capacitor as storageSuper capacitor as storage
6
Experimental micro-generator
ElectromagneticCantilever basedFixed coil, moving magnetsSmall volume: 150 mm3
7
Micro-generator model
8
• (a)
• (b)
• (c)
B
-B
R
r
(b) Small displacement
z(t)
B
-B
R
r
z(t)
(c) Large displacement
NBtzrtzR **2*))()(( 2222 −+−=Φ
NBtzHrtzHR **)))(())((( 2222 −−+−−−=Φ
NBrR **2*)( +=Φ
Voltage booster
9
• Voltage multiplier as the voltage booster
– 6-stage Villard configuration
– Schottky diodes (BAT760)
0.22FD1 D2 D3 D4 D5 D6
C1
C2
C3
C4 C6
C5
Micro-
generator
Experimental setup
10
• Micro-generator sitting on vibration generator
– Frequency: 50Hz, acceleration level: 0.6 m/s2
• Data collected by LabView
Simulation and verification
11
0
0.5
1
1.5
2
2.5
3
0 30 60 90 120 150
Time (min)
Vo
ltag
e (V
)
Ideal voltage source
Experimental measurementProposed HDL model
Equivalent circuit model
• Different energy harvester models compared with experimental measurements
– Ideal voltage source fails: voltage booster can greatly affect the behaviour of micro-generator
Simulation and verification
12
• Equivalent circuit model is inaccurate:
– L=m, C=1/k, R=b is over simplification
0.8
0.0
-0.81.0
0.0
-1.01.0
0.0
-1.0
Proposed HDL model
Equivalent circuit model
Experimental measurement
Voltage (V)
1200 1220 1240 1260Time (ms)
EH performance optimisation
13
• Performance loss due to mechanical-electrical interaction
– ηLoss=(EHarvested-EDelivered) / EHarvested
• Integrated performance optimisation in VHDL-AMS testbench. (L. Wang and T.J. Kazmierski, VHDL-AMS based genetic optimization of a fuzzy logic controller for automotive active suspension systems, BMAS 2005)
Genetic optimisation in VHDL-AMS testbench
14
• GA parameters:
– 7 genes: 3 from micro-generator, 4 from transformer
– Fitness: super capacitor charging rate v’dot
– Tournament selection
– Elitism
– Arithmetic crossover
– Gene mutation
• Parallel GA: genes in one generation are evaluated simultaneously
• VHDL-AMS finite state machine
EH performance optimisation
15
• Use a voltage transformer as booster
– Optimisation algorithm found that the transformer exhibits better performance than voltage multiplier
Optimisation results
16
Voltage (V)
0 30 60 90 120 150Time (min)
2.0
1.6
1.2
0.8
0.4
0.0
Optimised
Un-optimised
• Super capacitor charging simulation waveforms
Optimisation results
17
Micro-generatorOuter radius of coil (R) 1.2mm
Coil turns (N) 2300Internal resistance (Rc) 1600ΩΩΩΩ
Voltage transformer
Resistance (ΩΩΩΩ) No. of turnsPrimary winding 400 2000
Secondary winding 1000 5000
Micro-generatorOuter radius of coil (R) 1.1mm
Coil turns (N) 2100Internal resistance (Rc) 1400ΩΩΩΩ
Voltage transformerResistance (ΩΩΩΩ) No. of turns
Primary winding 340 1900Secondary winding 690 3800
Un-optimised
Optimised
Further work: automated design flow
18
GA-based performance optimisation
Architecturalsynthesis
Conclusion
19
• Integrated approach to EH modelling and performance optimisation has been developed
• Existing electrical equivalent circuit models of micro-generator cannot predict the voltage booster’s performance accurately
• HDL model based on analytical equations can describe the actual shape and size of an EH
• Through performance optimisation it was possible to increase the energy harvesting rate by 30%