F1 micropower

Wireless Embedded Systems and Networking Foundations of IP-based Ubiquitous Sensor Networks Micro-Power Systems : 

Wireless Embedded Systems and Networking Foundations of IP-based Ubiquitous Sensor Networks Micro-Power Systems David E. Culler University of California, Berkeley Arch Rock Corp. July 13, 2007

Micro-Power System Architecture: 

Micro-Power System Architecture Evaluation Metrics Effsolar = Pon / PmaxP Effsystem = (EL1+ … + ELn + Econs) / Esol

An Example: 

An Example Solar energy scavenging system for Telos Super capacitors buffer energy Lithium rechargeable battery as a backup Uses MCU to manage charge cycles to extend system lifetime Manage limited recharges Simple, carefully developed design Redesigned for TRIO deployment Boosting and current limiting Developed reactive power management software architecture Demonstrated in REALITY Prometheus Design estimates Perpetual Environmentally Powered Sensor Networks, Jiang, Polastre, Culler, IPSN/SPOTS, 2005

Facts: 

Facts E = P * T

Energy Storage: 

Energy Storage

Energy and Power Density: 

Energy and Power Density

Battery Chemistry: 

Battery Chemistry

Energy Stroage: 

Energy Stroage Requirements: Lifetime, Capacity, Current draw, Size/Weight Types of storage: NiMH: capacity and cost Li+: energy density and capacity Supercap: lifetime Storage configuration: Combination of battery and supercap provides good lifetime as well as capacity. Charging mechanisms: HW vs. SW, Complexity vs. Efficiency

The Load: 

The Load

Load (Sensor Node):Estimating Node Consumption: 

Load (Sensor Node): Estimating Node Consumption Energy consumption with radio comm: Iest = R*Iawake + (1-R) * Isleep

The Ambient Source: 

The Ambient Source Solar Vibration Movement Flow Heat transfer

External Environment:Estimating Solar Radiation: 

External Environment: Estimating Solar Radiation Statistical Model Mathematical Model

Solar Collector:Solar-cell Characteristics: 

Solar Collector: Solar-cell Characteristics Solar-cell I-V curve Regulator

Charging to Energy Storage Element: 

Charging to Energy Storage Element Supercap for primary, lithium-ion for secondary. Reduces battery charging frequency. Software-controlled battery charging. Unlike other batteries, Li+ battery should be charged only when there is sufficient charge in the supercap. Pros: Simple hardware: micro-controller, DC-DC converter, analog switch. Cons: Requires correct software for charging control.

Consideration of other types of storage element: 

Consideration of other types of storage element Battery is needed during overcast days. Supercap-only method doesn’t have sufficient capacity. Comparison of charging efficiency is not available yet.

Comparative Study:Solar-Collector Operation: 

Comparative Study: Solar-Collector Operation Compare Pon with PmaxP solar-cell operating point maximum possible value Trio Pon – PmaxP = 4.83mW (5.3%) Heliomote Pon – PmaxP = -16.75mW (-23.2%)

Comparative Study:Energy flow and efficiency: 

Comparative Study: Energy flow and efficiency Compare mote consumption (Econs) and stored energy (Ebat and Ecap) with solar energy income (Esol). Trio: up to 33.4%, Heliomote: up to 14.6%

Solar-Collector Operation: Trio: 

Solar-Collector Operation: Trio

Solar-Collector Operation: Heliomote: 

Solar-Collector Operation: Heliomote

Energy flow and efficiency (Heliomote)- Energy loss due to regulator: 

Energy flow and efficiency (Heliomote) - Energy loss due to regulator Solar energy income: 08:00 to 17:00. Clipped after 12:00. Two-third loss in daily energy income.

Related Work on Solar Powered Sensor Network: 

Related Work on Solar Powered Sensor Network Trio [DHJ+06] Real deployment of large sensor nodes. Multi-hop routing. Operate only for several hours with full radio cycle. Other Previous Works RF transmit beacon [ROC+03], Prometheus [JPC05] Heliomote [RKH+05], ZebraNet [ZSLM04]

Energy Management Architecture: 

Energy Management Architecture