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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 - PowerPoint PPT Presentation
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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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