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

A Battery’s Perspective

EN

ER

GY

DAY

Shallow Depth of Discharge

Medium Depth of Discharge

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

Inefficient and complex hardware? NO!

Simple and efficient hardware

Complete and powerful control using software

AND Intelligent

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Architecture

6IPSN 2005

Environmental Energy

SolarCharacteristicsSizing considerationsTypically 18mW/cm2 under direct sunlight

Vibration / kinetics Sound / wave Heat

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Wireless Sensor Node

Duty cycle Intelligence – self-aware of power levels

and able to exert control Ultra-low power – Telos

Low operating voltage

8IPSN 2005

The Larger the Better?

NO!

9IPSN 2005

Secondary Buffer

Li+ vs NiMH Direct from environment vs from primary

buffer Dedicated charging chip vs

software+simple hardware

10IPSN 2005

Case Study: Prometheus

11IPSN 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

12IPSN 2005

Temperature Compensation

13IPSN 2005

Driver

PROMETHEUS DRIVERpiggy-backed on application active duty cycle1. 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)

14IPSN 2005

Duty-Cycle Adaptation

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Results

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Conclusion

Multi-stage + simple hardware + software

==

Perpetual operation

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Future Work

Deployment of 1500 nodes equipped with Prometheus for long term observation

Questions

18IPSN 2005

Energy - Fundamental Limitation of Sensor Networks How long could current sensor networks

survive without human intervention?

2 to 3 years Why?

Limiting factor storage device

19IPSN 2005

Multi-Stage and Intelligent

- Environmental energy unpredictable buffer battery recharge cycles

- Sensor nodes pulses storage designed for pulsing applications not batteries

- Sensor nodes uC brain can adapt

All these points to … Reduce stress on critical path components Intelligent

20IPSN 2005

Primary Buffer

Medium Capacity High Leakage Infinite recharge

cycles

High Capacity Low Leakage 300-500 recharge

cycles

vs