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

PROMETHEUS Intelligent Multi-Stage Energy Transfer System for Near Perpetual Sensor Networks. A Battery’s Perspective. Medium Depth of Discharge. ENERGY. Shallow Depth of Discharge. DAY. NIGHT. DAY. A Typical Solar Powered Sensor Node. Charging Circuit. Voltage Regulation. vs.

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

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  1. PROMETHEUSIntelligent Multi-Stage Energy Transfer System for Near Perpetual Sensor Networks

  2. A Battery’s Perspective Medium Depth of Discharge ENERGY Shallow Depth of Discharge DAY NIGHT DAY A Typical Solar Powered Sensor Node Charging Circuit Voltage Regulation

  3. vs Supercapacitor • Medium Capacity • High Leakage • Infinite recharge cycles Rechargeable Battery • High Capacity • Low Leakage • 300-500 recharge cycles Energy Storage Element Designed for Pulsing Applications Is it enough?

  4. AND Intelligent Simple and efficient hardware Complete and powerful control using software Multi-Stage Inefficient and complex hardware? NO!

  5. Architecture

  6. Environmental Energy • Solar • Characteristics • Sizing considerations • Typically 18mW/cm2 under direct sunlight • Vibration / kinetics • Sound / wave • Heat

  7. Wireless Sensor Node • Duty cycle • Intelligence – self-aware of power levels and able to exert control • Ultra-low power – Telos • Low operating voltage

  8. The Larger the Better? NO!

  9. Secondary Buffer • Li+ vs NiMH • Direct from environment vs from primary buffer • Dedicated charging chip vs software+simple hardware

  10. Case Study: Prometheus

  11. Sensing ADC Piggy-back Voltage divider trade-off Actuation uC I/O Digital switch Charging Dedicated charging chip? MOS switch vs Digital Switch DC/DC  current limiting Control Loop and Chargingby Software

  12. Temperature Compensation

  13. Driver PROMETHEUS DRIVER piggy-backed on application active duty cycle 1. if TempV > 2.2 2. BattV = BattV + 1.45 (TempV − 2.2) 3. if CapV < 2.2 4. SwitchCap = FALSE 5. if CapV > 3.5 6. SwitchCap = TRUE 7. if CapV > 4.4 and BattV < 3.5 8. ChargeBatt = TRUE 9. if CapV < 3.8 10. ChargeBatt = FALSE 11. call Radio.send(STATS)

  14. Duty-Cycle Adaptation

  15. Results

  16. Conclusion Multi-stage + simple hardware + software == Perpetual operation

  17. Future Work • Deployment of 1500 nodes equipped with Prometheus for long term observation Questions

  18. 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

  19. 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

  20. Medium Capacity High Leakage Infinite recharge cycles High Capacity Low Leakage 300-500 recharge cycles Primary Buffer vs

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