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## Ramana K.Vinjamuri 08/25/2004 Under direction of Dr. Pritpal Singh

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**Design and Implementation of a State-of-charge meter**for Lithium ion batteries to be used in Portable Defibrillators Ramana K.Vinjamuri 08/25/2004 Under direction of Dr. Pritpal Singh**Outline**• BACKGROUND • PROCEDURE (experimental setup) • MEASUREMENTS AND ANALYSIS • FUZZY LOGIC MODELING • IMPLEMENTATION IN MC68HC12 (micro controller) • CONCLUSIONS • FUTURE SCOPE**Portable defibrillators**Today portable defibrillators are considered as sophisticated devices by FDA (Food and Drug Administration). As a trend towards the widespread deployment of portable defibrillators in the hands of non-medical or non-technical personnel increases, there exists a need for a simple procedure to ensure that it will operate properly when needed.**Portable defibrillators**According to the FDA the major cause of defibrillator failure was improper care of the rechargeable battery . The effective operation of a portable defibrillator depends critically on the condition of the battery which are defined by State-of-Charge and State-of-Health.**Chemistry of Li ion batteries**Reactions that occur at Electrodes Positive LiMO2 → Li 1-xMO2 + x Li + + xe Negative C + x Li + +xe → Li x C Overall LiMO2 + C → Li x C + Li 1-x MO2**Features of Li-ion batteries**• Higher Energy density • Higher voltage • Long operating time • Compact**Definitions**SOC denotes the remaining pulses in a battery pack in one discharge cycle SOH represents the remaining number of cycles (charge-discharge) that can be obtained from a battery pack in its entire life. When the battery pack is new it is said to have 100% SOH. As the battery ages SOH eventually decreases.**Battery Interrogation Techniques**Efficient battery interrogation techniques are required for determining the state-of-charge (SOC) of a battery. The three basic methods are: 1) Coulomb counting 2) Voltage delay and 3) Impedance method**TYPICAL NYQUIST PLOT OF ELECTRO CHEMICAL CELL**Z’ Diffusion Anode Capacitive behavior Cathode 10 mHz 1kHz Rs 100Hz 0 inductive tail Z” Inductive behavior**Equivalent Circuit for this Cell**Rcathode Ranode RS L Canode Ccathode**Using AC impedance for determination of SOC**Research by J. P.Fellner At Air force laboratory, OH [1]**Using AC impedance for determination of SOC**Research by J. P.Fellner At Air force laboratory, OH [2]**Using AC impedance for determination of SOC**Research by Dr. Pritpal Singh [3]**Using AC impedance for determination of SOC**200 60 60 400 Research by J. P.Fellner At Air force laboratory, OH [2]**Introduction to Fuzzy Logic**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. The boundaries of the set are fuzzy rather than crisp. A fuzzy system is a rule-based mapping of inputs to outputs for a system.**Two approaches in Fuzzy Logic**• Mamdani Approach: Uses membership functions for both input and output variables • Sugeno Approach: Output membership functions are “singletons” (zero order) or polynomials (first order).**Example: Two input, two rule Fuzzy Model**n1 Rule1 m1 F1 S1 m2 Rule2 F2 n2 S2**Li-ion battery pack**• This Li ion battery pack consists of 12 cells connected in series parallel (4s3p configuration) • Effective voltage of the battery pack is 16.8 volts(4.2 volts per cell)**Chargeprofile**The profile that we have adopted is A constant current charging of 2.5 A till the battery voltage is 16.6172 v A constant voltage charging of 16.6 v till the charge current drops below 100mA**Discharge profile**The profile suggested by Medtronic/ Physio Control was Continuous discharge of 1.4 A and a discharge of 10 A for every 5 minutes for a period of 5 s**Dischargeprofile**Load current profile Voltage recovery profile**Apparatus**• For discharge -- Electronic load 6063B from Agilent Technologies • For the impedance and the voltage recovery measurements--Solartron 1280B,which is Potentiostat /Galvanostat /FRA • For charge --Centronix BMS2000, The Battery Management System • For different temperatures Tenney Environmental oven**Software**• To control the Electronic Load the software is HP VEE • To view and plot the impedance data its Zview and Zplot respectively • To view and plot the voltage recovery profiles data its Corr view and Corr ware**Test process**• Constant current discharge at 1.4A for 5 minutes, monitoring the voltage of the battery pack • Constant current discharge at 10 A for 5 seconds, monitoring the voltage of the battery pack • Repeat this process for a total of 1100 seconds which includes three 10 A discharges • EIS (Electro chemical Impedance spectroscopy) measurement over frequency range of 1Hz-1KHz • Repeat above four steps until end of discharge is reached (2.5V/cell)**Impedancemeasurements**Nyquist plot**Impedancemeasurements**Bode plots**Analysis**• Minimum voltage curves • Difference voltage curves**Minimum voltage curves**• The locus of the minimum voltages of every pulse in one cycle forms one curve corresponding to Cxx in the graph**Minimum voltage curves**• The locus of the minimum voltages of every pulse in one cycle forms one curve corresponding to Cxx in the graph • The above means the set of all As in figure shown**Difference voltage curves**• The locus of the difference between the maximum and minimum voltages of every pulse in a cycle forms a curve Cxx in the figure.**Difference voltage curves**• Voltage Difference=B-A • The locus of the difference between the maximum and minimum voltages of every pulse (B-A) in a cycle forms a curve Cxx in the figure.**FUZZY LOGIC MODELING**• Two models • To predict SOC –Remaining pulses (implemented) • To predict SOH –Cycle number (theoretical model)**Fuzzy Logic Modeling**• Inputs: Maximum voltage and Minimum voltage • Output: Pulses remaining • Type of mem. functions: Trapezoidal • Type of inference : Sugeno • No. of rules : 12 • 4 mem. Functions for Max. voltage • 3 mem. Functions for Min. voltage