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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. Charging Circuit. Voltage Regulation. Stress on Battery. ENERGY. DAY. NIGHT. DAY. NIGHT. NIGHT. DAY. A Typical Solar Powered Sensor Node. vs. Supercapacitor Medium Capacity High Leakage

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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. Charging Circuit Voltage Regulation Stress on Battery ENERGY DAY NIGHT DAY NIGHT NIGHT DAY A Typical Solar Powered Sensor Node

  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. Stress on Battery ENERGY ENERGY DAY NIGHT DAY NIGHT NIGHT DAY DAY NIGHT DAY Multi-Stage

  5. Intelligent Simple and efficient hardware Complete and powerful control using software Inefficient and complex hardware? NO!

  6. Architecture

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

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

  9. Without Load With Load MINIMUM OPERATING VOLTAGE The Larger the Better? NO!

  10. Secondary Buffer • Li+ vs NiMH • Dedicated charging chip vs software+simple hardware

  11. Case Study: Prometheus

  12. 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

  13. Temperature Compensation

  14. 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)

  15. Duty-Cycle Adaptation

  16. Test 1 / Data Reported by Telos Scenario: • 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

  17. Result 1 t2: Source = Batt; Vref = 2.5 t0: Source = Cap t1: Vref = 1.5 Supercapacitor Battery

  18. Test 2 / Actual Measured Data Scenario: • 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

  19. Result 2 t0: Source = Batt t1: Source = Cap t2: Charge T2+dt: !Charge Supercapacitor Battery

  20. Conclusion Intelligence + Multi-stage + Simple Hardware == Perpetual operation * * Direct sunlight

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