life in the atacama, design review, december 19, 2003 carnegie mellon power system overview life in...

Carnegie MellonLife in the Atacama, Design Review, December 19, 2003

Power system overview

Life in the Atacama Design ReviewDecember 19, 2003

J. TezaCarnegie Mellon University


Power system - function

Sourcessolar panelshore power

Storagedaylight operation with reduced insolation night operations (science) hibernation

Control operation of subsystemspower distribution

Measurementengineering logginghealth monitoring


Power – Simplified Architecture

SolarArray

MPPT

Li PolymerBattery

DC/DCConverters

Amplifier/Motors

Main DC Bus

What is an appropriate battery?


Simulation – effect of battery capacity

Battery capacity: 1500 Wh 1000 Wh 500 Wh

Input power Load profile


Battery - requirements

Energy capacityat least 1000 Wh

Voltagewithin requirement of locomotion system

(75V < Vnominal < 90V)

Current capacitysufficient for obstacle climbing

Weightless than 15 kg

Thermal - operating range 0 to 40o C

ReliabilitySafety during operation and shippingCostSchedule


Battery – trade study

Technology Specific Energy W/kg

$/Wh Relative Cost/Wh(practical)

Eff % Life cycles Charge management

safety Can parallel?

Sealed lead acid

(AGM)

35-40 0.2-0.3 1 50–85,

70

200-500 CC, equalization; simple

Robust, H2 gas explosive

Not recommended

NiCd 30-60 0.5 2 72 1500 CC Burst, leakage no

NiMH 60-80 0.7 2.8

(7.5)

70 500 CC, thermal/pressure, dV, dT/dt; complex

Overcharge thermal runaway

No (?)

Li Ion 110 -135 4

(70)

96 500-1000 CC CV, voltage fire, leakage yes

Li polymer 170

(150 – 200)

1.15 3.6

(39)

98 150-200 CC CV, voltage Fairly safe,

No metallic Li

yes


Battery – trade

Sealed lead acidLow 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


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 (?)

2 - 6 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


Battery – implementation – Li polymerWorley

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


Battery – implementation – Li polymer3.30 Ah (rated) 3.7 V Li polymer cellSix cell parallel moduleModule size : 64 x 100 x 36 mm (approximate)21 modules in series Voltage: 63 to 88.2 V, 78V nominalCapacity: 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


Battery – Li Polymer - Cell

Capacity dependent onCharge / discharge rate


Battery – Li Polymer - controller

Lithium battery safety unit – Worley LBSU-4-100Monitor individual cell voltages Monitor battery currentMonitor battery temperature

Shut off battery if out of limit condition occursAllows 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


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 (?)


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)


DC sub buses

Typical bus voltages:5,12, 24 Vothers: 3.3, +/- 12, +/- 15 V

DC / DC convertersImplementation:Vicor – input 55 to 100V (72V nominal)High efficiency25 to 200 W units, Mega-modules, VI-200 or VI-J00 series-10 to 40 C temperature, can be paralleledVI-200 have over-temp and over-current protectionCan be shut down with gate control


Power - Architecture

SolarArray

MPPT

Li PolymerBattery

BatteryController

DC/DCConverters

Amplifier/Motors

PMADController

DC/DCConverter

Li ionBattery

Main DC Bus 78V (63 to 88 V)

Sub DC Buses

…

(5, 12, …, 24V)


Power – Architecture – Shore power

CC/CVDC supply

Li PolymerBattery

BatteryController

DC/DCConverters

Amplifier/Motors

PMADController

DC/DCConverter

Li ionBattery


ShorePower


Power - Architecture – split solar array

DC/DCConverters

Amplifier/Motors

PMADController

DC/DCConverter

Li ionBattery

SolarArray

MPPT

Li PolymerBattery

BatteryController

Main DC bus

SolarArray

MPPT

Reduce effect of shadowing and single point failure


Power – Architecture – battery redundancy

DC/DCConverters

Amplifier/Motors

SolarArray

MPPT

Li PolymerBattery

BatteryController

PMADController

DC/DCConverter

Li ionBattery

OR diodes drive main DC bus

Li PolymerBattery

BatteryController

SolarPanels

MPPT

Reduces chance of systemfault due to a battery fault


PMAD controller - requirements

Controls Hibernation of main computerPower for subsystems – computing, sensors, instrumentsBattery controller – reads status and internal values (cell voltage and temps), reset via serial interfaceSolar MPPT – via CAN bus interface

Acquires system measurements:Solar panel, bus voltages and currentstemperatures

Logging on main computer or internally when main computer is off lineCommunicates via main computer or external serial portHas own battery backupProvides status display on exterior panel of robot


Power – Architecture – PMAD

SolarPanels

MPPT

Li PolymerBattery

BatteryController

DC/DCConverters

Amplifier/Motors

PMADController

DC/DCConverter

Li ionBattery


V, I

V, I

CAN bus

RS-232

digital

analog

analog

PMAD controland data acquisition


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


PMAD controller - implementation

PC104Low power CPUCompact flashReal time clockWatchdog timerBattery backup Can bus, Digital and analog I/O, serial portsOperating system - Linux (w/ minimal kernel)Example system:Arcom Viper, AIM104-CAN, AIM104-ADC16/IN8, ViperUSPTotal power 4.5W @ 5V with battery backup for 1 hr in full power mode or 18 hr in low power modeProvision for LCD display


Exterior display / control panel

Displays:Battery status: charge, discharge, on/off line, fault condition, voltage, current, maximum temperatureMain system state – hibernation, normal, faultPlanner system state – on/off

Controls:Main power control (manual switch)Manual reset of battery controllerManual rest of PMAD controllerReset / halt of motion controllerJoystick inputE-Stop control


Mechanical - thermal

Ebox – compartmentalizationBatteryVentilation, isolation, battery change out

Power distribution and locomotionPMAD (core CPU), MPPT, distribution buses, fusesLocomotion - Amplifier, motion controller I/O

ComputingAutonomy, planner, motion controller CPU, science computer (?)

Science – provide mechanical support, power, communication for:Chlorophyll detectorFluorescence cameraVisNIR spectrometerAdditional instruments


Mechanical – thermal - issues

Thermal – ventilation not feasible

Maximize conduction dissipation

Layout - packaging

Cabling

Fabrication and field access


Power – requirements – load

LocomotionMotion controller – 9WMotors -

ComputingMain – 20 W Planning – 30 W Core (PMAD and hibernation) – 5 W

CommunicationsEthernet - 6.3 WLow BW - ?

SensingNav pair – 3WSPI pair – 3WLocalization – FOG 3W, SBC 2.2WCrossbow Tilt sensor – 0.24W Pan/tilt – 18W (operating)Workspace cams – ?Sick laser – 17WNovatel GPS – 12W

ScienceChlorophyll - ?VisNIR – 50W ?Plowing - ?

life in the atacama, design review, december 19, 2003 carnegie mellon power system overview life in...

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