Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Power system overview Life in the Atacama Design Review December 19, 2003 J. Teza Carnegie Mellon University

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Power – Simplified Architecture Solar Array MPPT Li Polymer Battery DC/DC Converters Amplifier/ Motors Main DC Bus What is an appropriate battery?

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Simulation – effect of battery capacity Battery capacity: 1500 Wh 1000 Wh 500 Wh Input power Load profile

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Battery - requirements Energy capacity at least 1000 Wh Voltage within requirement of locomotion system (75V < V nominal < 90V) Current capacity sufficient for obstacle climbing Weight less than 15 kg Thermal - operating range 0 to 40 o C Reliability Safety during operation and shipping Cost Schedule

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Battery – trade study TechnologySpecific Energy W/kg $/WhRelative Cost/Wh (practical) Eff %Life cyclesCharge management safetyCan parallel? Sealed lead acid (AGM) –85, CC, equalization; simple Robust, H2 gas explosive Not recommended NiCd CCBurst, leakageno NiMH (7.5) 70500CC, thermal/pressure, dV, dT/dt; complex Overcharge thermal runaway No (?) Li Ion (70) CC CV, voltagefire, leakageyes Li polymer 170 (150 – 200) (39) CC CV, voltageFairly safe, No metallic Li yes

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Battery – implementation Technology / Vendor Configuration / Capacity Battery Mass Cost / Lead time Sealed lead acid (Hawker - Genesis) 16 Ah x 84V 1.3 kWh 44 kg$350 days (COTS) Li Ion (Saft) 31 Ah x 8 x 57 V 2 kWh 17 kg$28K + NRE (?) months (?) Li Polymer (Worley) 3 Ah x 6 x 78 V 1.4 kWh 8 kg$7K / battery + $1.7K controller 6 to 8 weeks

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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: m 3 Mass: 8.2 Kg, plus wiring, fuses, enclosure One module

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Battery – Li Polymer - Cell Capacity dependent on Charge / discharge rate

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Battery – Li Polymer - controller Lithium battery safety unit – Worley LBSU 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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 (?)

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon DC bus nominal – 78V Typical range 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)

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Power - Architecture Solar Array MPPT Li Polymer Battery Controller DC/DC Converters Amplifier/ Motors PMAD Controller DC/DC Converter Li ion Battery Main DC Bus 78V (63 to 88 V) Sub DC Buses … (5, 12, …, 24V)

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Power – Architecture – Shore power CC/CV DC supply Li Polymer Battery Controller DC/DC Converters Amplifier/ Motors PMAD Controller DC/DC Converter Li ion Battery Main DC Bus 78V (63 to 88 V) Shore Power

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Power - Architecture – split solar array DC/DC Converters Amplifier/ Motors PMAD Controller DC/DC Converter Li ion Battery Solar Array MPPT Li Polymer Battery Controller Main DC bus Solar Array MPPT Reduce effect of shadowing and single point failure

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Power – Architecture – battery redundancy DC/DC Converters Amplifier/ Motors Solar Array MPPT Li Polymer Battery Controller PMAD Controller DC/DC Converter Li ion Battery OR diodes drive main DC bus Li Polymer Battery Controller Solar Panels MPPT Reduces chance of system fault due to a battery fault

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Power – Architecture – PMAD Solar Panels MPPT Li Polymer Battery Controller DC/DC Converters Amplifier/ Motors PMAD Controller DC/DC Converter Li ion Battery Main DC Bus 78V (63 to 88 V) V, I CAN bus RS-232 digital analog PMAD control and data acquisition

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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 5V with battery backup for 1 hr in full power mode or 18 hr in low power mode Provision for LCD display

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon 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

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Mechanical – thermal - issues Thermal – ventilation not feasible Maximize conduction dissipation Layout - packaging Cabling Fabrication and field access

Life in the Atacama, Design Review, December 19, 2003 Carnegie Mellon Power – requirements – load Locomotion Motion controller – 9W Motors - Computing Main – 20 W Planning – 30 W Core (PMAD and hibernation) – 5 W Communications Ethernet 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 - ?