Battery Control Boards for Li-Ion Batteries on Mars ... · Battery Control Boards for Li-Ion...

Mars Exploration Rover

Jet Propulsion LaboratoryCalifornia Institute of Technology

NASA Battery Workshop Huntsville, AL, November 16-19, 2004

Battery Control Boards for Li-Ion Batteries on Mars Exploration Rovers

R. Ewell, B. V. Ratnakumar, M. Smart, K. B Chin,L. Whitcanack, S. R. Narayanan and S. Surampudi

https://ntrs.nasa.gov/search.jsp?R=20080015793 2018-07-19T10:33:54+00:00Z


Payload• Panoramic Camera • Miniature Thermal Emission

Spectrometer (Mini-TES)• Mössbauer Spectrometer • Alpha Particle X-Ray

Spectrometer (APXS)• Magnets• Microscopic Imager (MI)• Rock Abrasion Tool (RAT)

To Date• About 290 sols

completed• Evidence of past water

MARS EXPLORATION ROVER


Avionics• Rad6000 Flight Computer (20Mhz,

128MB DRAM)• 256MB Non-volatile FLASH data

storage• Analog, digital, serial IO• Motor control for 36 brushed motors, 4

stepper motors & 4 brushless motorsPower• Triple-Junction GaInP/GaAs/Ge cell

deployable solar arrays• (2) 8A-hr Li-Ion rechargeable batteries• Power conversion and distributionNavigation Sensors• Mast mounted stereo navigation

cameras - NAVCAMs - Front & Rear stereo hazard cameras - HAZCAMs -with 120deg FOV) SUNCAM (mounted on HGA gimbal)

• 6DOF IMU

Telecom• Direct to Earth Communication (X-

band) with fixed Low Gain and gimbaled High Gain Antennas

• Orbiter relay communication (UHF) with fixed monopole antenna

Mobility System• 6 wheel Rocker-Bogie mechanism with

25cm diameter wheels• 5cm/s top speed (~0.6m/minute under

autonomous navigation)Thermal• Aerogel insulated Warm Electronics

Box• Resistive heaters on external

motors/cameras and internal components

• Radioisotope heating units (RHUs)• Battery thermal switch heat rejection

system• SSPA Loop Heat Pipe heat rejection

system

ROVER CAPABILITIES


• First rover with a rechargeable battery, Lithium-ion.• About ten times as big as the Sojourner Rover on Mars Pathfinder

mission (1995 with a primary Li-SOCl2 battery)

MER Rovers & Sojourner Spare Rovers


Rover Battery Assembly Unit

• Two parallel batteries each with eight (10 Ah) cells in series - 30 V, 16 Ah (480 Wh).

• Fabricated by Yardney Technical Products, CT (Lithion)

Advanced Li-ion battery for MER

MER Cell (8 Ah)

MER Li Ion Cell(10 Ah).

• Low Temperature Electrolyte Development: At JPL under Mars Exploration Program (92-96)

• Cell Development: AFRL, NASA GRC, JPL, RDECOM, with Yardney Technical Products and SAFT: (97-01)

• Performance Database Dev. : JPL, NASA-GRC (97-03)

• Flight Hardware Design & Fabrication: JPL, Yardney (01-03)

• Battery Operational Strategies: JPL (02-04)

Mars Exploration RoverNeed for Cell Balance on Charge

• Li-ion cells diverge, both during cycling and storage even after a thorough matching initially.– Moderate cycle life requirement (500 cycles).– About three years of calendar life; Seven months of cruise.– Low temperature operation.

• Low energy margins and deep DODs (40-50%).• Overcharge of Li-ion cell results in performance degradation and/or safety

event– Oxidative (or even reductive degradation of electrolyte; Structural instability of

cathode and lithium plating at anode.• Over-discharge results in copper dissolution.• Individual cell monitor and control essential

Mars Exploration RoverCell Divergence on Cycling

3.20

3.25

3.30

3.35

3.40

3.45

3.50

0 1000 2000 3000 4000 5000 6000

Cycle Number

Bat

tery

Vol

tage

(V)

Aux # 1Aux # 2Aux # 3Aux # 4Aux # 5Aux # 6Aux # 7Aux # 8

40 % DOD LEO CyclingCharge Current = 12.5 A (0.5 C Rate)

Charge Voltage = 30.40 V (55 minutes)Discharge Current = 17.5 A (0.7 C Rate)

Discharge Time = 35 minutesMSP01 Lander Li-Ion Battery (25 Ah, 8-Cell)Lithion, Inc. (Yardney)

40 % DOD LEO Cycling of 30 V- 25 Ah Li-ion Battery at 23oCCell End-of-Discharge (EOD) Voltages

Chamber TemperatureController Error (3 to 10oC)

Loose External Cell Connetion

(Cell # 3)


Rover SolarArray

Cruise Shunt LimiterAssembly(5 Stages)

CruiseShunt

Radiator1/2 Panel

CruisePower

DistributionUnits (2)

LOADS

CRUISESTAGE

Rover Shunt LimiterUnit

(2 Stages)

Rover SolarArray

Rover SolarArray

Rover SolarArray

Rover SolarArray Panel (x6)

RoverPower

DistributionUnit

LOADSRoverBatteryControlBoard

RoverPower

ConverterUnit

VME Loads

IMU, Cameras,Motor Logic

LanderPowerControl

Unit

Lander PyroSwitchingAssembly

LanderPower

DistributionUnit

ROVERSTAGE

LANDERSTAGE

LOADS

BACKSHELLSTAGE

LiSo2Batteries

(x5)

Li-IonBatteries

(x2)

RoverShunt

Radiator

Umbilical to LCE

T

(x5)

(x2)

T

Lander PyroSwitchingInterface

Cruise Solar Array (4 Panels)

1/2 Panel

Cruise PowerConverter

Unit

Pyro Bus A

Pyro Bus B

RADAR ALTIMETER

Rover PyroSwitchingAssembly

ThermalBattery

(x2)

Backshell PyroSwitchingAssembly

LANDER PYRO LOADS

BACkSHELL PYROLOADS

ROVER PYRO LOADS

CRUISE PYRO LOADS

Vc

BIMU PCU

LightningSuppression

Assemblies 1 & 2

dgn- 10/28/02

(Bridle)

Field Joint& Filter

Assembly

(AVIONICS CARDS)

(AVIONICS CARD)

MER Power S/S Functional Block Diagram


BCB Purpose relative to Li-ion Batteries.

• Autonomously control Li-ion Battery, continuously even when flight computer is not operating.

• Provides over-charge and over-discharge protection.• Ensures all Li-ion cells are maintained with a maximum cell

spread of 120 millivolts, assuming that the battery is fully charged periodically.

• Provides battery temperature control.• Provides continuous battery telemetry and amp-hr integration.• Fully functionally redundant


BCB: Description

• Autonomously provides battery cell balancing to achieve maximum battery energy capacity.

• Switches on warm-up and survival heaters for the Rover batteries.– Heaters are thermostatically controlled.

• Isolates the Rover batteries from the power bus by use of relays.– For the main purpose of disconnecting the batteries from the bus during ATLO

when the S/C is un-powered.• Disconnects the Rover batteries from the power bus under cell over-voltage

and cell under-voltage conditions by use of power FETS.• Generates the wake-up signal to the RPDU to switch ON the VME.

– Is based on either GSE wake-up, solar array current or wake-up timer.– Keeps the switch on for 240 seconds to allow the VME to boot up. The switch

gets reasserted when the FSW is up and running properly.• The BCB also has the capability of switching the VME OFF.

– This is to ensure that if the VME does not properly boot up, the BCB can switch the VME off for 30 seconds and switch the VME back on again.


Cell 1

Cell 8

ANAL

OG

CIR

CU

ITS

FPGA(Side

1)

Umbilicalto GSE

Serial I/F toTelecom

(TSB)

Power Bus

Rs

T

Battery 1IsolationRelays

HousekeepingPCU

Wake/Up, etc.Circuits

VMEON

VMEOFF

I/OInterface

Serial I/F toTelecom

(TSB)

Umbilicalto GSE

Power BusReturn

FPGA(Side

2)

HousekeepingPCU

Over-chargedisable

Over-dischargedisable

B

A

C

B C

APyro Bus A(RPSA)

Cell 1

Cell 8

ANALO

G C

IRC

UITS

Rs

T

Battery 2IsolationRelays

Over-chargedisable

Over-dischargedisable

B

A

C

BC

A Pyro B Bus(RPSA)

Mission Clock(TSB)

RSLUGnd Tree

RSLUAnalog

RSLUAnalog

BCB: Block Diagram


BCB: Telemetry

• Monitors all of the critical power analog telemetry signals in the Rover.– Rover solar array Voc and solar array Isc– Bus voltage– Rover solar array current– Rover shunt current– Lander bus current (bi-directional)– Cruise bus current (bi-directional)– RPDU current– Rover battery voltages – Rover battery cell voltages (8 per battery)– Rover battery currents (1 per battery)– Rover battery temperatures (5)

• 3 internal, 1 battery case temperature, and routes 1 through umbilical.

– Measures & stores critical night time measurements for thermal


BCB: Battery Control

• We have 1 BCB for each battery. Each operates independently.• Over-discharge protection: Opens the discharge FET if any cell

voltage < 2.9 V for 3 samples of 1 second• Overcharge protection: Opens the charge FET if any cell > 4.15 V,

or if all cells above 4.12 V, or if any cell is below 1V while any other cell is > 2.9 V. (Cell short protection)

• Cell Balancing: Puts a resistor in parallel with cells that go above 4.12 V.

• BCB History: Each BCB stores all the analog measurements in a buffer every 10 minutes, whether the VME is on or not, up to 31 2/3 hours. We have reset the BCBs 5 minutes apart, so that most channels are sampled at 5 minute increments. By command, FSW can generate a data product that has user-selectable channels over a user-selectable duration.

• Battery Isolation Relays: Used only in the case of a battery failure.


BCB: Cell Balancing

• Spacecraft has 8 hardware selectable levels of bus voltage control– Maximum bus voltage maintained by active shunt– Minimum bus voltage maintained by having Li-Ion batteries on bus

• Each side of BCB has 4 firmware selectable levels of cell charge control:– Vcmd: command value, if any cell voltage exceeds this value, battery is taken

off of bus relative to charge by a FET– Vbp: bypass value, if any cell voltage exceeds this value, a shunt resistor is put

in parallel with the cell as a partial shunt– Vebp: end bypass value, if the voltage of any cell that was in bypass falls

below this value it will be taken out of bypass– Vch: charge value, when every cell voltage drops below this value, battery will

be put back on bus relative to charge• In addition each BCB has two firmware set values relative to discharge:

– Vd: discharge value, ensure battery is on bus relative to discharge when every cell voltage is above this value

– Vsd: stop discharge value, take battery off bus relative to discharge when any cell falls below this value


VoltageVcmd(FSW)

Actual Vcmd Voltage

V(bypass)Vbp =

Vcmd - 30mv

V(end bypass)Vebp = Vcmd -

70mv

V(charge)Vch = Vcmd -

150mv

V(discharge)Vd = 3.4

V(stop)discharge

Vsd = 2.9v

4.2 4.199 4.169 4.128 4.049 3.4 2.9

4.1 4.149 4.119 4.080 3.999 3.4 2.9

4.0 3.949 3.919 3.878 3.799 3.4 2.9

3.9 3.849 3.820 3.779 3.699 3.4 2.9

BCB: Cell Balancing Parameters


Vcmd -- 4.15 V

Vbp -- 4.12 V

Vch -- 4.00 V

Vebp -- 4.08 V

Vbus -- 32.8 V (4.10 V/cell)Equiv Cell Voltage

4.15 V

4.10 V

4.05 V

4.00 V

BCB: Typical Cell Balancing Parameters


• Terminology Definitions– Vcmd = (Vcommand)= Vsc (Vstop

charge) = one of four prog levels (3.85, 3.95, 4.15, 4.20V)

– Vbp (Vbypass) = Vcmd - 30mV– Vebp (Vend bypass) = Vcmd -

70mV– Vch (Vcharge) = Vcmd -

150mV– Vd (Vdischarge) = 3.4V– Vsd (Vstop discharge) = 2.9V

• Charge control– Stop Charge (open charge FET) if:

• Any cell is greater than or equal to Vcmd

• All cells are above Vbp

• Any cell is <1V and the battery is >20V.

– Start Charge (close charge FET) if:• All cells are below Vch

• After POR– Stop Discharge (open discharge FET) if:

• Any cell is less than or equal to Vsd– Start Discharge (close discharge FET) if:

• All cells are above Vd.• Charge Balancing

– Start cell bypassing at or above Vbp– Stop cell bypassing at or below Vebp

Battery Management Protocol


BCB Flight Board (Front)


BCB Flight Board (Back)

Mars Exploration RoverSPIRIT Cruise Battery 2 Cell Voltages

4.05

4.07

4.09

4.11

4.13

4.15

18:00 20:00 22:00 0:00 2:00 4:00 6:00 8:00

Time, hours

Cel

l Vol

tage

s, V

olts

B2_bat_cell1 B2_bat_cell2

B2_bat_cell3 B2_bat_cell4B2_bat_cell5 B2_bat_cell6


MER In-Flight Cell Balancing


Spirit Cruise Battery 2 Cell Bypass State

0

2

18:00 20:00 22:00 0:00 2:00 4:00 6:00 8:00

Time, hours

Cel

l Byp

ass

Sta

te

B2_CELL_1_BP B2_CELL_2_BPB2_CELL_3_BP B2_CELL_4_BPB2_CELL_5_BP B2_CELL_6_BPB2_CELL_7_BP B2_CELL_8_BP

MER In-Flight Cell Balancing


3.6

3.7

3.8

3.9

4

4.1

4.2

5/19/0300:00

6/8/03 00:00 6/28/0300:00

7/18/0300:00

8/7/03 00:00 8/27/0300:00

9/16/0300:00

10/6/0300:00

10/26/0300:00

11/15/0300:00

12/5/0300:00

12/25/0300:00

1/14/0400:00

Data & Time

Cel

l Vol

tage

s

Cell1

Cell2

Cell3

Cell4

Cell5

Cell6

Cell7

Cell8

Battery 1

• ~ 25% discharge during launch. 80% SOC during cruise and fully charged before landing.• Cells periodically balanced via bypass, if the cell divergence is sufficiently large.

Launch

Spirit Li Ion Batteries on Cruise


3.6

3.7

3.8

3.9

4

4.1

4.2

5/19/0300:00

6/8/03 00:00 6/28/0300:00

7/18/0300:00

8/7/03 00:00 8/27/0300:00

9/16/0300:00

10/6/0300:00

10/26/0300:00

11/15/0300:00

12/5/0300:00

12/25/0300:00

1/14/0400:00

Data & Time

Cel

l Vol

tage

s

Cell1

Cell2

Cell3

Cell4

Cell5

Cell6

Cell7

Cell8

BATTERY 2

• Behavior of battery 2 is similar to battery 1

Spirit Li Ion Batteries on Cruise

• Similar behavior on Opportunity as well.


Spirit Li Ion Batteries Thro’ Sol 74

• End of discharge voltages are 29-30 V.• Both batteries have nearly identical voltages

Battery Voltages on Spirit

24

26

28

30

32

34

0 10 20 30 40 50 60 70 80

Sol

Bat

tery

Vol

tage

, V

bat_A_vbat_B_v


Spirit Li Ion Batteries Thro’ Sol 74

• Typical minimum cell voltage : 3.6 V (~ 50%DOD)• Spirit anomaly attributed to flash memory, which was later erased. • Batteries experienced a fairly deep discharge and yet recovered well.

Cell Voltages on Spirit- Bat A

3.0

3.2

3.4

3.6

3.8

4.0

4.2

0 10 20 30 40 50 60 70 80Sol

Bat

tery

Vol

tage

, V






Opportunity Li Ion Batteries Thro’ Sol 54

• Battery End of discharge voltage: 28 V; A little bit lower than in the case of Spirit.

• Both batteries have nearly identical voltages.

Battery Voltages on Opportunity

24

26

28

30

32

34

0 5 10 15 20 25 30 35 40 45 50 55

Sol

Bat

tery

Vol

tage

, V

bat_A_v bat_B_v


Opportunity Li Ion Batteries Thro’ Sol 54

• Minimum cell voltage : 3.55 V, about 50 mV lower than on Spirit

Cell Voltages in Battery 1 on Opportunity

3

3.2

3.4

3.6

3.8

4

4.2

4.4

0 5 10 15 20 25 30 35 40 45 50 55

Sol

Bat

tery

Vol

tage

, V

B1_bat_cell1 B1_bat_cell2 B1_bat_cell3

B1_bat_cell4 B1_bat_cell5 B1_bat_cell6



Charge Discharge Capacity on Spirirt & Opportunity

-15

-12

-9

-6

-3

0

3

6

9

12

15

0 20 40 60 80 100

Sol

Cap

acity

, Ah

Spirit-Dis

Spirit-Charge

Opportunity-Dis

Opportunity-Ch

• Max discharge current is 1.6 A and the typical charge current is ~1 A.• Depth of discharge is typically 60-70%. • C/D ratio is close to one.• Higher DOD on Opportunity, compared to Spirit

Charge and Discharge Capacity


Cell Divergence on Opportunity

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 10 20 30 40 50 60 70 80

SolM

ax. C

ell D

iver

genc

e, V

Opportunity-Bat 2

Opportunity-Bat 1

• Cell divergence increases upon cycling, almost to the extent as on Spirit.

Cell Divergence on Spirirt

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 20 40 60 80 100Sol

Max

Cel

l Div

erge

nce,

V

Spirit-Bat 1

Spirit-Bat 2

Cell Divergence in Rover Batteries


• Battery temperatures are ranging from + 5 to 22oC.

• Battery temperatures are about 1-2oC lower than on the Spirit, but about 10oC warmer than anticipated.

Battery Temperatures on Spirit

-5

0

5

10

15

20

25

0 10 20 30 40 50 60 70 80

Sol

Bat

tery

Tem

pera

ture

,o C

temp_mid

Battery Temperatures on Opportunity

-5

0

5

10

15

20

25

0 6 12 18 24 30 36 42 48 54 60

Sol

Bat

tery

Tem

pera

ture

, o C

temp_mid

Rover Battery Temperatures


24

27

29

32

34

1 21 41 61 81 101 121 141 161 181Mars Sols

Vol

tage

Max Bus Voltage

Min Bus Voltage

MER Spirit Battery Update


24

26

28

30

32

34

0 20 40 60 80 100 120 140 160 180Sols

Vol

tage

, V

Min Bus Voltage

Max Bus Voltage

MER Opportunity Battery Update


MER Battery Ground Test Predicts

RBAU Impedance with Temperature

0

200

400

600

800

1000

1200

1400

-40 -30 -20 -10 0 10 20 30 40Temp, oC

Impe

danc

e, m

Ohm

s

FM4A-Initial

FM4A-90 sols

FM4B-Initial

FM4B-90 sols

Values at -25 and -30oC are based on prediction

Fig. 11 Li-Ion battery impedance from ground tests

Rover Battery Capacity vs Temperature

0

2

4

6

8

10

12

-40 -30 -20 -10 0 10 20 30 40Temp, oC

Bat

tery

Cap

acity

, Ah

FM4A-Initial

FM4A-90 sols

FM4B-Initial

FM4B-90 sols

Values at -25 and -30oC are based on prediction

Fig. 12 Li-Ion battery impedance from ground tests


Summary

• Rechargeable Lithium-ion batteries have been operating successfully on both Spirit and Opportunity rovers for the last two years, which includes six months of Assembly Launch and Test Operations (ATLO), seven months of cruise and about eleven months of surface operations.

• The Battery Control Boards designed and fabricated in-house would protect cells against overcharge and over-discharge and provide cell balance. Their performance has thus far been quite satisfactory.

• The ground data o the mission simulation battery project littlecapacity loss of less than 3% during cruise and 180 sols.

• Batteries are poised to extend the mission beyond six months, if not a couple of years.


Acknowledgments

• The work described here was carried out at the Jet Propulsion Laboratory (JPL), California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) and was supported by NASA Mars Exploration Rover Project.

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