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Power system overview

Power system overview. Life in the Atacama Design Review December 19, 2003 J. Teza Carnegie Mellon University. Power system - function. Sources solar panel shore power Storage daylight operation with reduced insolation night operations (science) hibernation Control

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Power system overview

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  1. Power system overview Life in the Atacama Design ReviewDecember 19, 2003 J. TezaCarnegie Mellon University Carnegie Mellon

  2. Power system - function • Sources • solar panel • shore power • Storage • daylight operation with reduced insolation • night operations (science) • hibernation • Control • operation of subsystems • power distribution • Measurement • engineering logging • health monitoring Carnegie Mellon

  3. Power – Simplified Architecture Solar Array MPPT Main DC Bus DC/DC Converters Li Polymer Battery Amplifier/ Motors What is an appropriate battery? Carnegie Mellon

  4. Simulation – effect of battery capacity Input power Load profile Battery capacity: 1500 Wh 1000 Wh 500 Wh Carnegie Mellon

  5. Battery - requirements • Energy capacity • at least 1000 Wh • Voltage • within requirement of locomotion system • (75V < Vnominal < 90V) • Current capacity • sufficient for obstacle climbing • Weight • less than 15 kg • Thermal - operating range • 0 to 40o C • Reliability • Safety during operation and shipping • Cost • Schedule Carnegie Mellon

  6. Battery – trade study Carnegie Mellon

  7. Battery – trade • Sealed lead acid • Low specific energy • simple, reliable, cheap • NiMH • Fair specific energy • Problems - charge control, cost, reliability, thermal, configuration • Li Ion • Good specific energy • Component and NRE costs, lead time, control, safety • Voltage required makes design complex • Li Ion Polymer • Good specific energy • Reliability / Risk (?) • Cost – limits spares, redundancy Carnegie Mellon

  8. Battery – implementation Carnegie Mellon

  9. Battery – implementation – Li polymer • Worley • Li Polymer • Capacity: 1.4 kWh, 78 V (nominal) • Cost – $18K (two batteries, one controller) • Delivery – 6 (to 8) weeks • Vendor claims no shipping restrictions on assembled battery • Fabrication - Singapore Carnegie Mellon

  10. Battery – implementation – Li polymer • 3.30 Ah (rated) 3.7 V Li polymer cell • Six cell parallel module • Module size : 64 x 100 x 36 mm (approximate) • 21 modules in series • Voltage: 63 to 88.2 V, 78V nominal • Capacity: 19.8 Ah (rated) • Maximum current: 35 A • Battery dimensions: • For example: • 128 x 110 x 378 mm (2 x 1 x 11) • Volume: 0.0053 m3 • Mass: 8.2 Kg, plus wiring, fuses, enclosure One module Carnegie Mellon

  11. Battery – Li Polymer - Cell Capacity dependent on Charge / discharge rate Carnegie Mellon

  12. Battery – Li Polymer - controller • Lithium battery safety unit – Worley LBSU-4-100 • Monitor individual cell voltages • Monitor battery current • Monitor battery temperature • Shut off battery if out of limit condition occurs • Allows external reset of battery (circuit closure) • Allows control of external battery relay • Serial (RS-232) communication • voltage, current, temperature, fault condition reported every minute • Is this control sufficient? One module Carnegie Mellon

  13. Battery – Issues • Reliability • Components, vendor • Single string – no redundancy for computing load • Life cycle – limited (100 – 200 cycles) • Cost – limits redundancy, spares testing • Testing – limits life cycles • Spares – cold or hot? • Fall back / risk mitigation • Substitute other technology (SLA or ?) • Impact of change of technology • Reduction in capacity / increase in mass • Effect on Solar power tracker / solar array requirements (?) Carnegie Mellon

  14. DC bus • nominal – 78V • Typical range - 75.6 to 79.8 V • Maximum range - 63 to 88 V • Issues • Maximum too close to amplifier limit • Switching – light weight components limited • Fusing – circuit breakers (?) or fuses - reliability • Control – solid state relays (typical failure mode for MOSFET is to fail open) Carnegie Mellon

  15. DC sub buses • Typical bus voltages: • 5,12, 24 V • others: 3.3, +/- 12, +/- 15 V • DC / DC converters • Implementation: • Vicor – input 55 to 100V (72V nominal) • High efficiency • 25 to 200 W units, Mega-modules, VI-200 or VI-J00 series • -10 to 40 C temperature, can be paralleled • VI-200 have over-temp and over-current protection • Can be shut down with gate control Carnegie Mellon

  16. Power - Architecture Solar Array MPPT Main DC Bus 78V (63 to 88 V) DC/DC Converters … Battery Controller Li Polymer Battery Sub DC Buses (5, 12, …, 24V) Amplifier/ Motors Li ion Battery PMAD Controller DC/DC Converter Carnegie Mellon

  17. Power – Architecture – Shore power Shore Power CC/CV DC supply Main DC Bus 78V (63 to 88 V) DC/DC Converters Battery Controller Li Polymer Battery Amplifier/ Motors Li ion Battery PMAD Controller DC/DC Converter Carnegie Mellon

  18. Solar Array Solar Array MPPT MPPT Battery Controller Li Polymer Battery Power - Architecture – split solar array Main DC bus DC/DC Converters Amplifier/ Motors Li ion Battery PMAD Controller DC/DC Converter Reduce effect of shadowing and single point failure Carnegie Mellon

  19. Solar Array Solar Panels MPPT MPPT Battery Controller Battery Controller Li Polymer Battery Li Polymer Battery Power – Architecture– battery redundancy OR diodes drive main DC bus DC/DC Converters Amplifier/ Motors Li ion Battery PMAD Controller DC/DC Converter Reduces chance of system fault due to a battery fault Carnegie Mellon

  20. PMAD controller - requirements • Controls • Hibernation of main computer • Power for subsystems – computing, sensors, instruments • Battery controller – reads status and internal values (cell voltage and temps), reset via serial interface • Solar MPPT – via CAN bus interface • Acquires system measurements: • Solar panel, bus voltages and currents • temperatures • Logging on main computer or internally when main computer is off line • Communicates via main computer or external serial port • Has own battery backup • Provides status display on exterior panel of robot Carnegie Mellon

  21. Power – Architecture – PMAD Solar Panels MPPT Main DC Bus 78V (63 to 88 V) V, I V, I DC/DC Converters analog CAN bus analog Battery Controller Li Polymer Battery digital Amplifier/ Motors RS-232 Li ion Battery PMAD Controller DC/DC Converter PMAD control and data acquisition Carnegie Mellon

  22. PMAD controller requirements • I/O required • CAN bus • Serial – three ports • Digital - input / output • opto-isolated • number - TBD • Analog input – range, number TBD • LCD display driver Carnegie Mellon

  23. PMAD controller - implementation • PC104 • Low power CPU • Compact flash • Real time clock • Watchdog timer • Battery backup • Can bus, Digital and analog I/O, serial ports • Operating system - Linux (w/ minimal kernel) • Example system: • Arcom Viper, AIM104-CAN, AIM104-ADC16/IN8, ViperUSP • Total power 4.5W @ 5V with battery backup for 1 hr in full power mode or 18 hr in low power mode • Provision for LCD display Carnegie Mellon

  24. Exterior display / control panel • Displays: • Battery status: charge, discharge, on/off line, fault condition, voltage, current, maximum temperature • Main system state – hibernation, normal, fault • Planner system state – on/off • Controls: • Main power control (manual switch) • Manual reset of battery controller • Manual rest of PMAD controller • Reset / halt of motion controller • Joystick input • E-Stop control Carnegie Mellon

  25. Mechanical - thermal • Ebox – compartmentalization • Battery • Ventilation, isolation, battery change out • Power distribution and locomotion • PMAD (core CPU), MPPT, distribution buses, fuses • Locomotion - Amplifier, motion controller I/O • Computing • Autonomy, planner, motion controller CPU, science computer (?) • Science – provide mechanical support, power, communication for: • Chlorophyll detector • Fluorescence camera • VisNIR spectrometer • Additional instruments Carnegie Mellon

  26. Mechanical – thermal - issues • Thermal – ventilation not feasible • Maximize conduction dissipation • Layout - packaging • Cabling • Fabrication and field access Carnegie Mellon

  27. Power – requirements – load • Locomotion • Motion controller – 9W • Motors - • Computing • Main – 20 W • Planning – 30 W • Core (PMAD and hibernation) – 5 W • Communications • Ethernet - 6.3 W • Low BW - ? • Sensing • Nav pair – 3W • SPI pair – 3W • Localization – FOG 3W, SBC 2.2W • Crossbow Tilt sensor – 0.24W • Pan/tilt – 18W (operating) • Workspace cams – ? • Sick laser – 17W • Novatel GPS – 12W • Science • Chlorophyll - ? • VisNIR – 50W ? • Plowing - ? Carnegie Mellon

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