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Limits of Life in the Atacama: Investigation of Life in the Atacama Desert of Chile

Limits of Life in the Atacama: Investigation of Life in the Atacama Desert of Chile. Power System Design James Teza The Robotics Institute Carnegie Mellon University. Outline. Introduction Current Configuration Requirements Components - Development Schedule Summary.

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Limits of Life in the Atacama: Investigation of Life in the Atacama Desert of Chile

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  1. Limits of Life in the Atacama: Investigation of Life in the Atacama Desert of Chile Power System Design James TezaThe Robotics InstituteCarnegie Mellon University Carnegie Mellon

  2. Outline • Introduction • Current Configuration • Requirements • Components - Development • Schedule • Summary Carnegie Mellon

  3. Current Configuration of Hyperion • Design constraints • 24 hour sun synchronous operation • 24 hour insolation • Relatively benign environment and terrain • Primary power source – solar • Battery storage – power leveling Carnegie Mellon

  4. Current Configuration of Hyperion • Batteries – sealed lead acid • System bus voltage – 24 VDC • Constrained by existing motor amplifiers and DC/DC converters • Maximum power point trackers (MPPT) • Support lead acid batteries only • Provided no external control or data • Not protected from over voltage fault conditions • System loads cannot be switched • Power system monitoring not accurate Carnegie Mellon

  5. Current Configuration of Hyperion • Solar power • 320 Seimens Si cells on custom fabricated modules • 8 detachable modules • Fixed array with adjustable angle along roll axis • 3.4 m2 total array area Carnegie Mellon

  6. Requirements – Atacama vs. Haughton • Environment – less benign than Haughton • Rougher terrain • higher obstacle density • larger obstacles • Higher wind speeds • Dust • Greater thermal extremes • Insolation • Maxima higher in Atacama than Haughton • Greater diurnal extremes (irradiance and angle) • No requirement for sun synchrony but resource cognizance required • Power budget will be driven by task and distance schedules • Longer duration of operation Carnegie Mellon

  7. Requirements – Goals • Improved power efficiency • Higher efficiency solar cells – smaller array • Higher bus voltage – more efficient motors • Higher battery storage efficiency – extend operating time, reduce battery mass • Better vehicle stability • Smaller array area – less wind loading and • lower CG • More accurate system monitoring • Better instrumentation • Better battery and system models • Capable of entering low power mode(s) via selective load switching • Reliable system capable of extended operation Carnegie Mellon

  8. Requirements - Power Budget Note: does not assume overlapping of tasks Carnegie Mellon

  9. Requirements - Power Budget Daily energy requirement based on proposed activity schedule Carnegie Mellon

  10. Requirements – Power Budget Daily energy available Carnegie Mellon

  11. Quantum efficiency (ATJ vs. TJ) ATJ ATJ ATJ TJ TJ TJ InGa Ge InGaAs 100 90 80 70 60 50 Quantum Efficiency (%) 40 30 20 10 0 300 500 700 900 1100 1300 1500 1700 Wavelength (nm) Components – Solar cells • Emcore advanced triple junction (ATJ) cells • 27.7% average efficiency specified at AM0 • Expect equal or higher efficiency at AM1.5 • Thermal effect • Greater dependence on spectra (air mass) • Series (cascade) junctions • InGa junction limits current with reduced UV Carnegie Mellon

  12. Components – Solar cells Predicted Insolation Spectra Carnegie Mellon

  13. Components - Solar cells • Component testing • Fabricate prototype array using Emcore ATJ cells for field tests • Gather Isc, Voc and spectrophotometric data • Perform initial testing in Phoenix, Arizona (winter ’02) • First year field testing in Chile (’03) • Actual efficiency TBD during year 1 component testing Carnegie Mellon

  14. Components - PMAD • Modify existing power system micro controller to provide increased capability • Greater system monitoring accuracy • Battery state • Insolation • Internal environment (temperature) • Load switching for low power mode or modes • Reliable hibernation mode • Able to switch off main CPU and re-start system reliably • Improve battery and system models Carnegie Mellon

  15. Components - Batteries • Sealed Lead Acid • Relatively low energy density (25 to 40 Wh/kg, 33 Wh/kg for Hyperion) • Relatively cheap • Robust • Relatively simple battery model • Li-Ion • High energy density (120 to 200 Wh/kg) • Expensive (between 5 to 10 x cost of lead acid) • Control of charge / discharge limits required • Safety considerations • More complex battery model Carnegie Mellon

  16. Components - MPPT • HTA Biel design MPPT • Higher efficiency • Communication via CANBus • Open software • Suitable with sealed lead acid and Li-ion battery systems • Input and output protection Carnegie Mellon

  17. Development – Issues • Solar panel configuration • Horizontal panel orientation • Lower panel position • Integrate panel with enclosure • Thermal control • Provide cooling • Seal against dust • High reliability in hostile environment Carnegie Mellon

  18. Development - Schedule • Year 1 • Integrate on robot: • PMAD • Component testing in Chile: • Advanced triple junction cells • Component testing: • Improved MPPT • Li ion batteries • High bus voltage components • (new motor amplifiers, motors and DC/DC converters) • Year 2 • Integrate on robot: • Advanced triple junction cells • Improved MPPT • Li ion batteries • High bus voltage components Carnegie Mellon

  19. Summary • Improve system efficiency • ATJ solar cells • Improved MPPT • Li batteries • Higher bus voltage and components • Improve vehicle stability • Smaller array area, lower CG • Improve power system monitoring and models • Implement power system control • Resolve issues • panel configuration, thermal control, reliability Carnegie Mellon

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