Design Design andand Implementation of a Implementation of a State-of-charge meter State-of-charge meter for Lithium ion batteries to be for Lithium ion batteries to be

used in Portable Defibrillatorsused in Portable Defibrillators

Ramana K.VinjamuriRamana K.Vinjamuri

08/25/200408/25/2004

Under direction of Under direction of

Dr. Pritpal SinghDr. Pritpal Singh

OutlineOutline

BACKGROUNDBACKGROUND PROCEDURE (experimental setup)PROCEDURE (experimental setup) MEASUREMENTS AND ANALYSISMEASUREMENTS AND ANALYSIS FUZZY LOGIC MODELINGFUZZY LOGIC MODELING IMPLEMENTATION IN MC68HC12 (micro controller)IMPLEMENTATION IN MC68HC12 (micro controller) CONCLUSIONSCONCLUSIONS FUTURE SCOPEFUTURE SCOPE

BACKGROUNDBACKGROUND

Portable defibrillatorsPortable defibrillators

Today portable defibrillators are Today portable defibrillators are considered as sophisticated devices by considered as sophisticated devices by FDA (Food and Drug Administration). As a FDA (Food and Drug Administration). As a trend towards the widespread deployment trend towards the widespread deployment of portable defibrillators in the hands of of portable defibrillators in the hands of non-medical or non-technical personnel non-medical or non-technical personnel increases, there exists a need for a simple increases, there exists a need for a simple procedure to ensure that it will operate procedure to ensure that it will operate properly when needed.properly when needed.

Portable defibrillatorsPortable defibrillators

According to the FDA the major According to the FDA the major cause of defibrillator failure was cause of defibrillator failure was improper care of the rechargeable improper care of the rechargeable battery . The effective operation of a battery . The effective operation of a portable defibrillator depends portable defibrillator depends critically on the condition of the critically on the condition of the battery which are defined by State-battery which are defined by State-of-Charge and State-of-Health.of-Charge and State-of-Health.

Chemistry of Li ion batteriesChemistry of Li ion batteries

Reactions that occur at ElectrodesReactions that occur at Electrodes

Positive LiMO2 → Li Positive LiMO2 → Li 1-x1-xMO2 + x Li MO2 + x Li ++ + + xexe

Negative C + x Li Negative C + x Li ++ +xe → Li +xe → Li xx C C

Overall LiMO2 + C → Li Overall LiMO2 + C → Li xx C + Li C + Li 1-x1-x MO2MO2

Features of Li-ion batteries Features of Li-ion batteries

Higher Energy densityHigher Energy density Higher voltageHigher voltage Long operating timeLong operating time Compact Compact

DefinitionsDefinitions

SOC denotes the remaining pulses in a SOC denotes the remaining pulses in a battery pack in one discharge cycle battery pack in one discharge cycle

SOH represents the remaining number of SOH represents the remaining number of cycles (charge-discharge) that can be cycles (charge-discharge) that can be obtained from a battery pack in its obtained from a battery pack in its entire life. When the battery pack is new entire life. When the battery pack is new it is said to have 100% SOH. As the it is said to have 100% SOH. As the battery ages SOH eventually decreases. battery ages SOH eventually decreases.

Battery Interrogation TechniquesBattery Interrogation Techniques

Efficient battery interrogation Efficient battery interrogation techniques are required for techniques are required for determining the state-of-charge (SOC) determining the state-of-charge (SOC) of a battery.of a battery.

The three basic methods are:The three basic methods are:

1) Coulomb counting1) Coulomb counting

2) Voltage delay and 2) Voltage delay and

3) Impedance method3) Impedance method

Z’

Z”inductive tail

Rs

0

Diffusion

Anode

Cathode1kHz

100Hz

10 mHzCap

acit

ive

beha

vior

Indu

ctiv

e be

havi

orTYPICAL NYQUIST PLOT OF ELECTRO

CHEMICAL CELL

Equivalent Circuit for this CellEquivalent Circuit for this Cell

RS

RanodeRcathode

Canode Ccathode

L

Using AC impedance for Using AC impedance for

determination of SOCdetermination of SOC

Research by J. P.FellnerResearch by J. P.FellnerAt Air force laboratory, OH [1]At Air force laboratory, OH [1]

Using AC impedance for Using AC impedance for determination of SOCdetermination of SOC

Research by J. P.FellnerResearch by J. P.Fellner At Air force laboratory, OH [2]At Air force laboratory, OH [2]

Using AC impedance for Using AC impedance for determination of SOCdetermination of SOC

Research by Dr. Pritpal Singh [3]

Using AC impedance for Using AC impedance for determination of SOCdetermination of SOC

Research by J. P.FellnerResearch by J. P.Fellner At Air force laboratory, OH [2]At Air force laboratory, OH [2]

200

60

400

60

Introduction to Fuzzy LogicIntroduction to Fuzzy Logic

In fuzzy logic, a quantity may be a member In fuzzy logic, a quantity may be a member of a set to some degree or not be a member of a set to some degree or not be a member of a set to some degree. The boundaries of of a set to some degree. The boundaries of the set are fuzzy rather than crisp.the set are fuzzy rather than crisp.

A fuzzy system is a rule-based mapping of A fuzzy system is a rule-based mapping of inputs to outputs for a system.inputs to outputs for a system.

Two approaches in Fuzzy LogicTwo approaches in Fuzzy Logic

Mamdani Approach: Uses membership Mamdani Approach: Uses membership functions for both input and output functions for both input and output variablesvariables

Sugeno Approach: Sugeno Approach: Output Output membership functions are membership functions are “singletons” (zero order) or “singletons” (zero order) or polynomials (first order). polynomials (first order).

Example: Two input, two rule Fuzzy Model

m1

n1

F1

m2

n2 F2

S1

S2

Rule1

Rule2

Sugeno type of inferenceSugeno type of inference

PROCEDUREPROCEDURE

Li-ion battery packLi-ion battery pack

This Li ion battery pack consists of 12 This Li ion battery pack consists of 12 cells connected in series parallel cells connected in series parallel (4s3p configuration) (4s3p configuration)

Effective voltage of the battery pack Effective voltage of the battery pack is 16.8 volts(4.2 volts per cell)is 16.8 volts(4.2 volts per cell)

ChargeCharge profileprofile

The profile that we have adopted is The profile that we have adopted is

A constant current charging of 2.5 A A constant current charging of 2.5 A till the battery voltage is 16.6172 vtill the battery voltage is 16.6172 v

A constant voltage charging of 16.6 v A constant voltage charging of 16.6 v till the charge current drops below till the charge current drops below 100mA100mA

Discharge profileDischarge profile

The profile suggested by The profile suggested by

Medtronic/ Physio Control was Medtronic/ Physio Control was

Continuous discharge of 1.4 A and a Continuous discharge of 1.4 A and a discharge of 10 A for every 5 minutes discharge of 10 A for every 5 minutes for a period of 5 sfor a period of 5 s

DischargeDischarge profileprofile

Load current profile Voltage recovery profile

ApparatusApparatus

For discharge -- Electronic load 6063B from For discharge -- Electronic load 6063B from Agilent TechnologiesAgilent Technologies

For the impedance and the voltage recovery For the impedance and the voltage recovery measurements--Solartron 1280B,which is measurements--Solartron 1280B,which is Potentiostat /Galvanostat /FRAPotentiostat /Galvanostat /FRA

For charge --Centronix BMS2000, The Battery For charge --Centronix BMS2000, The Battery Management SystemManagement System

For different temperatures Tenney For different temperatures Tenney EnvironmentalEnvironmental oven oven

Battery pack, EC Load and Battery pack, EC Load and SolartronSolartron

EC-Load and OvenEC-Load and Oven

SoftwareSoftware

To control the Electronic Load the To control the Electronic Load the software is HP VEEsoftware is HP VEE

To view and plot the impedance data To view and plot the impedance data its Zview and Zplot respectivelyits Zview and Zplot respectively

To view and plot the voltage To view and plot the voltage recovery profiles data its Corr view recovery profiles data its Corr view and Corr wareand Corr ware

SoftwareSoftware controlcontrol

Test processTest process

Constant current discharge at 1.4A for 5 minutes, Constant current discharge at 1.4A for 5 minutes, monitoring the voltage of the battery pack monitoring the voltage of the battery pack

Constant current discharge at 10 A for 5 seconds, Constant current discharge at 10 A for 5 seconds, monitoring the voltage of the battery pack monitoring the voltage of the battery pack

Repeat this process for a total of 1100 seconds Repeat this process for a total of 1100 seconds which includes three 10 A dischargeswhich includes three 10 A discharges

EIS (Electro chemical Impedance spectroscopy) EIS (Electro chemical Impedance spectroscopy) measurement over frequency range of 1Hz-1KHzmeasurement over frequency range of 1Hz-1KHz

Repeat above four steps until end of discharge is Repeat above four steps until end of discharge is reached (2.5V/cell)reached (2.5V/cell)

Test processTest process

MEASUREMENTSMEASUREMENTS ANDAND ANALYSISANALYSIS

ImpedanceImpedance measurementsmeasurements

Nyquist plot

ImpedanceImpedance measurementsmeasurements

Bode plots

Monotonic variation of the voltage Monotonic variation of the voltage

recovery profilesrecovery profiles withwith SOCSOC

Comparing the First and the Last Comparing the First and the Last pulsepulse

AnalysisAnalysis

Minimum voltage curvesMinimum voltage curves Difference voltage curvesDifference voltage curves

Minimum voltage curvesMinimum voltage curves

The locus of the minimum voltages of The locus of the minimum voltages of every pulse in one cycle forms one every pulse in one cycle forms one curve corresponding to Cxx in the curve corresponding to Cxx in the graphgraph

One PulseOne Pulse

Minimum voltage curvesMinimum voltage curves

The locus of the minimum voltages of The locus of the minimum voltages of every pulse in one cycle forms one every pulse in one cycle forms one curve corresponding to Cxx in the curve corresponding to Cxx in the graphgraph

The above means the set of all As in The above means the set of all As in figure shownfigure shown

For battery pack at room For battery pack at room temperaturetemperature

Difference voltage curvesDifference voltage curves

The locus of the difference between The locus of the difference between the maximum and minimum voltages the maximum and minimum voltages of every pulse in a cycle forms a of every pulse in a cycle forms a curve Cxx in the figure.curve Cxx in the figure.

OneOne pulsepulse

Difference voltage curvesDifference voltage curves

Voltage Difference=B-AVoltage Difference=B-A The locus of the difference between The locus of the difference between

the maximum and minimum voltages the maximum and minimum voltages of every pulse (B-A) in a cycle forms of every pulse (B-A) in a cycle forms a curve Cxx in the figure.a curve Cxx in the figure.

For battery pack at room For battery pack at room temperaturetemperature

FUZZY LOGIC MODELINGFUZZY LOGIC MODELING

Two models1. To predict SOC –Remaining pulses (implemented)2. To predict SOH –Cycle number (theoretical model)

Fuzzy Logic ModelingFuzzy Logic Modeling

Inputs: Maximum voltage and Minimum Inputs: Maximum voltage and Minimum voltagevoltage

Output: Output: Pulses remainingPulses remaining Type of mem. functions: TrapezoidalType of mem. functions: Trapezoidal Type of inference : SugenoType of inference : Sugeno No. of rules : 12No. of rules : 12 4 mem. Functions for Max. voltage4 mem. Functions for Max. voltage 3 mem. Functions for Min. voltage3 mem. Functions for Min. voltage

Membership Functions for Membership Functions for Input1Input1

Membership Functions for Membership Functions for input2input2

Training error (0.95425)Training error (0.95425)

Testing error (0.99126)Testing error (0.99126)

Surface plotSurface plot

Fuzzy Logic ModelingFuzzy Logic Modeling

Inputs: Maximum voltage and Minimum Inputs: Maximum voltage and Minimum voltagevoltage

Output: Output: Cycle NumberCycle Number Type of mem. functions: TrapezoidalType of mem. functions: Trapezoidal Type of inference : SugenoType of inference : Sugeno No. of rules : 12No. of rules : 12 2 mem. Functions for Max. voltage2 mem. Functions for Max. voltage 6 mem. Functions for Min. voltage6 mem. Functions for Min. voltage

Testing error (2.6554)Testing error (2.6554)

Training error (2.565)Training error (2.565)

Surface plotSurface plot

IMPLEMENTATION IN MC68HC12 IMPLEMENTATION IN MC68HC12 (micro controller)(micro controller)

Implementation in Implementation in MC68HC12 (micro controller)MC68HC12 (micro controller)

Features of HC12:Features of HC12: On-Chip A/D conversion (any voltage On-Chip A/D conversion (any voltage

between 0-5 volts;0-00H and 5-FFH )between 0-5 volts;0-00H and 5-FFH ) Instruction Set with Fuzzy Logic Instruction Set with Fuzzy Logic

instructions (ability to implement instructions (ability to implement trapezoidal and triangular mem. trapezoidal and triangular mem. functions)functions)

Step down circuitStep down circuit

Voltage of the battery pack is stepped down Voltage of the battery pack is stepped down to be given as input to HC12to be given as input to HC12

R=511 K OhmsR=511 K Ohms

Op Amp=LMC60 42 AIN Op Amp=LMC60 42 AIN

Flow chart of the main programFlow chart of the main program

Timing DiagramTiming Diagram

Experimental setupExperimental setup

ResultsResultsDisplay showing 21 pulses remaining Average error=+/-2 pulses

LCD display Stem Plot

SummarySummary

Impedance and Voltage recovery profiles Impedance and Voltage recovery profiles collected for battery packs at room temperature collected for battery packs at room temperature and 0and 000CC

Battery characteristics were analyzed and Battery characteristics were analyzed and Minimum voltage curves and Difference voltage Minimum voltage curves and Difference voltage curves were developedcurves were developed

Based on the voltage recovery profiles a good Based on the voltage recovery profiles a good Fuzzy Logic Model was obtained to predict the Fuzzy Logic Model was obtained to predict the SOC of the battery pack at room temperature SOC of the battery pack at room temperature with a minimum error as low as 0.9with a minimum error as low as 0.9

Implemented on Micro Controller HC12 with a Implemented on Micro Controller HC12 with a very low error of +/-2 pulsesvery low error of +/-2 pulses

FutureFuture scopescope

This model can be extended to This model can be extended to estimate the SOC of the battery estimate the SOC of the battery packs at different temperaturespacks at different temperatures

An SOH meter that can predict the An SOH meter that can predict the cycle number can also be developed cycle number can also be developed provided, sufficient data is collected provided, sufficient data is collected for the battery packs at different for the battery packs at different temperaturestemperatures

PublicationsPublications1. 1. Pritpal Singh and Ramana Vinjamuri, Xiquan Wang and Pritpal Singh and Ramana Vinjamuri, Xiquan Wang and

David Reisner “David Reisner “FUZZY LOGIC MODELING OF EIS FUZZY LOGIC MODELING OF EIS MEASUREMENTS ON LITHIUM-ION BATTERIES”. MEASUREMENTS ON LITHIUM-ION BATTERIES”. EIS’04EIS’04

2. 2. Pritpal Singh and Ramana Vinjamuri, Xiquan Wang and Pritpal Singh and Ramana Vinjamuri, Xiquan Wang and

David Reisner.”David Reisner.” Analysis on Voltage recovery Analysis on Voltage recovery profiles and Impedance measurements of High profiles and Impedance measurements of High Power Li ion batteries”.Power Li ion batteries”.

41 st Power sources conference,2004 41 st Power sources conference,2004

ReferencesReferences

1.1. J.P.Fellner and R.A. Marsh “Use of the pulse current and AC J.P.Fellner and R.A. Marsh “Use of the pulse current and AC impedance characterization to enhance Lithium ion battery impedance characterization to enhance Lithium ion battery maintenance”, Electrochemical society proceedings volume 99-maintenance”, Electrochemical society proceedings volume 99-2525

2.2. J.P.Fellner, G.J.Loeber, S.S.Sadhu “Testing of lithium ion 18650 J.P.Fellner, G.J.Loeber, S.S.Sadhu “Testing of lithium ion 18650 cells and characterizing/predicting cell performance” Journal of cells and characterizing/predicting cell performance” Journal of Power sources conference 81-82(1999)Power sources conference 81-82(1999)

3.3. P. Singh, Y.S. Damodar, C. Fennie, and D.E. Reisner, “Fuzzy Logic-P. Singh, Y.S. Damodar, C. Fennie, and D.E. Reisner, “Fuzzy Logic-Based Determination of Lead Acid Battery State-of-Charge by Based Determination of Lead Acid Battery State-of-Charge by Impedance Interrogation Methods”Impedance Interrogation Methods”Procs. EVS-17Procs. EVS-17, Montreal, , Montreal,

Canada, Oct 15-18, 2000Canada, Oct 15-18, 2000