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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
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
5IPSN 2005
Architecture
6IPSN 2005
Environmental Energy
SolarCharacteristicsSizing considerationsTypically 18mW/cm2 under direct sunlight
Vibration / kinetics Sound / wave Heat
7IPSN 2005
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
15IPSN 2005
Results
16IPSN 2005
Conclusion
Multi-stage + simple hardware + software
==
Perpetual operation
17IPSN 2005
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