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

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)

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

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  1. 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

  2. Outline • BACKGROUND • PROCEDURE (experimental setup) • MEASUREMENTS AND ANALYSIS • FUZZY LOGIC MODELING • IMPLEMENTATION IN MC68HC12 (micro controller) • CONCLUSIONS • FUTURE SCOPE

  3. BACKGROUND

  4. 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.

  5. 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.

  6. 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

  7. Features of Li-ion batteries • Higher Energy density • Higher voltage • Long operating time • Compact

  8. 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.

  9. 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

  10. TYPICAL NYQUIST PLOT OF ELECTRO CHEMICAL CELL Z’ Diffusion Anode Capacitive behavior Cathode 10 mHz 1kHz Rs 100Hz 0 inductive tail Z” Inductive behavior

  11. Equivalent Circuit for this Cell Rcathode Ranode RS L Canode Ccathode

  12. Using AC impedance for determination of SOC Research by J. P.Fellner At Air force laboratory, OH [1]

  13. Using AC impedance for determination of SOC Research by J. P.Fellner At Air force laboratory, OH [2]

  14. Using AC impedance for determination of SOC Research by Dr. Pritpal Singh [3]

  15. Using AC impedance for determination of SOC 200 60 60 400 Research by J. P.Fellner At Air force laboratory, OH [2]

  16. 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.

  17. 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).

  18. Example: Two input, two rule Fuzzy Model n1 Rule1 m1 F1 S1 m2 Rule2 F2 n2 S2

  19. Sugeno type of inference

  20. PROCEDURE

  21. 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)

  22. 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

  23. 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

  24. Dischargeprofile Load current profile Voltage recovery profile

  25. 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

  26. Battery pack, EC Load and Solartron

  27. EC-Load and Oven

  28. 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

  29. Softwarecontrol

  30. 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)

  31. Test process

  32. MEASUREMENTSANDANALYSIS

  33. Impedancemeasurements Nyquist plot

  34. Impedancemeasurements Bode plots

  35. Monotonic variation of the voltage recovery profileswithSOC

  36. Comparing the First and the Last pulse

  37. Analysis • Minimum voltage curves • Difference voltage curves

  38. Minimum voltage curves • The locus of the minimum voltages of every pulse in one cycle forms one curve corresponding to Cxx in the graph

  39. One Pulse

  40. 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

  41. For battery pack at room temperature

  42. 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.

  43. Onepulse

  44. 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.

  45. For battery pack at room temperature

  46. FUZZY LOGIC MODELING • Two models • To predict SOC –Remaining pulses (implemented) • To predict SOH –Cycle number (theoretical model)

  47. 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

  48. Membership Functions for Input1

  49. Membership Functions for input2

  50. Training error (0.95425)

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