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PROMETHEUS Intelligent Multi-Stage Energy Transfer System for Near Perpetual Sensor Networks Xiaofan...

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PROMETHEUS Intelligent Multi-Stage Energy Transfer System for Near Perpetual Sensor Networks Xiaofan Jiang Joseph Polastre David Culler Electrical Engineering Department University of California, Berkeley Computer Science Department University of California, Berkeley Computer Science Department University of California, Berkeley
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PROMETHEUSIntelligent Multi-Stage Energy Transfer System for Near Perpetual Sensor Networks

Xiaofan Jiang Joseph Polastre David CullerElectrical Engineering DepartmentUniversity of California, Berkeley

Computer Science DepartmentUniversity of California, Berkeley

Computer Science DepartmentUniversity of California, Berkeley

2IPSN 2005

A Typical Solar Powered Sensor Node

Charging Circuit

Voltage Regulation

DAY NIGHT

Stress on Battery

EN

ER

GY

DAY NIGHT NIGHTDAY

3IPSN 2005

Energy Storage Element Designed for Pulsing Applications

Is it enough?

Supercapacitor Medium Capacity High Leakage Infinite recharge cycles

Rechargeable Battery High Capacity Low Leakage 300-500 recharge cycles

vs

4IPSN 2005

Multi-Stage

DAY NIGHT

EN

ER

GY

DAY

DAY NIGHT

Stress on Battery

EN

ER

GY

DAY NIGHT NIGHTDAY

5IPSN 2005

Inefficient and complex hardware? NO!

Simple and efficient hardware

Complete and powerful control using software

Intelligent

6IPSN 2005

Architecture

7IPSN 2005

Environmental Energy

SolarCharacteristicsSizing considerationsTypically 18mW/cm2 under direct sunlight

Vibration / kinetics Sound / wave Heat

8IPSN 2005

Wireless Sensor Node

Duty cycle Intelligence – self-aware of power levels

and able to exert control Ultra-low power – Telos

Low operating voltage

9IPSN 2005

The Larger the Better?

NO!

Without Load With Load

MINIMUM OPERATING VOLTAGE

10IPSN 2005

Secondary Buffer

Li+ vs NiMH Dedicated charging chip vs

software+simple hardware

11IPSN 2005

Case Study: Prometheus

12IPSN 2005

Control Loop and Chargingby SoftwareSensing ADC Piggy-back Voltage divider

trade-offActuation uC I/O Digital switch

Charging Dedicated charging

chip? MOS switch vs Digital

Switch DC/DC current

limiting

13IPSN 2005

Temperature Compensation

14IPSN 2005

Driverpiggy-backed on application active duty cycle

1. if TempV > 2.22. BattV = BattV + 1.45 (TempV − 2.2)3. if CapV < 2.24. SwitchCap = FALSE5. if CapV > 3.56. SwitchCap = TRUE7. if CapV > 4.4 and BattV < 3.58. ChargeBatt = TRUE9. if CapV < 3.810. ChargeBatt = FALSE11. call Radio.send(STATS)

15IPSN 2005

Duty-Cycle Adaptation

16IPSN 2005

Test 1 / Data Reported by TelosScenario: Supercapacitor is less than half full Battery is half full 1% duty cycle No light t0: Source = Cap; Vref = 2.5

Expect: t1: Vref = 1.5

t2: Source = Batt; Vref = 2.5

17IPSN 2005

Result 1

Supercapacitor Battery

t0: Source = Cap

t1: Vref = 1.5

t2: Source = Batt; Vref = 2.5

18IPSN 2005

Test 2 / Actual Measured DataScenario: Supercapacitor very low Battery is half full 1% duty cycle From dark to sunrise t0: Source = Batt

Expect: t1: Source = Cap

t2: Charge = True

t2+dt: Charge = False

19IPSN 2005

Result 2

Supercapacitor Battery

t0: Source = Battt1: Source = Cap

t2: Charge

T2+dt: !Charge

20IPSN 2005

Conclusion

Intelligence + Multi-stage + Simple Hardware

==

Perpetual operation

*

* Direct sunlight


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