Battery Management Systems
`Design by Modelling
`
`H.J. Bergveld
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`The work described in this thesis has been carried out at Philips Research
`Laboratories Eindhoven as part of the Philips Research programme.
`
`Cover design: Hennie Alblas
`Figures: Hennie Alblas
`Printed by: University Press Facilities, Eindhoven
`
`Explanation of the cover
`The cover shows a transparent battery as an illustration of the use of battery models
`for the design of Battery Management Systems.
`
`© Royal Philips Electronics N.V. 2001
`All rights reserved. No part of this publication may be reproduced, stored in a
`retrieval system, or transmitted, in any form or by any means, electronic,
`mechanical, photocopying, recording, or otherwise, without the prior written consent
`of the copyright owner.
`
`CIP-Gegevens Koninklijke Bibliotheek, Den Haag
`Bergveld, Hendrik Johannes
`Battery Management Systems-Design by Modelling
`Proefschrift Universiteit Twente, Enschede, – Met lit. opg., - Met samenvatting in
`het Nederlands
`ISBN 90-74445-51-9
`Trefw.: Batteries, Secondary Cells, Power Supplies to Apparatus, Modelling,
`Battery Management, NiCd, Li-ion, Power Amplifiers, Cellular Phones
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`BATTERY MANAGEMENT SYSTEMS
`DESIGN BY MODELLING
`
`PROEFSCHRIFT
`
`ter verkrijging van
`de graad van doctor aan de Universiteit Twente,
`op gezag van de rector magnificus,
`prof.dr. F.A. van Vught,
`volgens besluit van het College voor Promoties
`in het openbaar te verdedigen
`op donderdag 28 juni 2001 te 16.45 uur.
`
`door
`
`Hendrik Johannes Bergveld
`
`geboren op 17 maart 1970
`te Enschede
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`Dit proefschrift is goedgekeurd door de promotoren:
`Prof.dr.ir. P.P.L. Regtien (Universiteit Twente)
`Prof.dr. P.H.L. Notten
`(Technische Universiteit Eindhoven, Philips Research
`Laboratories, Eindhoven)
`
`Samenstelling promotiecommissie:
`Prof.dr. H. Wallinga
`Voorzitter
`Prof.dr. J.M. Tarascon
`Université de Picardie Jules Verne, Amiens, Frankrijk
`Dr.ir. M.J.M. Pelgrom
`Philips Research Laboratories, Eindhoven
`Prof.dr.ir. P. Bergveld
`Universiteit Twente
`Prof.dr. J.F.J. Engbersen Universiteit Twente
`Prof.dr.ir. B. Nauta
`Universiteit Twente
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`Ter nagedachtenis aan mijn broer
`To the memory of my brother
`
`BONIFACIO MARINUS BERGVELD
`
` 20 August 1973 30 January 1995
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`Simple example of Battery Management
`(by Franquin © MARSU, 2001, printed with permission, see www.gastonlagaffe.com)
`
`Aan Peggy en mijn ouders
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`Table of contents
`
`List of abbreviations
`
`List of symbols
`
`1. Introduction
`
`1.1 The energy chain
`1.2 Definition of a Battery Management System
`1.3 Motivation of the research described in this thesis
`1.4 Scope of this thesis
`1.5 References
`
`2. Battery Management Systems
`
`2.1 A general Battery Management System
`2.2 Battery Management System parts
`2.2.1 The Power Module (PM)
`2.2.2 The battery
`2.2.3 The DC/DC converter
`2.2.4 The load
`2.2.5 The communication channel
`2.3 Examples of Battery Management Systems
`2.3.1
`Introduction
`2.3.2 Comparison of BMS in a low-end and
`high-end shaver
`2.3.3 Comparison of BMS in two types of cellular
`phones
`2.4 References
`
`3. Basic information on batteries
`
`3.1 Historical overview
`3.2 Battery systems
`3.2.1 Definitions
`3.2.2 Battery design
`3.2.3 Battery characteristics
`3.3 General operational mechanism of batteries
`3.3.1
`Introduction
`3.3.2 Basic thermodynamics
`3.3.3 Kinetic and diffusion overpotentials
`3.3.4 Double-layer capacitance
`
`i
`
`vii
`
`ix
`
`1
`
`1
`3
`4
`5
`6
`
`9
`
`9
`10
`10
`14
`18
`19
`19
`22
`22
`
`22
`
`25
`29
`
`31
`
`31
`33
`33
`35
`36
`43
`43
`44
`45
`50
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`ii
`
`3.3.5 Battery voltage
`3.4 References
`
`4. Battery modelling
`
`52
`52
`
`55
`
`4.1 General approach to modelling batteries
`55
`4.1.1 Chemical and electrochemical potential
`58
`4.1.2 Modelling chemical and electrochemical reactions 59
`4.1.3 Modelling mass transport
`67
`4.1.4 Modelling thermal behaviour
`82
`4.2 A simulation model of a rechargeable NiCd battery
`86
`4.2.1
`Introduction
`86
`4.2.2 The nickel reaction
`89
`4.2.3 The cadmium reactions
`92
`4.2.4 The oxygen reactions
`97
`4.2.5 Temperature dependence of the reactions
`102
`4.2.6 The model
`103
`4.3 A simulation model of a rechargeable Li-ion battery
`107
`4.3.1
`Introduction
`107
`4.3.2 The LiCoO2 electrode reaction
`108
`4.3.3 The LiC6 electrode reaction
`113
`4.3.4 The electrolyte solution
`117
`4.3.5 Temperature dependence of the reactions
`118
`4.3.6 The model
`118
`4.4 Parameterization of the NiCd battery model
`124
`4.4.1
`Introduction
`124
`4.4.2 Mathematical parameter optimization
`126
`4.4.3 Results and discussion
`131
`4.4.4 Quality of the parameter set presented in section
`4.4.3 under different charging conditions
`4.4.5 Results obtained with a modified NiCd battery
`model and discussion
`4.5 Simulation examples
`4.5.1 Simulations using the NiCd model presented in
`section 4.2
`4.5.2 Simulations using the Li-ion model presented in
`section 4.3
`4.6 Conclusions
`4.7 References
`
`155
`162
`165
`
`5. Battery charging algorithms
`
`5.1 Charging algorithms for NiCd and NiMH batteries
`5.1.1 Charging modes, end-of-charge triggers and
`charger features
`
`169
`
`169
`
`169
`
`138
`
`144
`149
`
`149
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`
`5.1.2 Differences between charging algorithms
`for NiCd and NiMH batteries
`5.1.3 Simulation example: an alternative charging
`algorithm for NiCd batteries
`5.2 Charging algorithm for Li-ion batteries
`5.2.1 The basic principle
`5.2.2 The influence of charge voltage on the
`charging process
`5.2.3 The influence of charge current on the
`charging process
`5.2.4 Simulation example: fast charging of a
`Li-ion battery
`5.3 Conclusions
`5.4 References
`
`6. Battery State-of-Charge indication
`
`175
`
`177
`184
`184
`
`186
`
`187
`
`188
`191
`192
`
`193
`
`6.1 Possible State-of-Charge indication methods
`193
`6.1.1 Definitions
`193
`6.1.2 Direct measurements
`195
`6.1.3 Book-keeping systems
`199
`6.1.4 Adaptive systems
`202
`6.1.5 Some remarks on accuracy and reliability
`203
`6.2 Experimental tests using the bq2050
`204
`6.2.1 Operation of the bq2050
`204
`6.2.2 Set-up of the experiments
`206
`6.2.3 Results and discussion
`208
`6.2.4 Conclusions of the experiments
`211
`6.3 Direct measurements for Li-ion batteries: the EMF method 212
`6.3.1
`Introduction
`212
`6.3.2 EMF measurement methods
`212
`6.3.3 Measured and simulated EMF curves for the
`214
`CGR17500 Li-ion battery
`6.3.4 Conclusions
`219
`6.4 A simple mathematical model for overpotential description 219
`6.5 Proposed set-up for State-of-Charge system
`225
`6.5.1 The algorithm
`225
`6.5.2 Comparison with the bq2050 system
`229
`6.5.3 Comparison with systems found in the literature
`230
`6.6 Experimental tests with the system proposed in section 6.5 231
`6.6.1
`Introduction
`231
`6.6.2 Set-up of the experiments
`231
`6.6.3 Experimental results
`232
`6.6.4 Discussion of the results
`235
`6.6.5 Conclusions of the experiments
`237
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`
`6.7 Conclusions
`6.8 References
`
`238
`239
`
`7. Optimum supply strategies for Power Amplifiers
`in cellular phones
`241
`
`241
`245
`246
`250
`251
`252
`253
`255
`
`7.1 Trends in cellular systems
`7.2 The efficiency control concept
`7.2.1 Basic information on Power Amplifiers
`7.2.2 Optimum supply voltage for optimum efficiency
`7.3 DC/DC conversion principles
`7.3.1 Linear voltage regulators
`7.3.2 Capacitive voltage converters
`7.3.3
`Inductive voltage converters
`7.3.4 EMI problems involved in capacitive and
`258
`inductive voltage converters
`7.3.5
`Inductive voltage conversion for efficiency control 258
`7.4 Simulation model derivation
`258
`7.4.1 DC/DC down-converter
`258
`7.4.2 Power Amplifier
`260
`7.5 Theoretical benefits of efficiency control
`261
`7.5.1 Simulation set-up
`262
`7.5.2 Results and discussion
`263
`7.5.3 Conclusions
`265
`7.6 Experimental results obtained with a CDMA PA
`266
`7.6.1 Measurement set-up
`266
`7.6.2 Measurement results and discussion of part 1:
`no DC/DC converter
`7.6.3 Measurement results and discussion of part 2:
`with DC/DC converter
`7.6.4 Estimation of talk time increase in a
`271
`complete CDMA cellular phone
`7.7 Application of efficiency control in a GSM cellular phone 274
`7.7.1 GSM power control protocol
`274
`7.7.2 Modifications in the Spark GSM phone
`276
`7.7.3 Measurement results and discussion
`279
`7.7.4 Conclusions of the experiments
`281
`7.8 Conclusions
`281
`7.9 References
`282
`
`267
`
`269
`
`8. General conclusions and recommendations
`
`8.1 General conclusions
`8.2 Recommendations
`8.3 References
`
`285
`
`285
`287
`289
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` v
`
`List of publications and patents
`
`Summary
`
`Samenvatting
`
`Dankwoord
`
`Curriculum Vitae (English)
`
`Curriculum Vitae (Nederlands)
`
`291
`
`293
`
`297
`
`303
`
`305
`
`306
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`vi
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`List of abbreviations
`
`vii
`
`ACPI
`ACPR
`ADC
`AM
`BER
`BIOS
`BMS
`CAC
`CC
`CDMA
`Cd(OH)2
`CHC
`CV
`DAC
`DCR
`DCS
`DMC
`DQPSK
`DSP
`DTC
`e
`EC
`ECC
`EDGE
`EM
`EMC
`EMF
`EMI
`ESR
`FDD
`FDMA
`FM
`FSK
`GMSK
`GSM
`H+
`H2O
`H2SO4
`HVIC
`ID
`IEC
`IIC
`KOH
`LED
`LCD
`LR
`Li-ion
`LiCoO2
`
`Advanced Configuration and Power Interface
`Adjacent Channel Power Ratio
`Analogue-to-Digital Converter
`Amplitude Modulation
`Bit Error Rate
`Basic Input Output System
`Battery Management System
`Compensated Available Charge
`Constant Current
`Code-Division Multiple Access
`Cadmium hydroxide
`Charging Control
`Constant Voltage
`Digital-to-Analogue Converter
`Discharge Count Register
`Digital Cellular System
`Dimethyl carbonate
`Differential Quadrature Phase Shift Keying
`Digital Signal Processor
`DeskTop Charger
`Electron
`Ethylene carbonate
`Energy Conversion Control
`Enhanced Data rates for GSM Evolution
`Electro-Magnetic
`Ethyl methyl carbonate
`Electro-Motive Force
`Electro-Magnetic Interference
`Equivalent Series Resistance
`Frequency Division Duplex
`Frequency-Division Multiple Access
`Frequency Modulation
`Frequency Shift Keying
`Gaussian Minimum Shift Keying
`Global System for Mobile communication
`Proton
`Water
`Sulphuric acid
`High-Voltage IC
`Identification
`International Electrotechnical Commission
`Interface IC
`Potassium hydroxide
`Light-Emitting Diode
`Liquid-Crystal Display
`Linear Regulator
`Lithium-ion
`Lithium cobalt oxide
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`viii
`
`LiMn2O4
`Lithium manganese oxide
`Lithium nickel oxide
`LiNiO2
`Lithium hexafluorophosphate
`LiPF6
`Lithium graphite
`LiC6
`Last Measured Discharge
`LMD
`Least-Square Error
`LSE
`Minimum Shift Keying
`MSK
`Nominal Available Charge
`NAC
`North American Digital Cellular
`NADC
`Nickel-cadmium
`NiCd
`Nickel-metalhydride
`NiMH
`Ni(OH)2/NiOOH Nickel hydroxide/nickel oxyhydroxide
`NTC
`Negative-Temperature Coefficient resistor
`Oxygen
`O2
`OQPSK
`Offset Quadrature Phase Shift Keying
`Ox
`Oxidized species
`PA
`Power Amplifier
`Pb
`Lead
`Lead dioxide
`PbO2
`PCB
`Printed-Circuit Board
`PEO
`Polyethylene oxide
`PFC
`Programmed Full Count
`PM
`Power Module
`PTC
`Positive-Temperature Coefficient resistor
`PWM
`Pulse-Width Modulation
`QAM
`Quadrature Amplitude Modulation
`QPSK
`Quadrature Phase Shift Keying
`Red
`Reduced species
`RF
`Radio-Frequency
`Rx
`Receive
`SBC
`Smart Battery Charger
`SBD
`Smart Battery Data
`SBS
`Smart Battery System
`SEI
`Solid Electrolyte Interface
`SHE
`Standard Hydrogen reference Electrode
`SLA
`Sealed lead-acid
`SMBus
`System Management Bus
`SMPS
`Switched-Mode Power Supply
`SoC
`State-of-Charge
`SoH
`State-of-Health
`TCH
`Traffic Channel
`TCM
`Timer-Control Module
`TDD
`Time Division Duplex
`TDMA
`Time-Division Multiple Access
`Tx
`Transmit
`UMTS
`Universal Mobile Telecommunication System
`UPS
`Uninterruptible Power Supply
`VRLA
`Valve-regulated lead-acid
`Zinc-manganese dioxide
`Zn-MnO2
`3G
`Third Generation
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`Value
`
`List of symbols
`
`Symbol
`A
`A
`Abat
`max
`ACd
`ai
`ref
`ai
`b
`ai
`s
`ai
`ci
`b
`ci
`s
`ci
`Cch
`Cel
`Cth
`Cdl
`dl
`Co
`CH
`CG-C
`Cpara
`Caprem
`Capmax
`
`CFi
`Di
`di
`Dj
`
`dV/dtlim
`
`E
`
`Ei
`eq
`Ei
`Eeq
`bat
`Eeq*
`o
`Ei
`Eo
`bat
`Ea
`par
`Ech
`Eel
`Eth
`Emax
`
`Meaning
`Electrode surface area
`Area of spatial element
`Battery surface area
`Surface area of cadmium electrode
`Activity of species i
`Activity of species i in the reference state
`Bulk activity of species i
`Surface activity of species i
`Concentration of species i
`Bulk concentration of species i
`Surface concentration of species i
`Chemical capacitance
`Electrical capacitance
`Thermal capacitance
`Double-layer capacitance
`Double-layer capacitance per unit area
`Helmholtz capacitance
`Gouy-Chapman capacitance
`Parasitic capacitance in DC/DC converter
`Remaining battery capacity
`Maximum possible capacity that can be
`obtained from a battery
`Cost function for output variable i
`Diffusion coefficient of species i
`Diffusion layer thickness of species i
`Anti-parallel diodes that model Butler-
`Volmer relation for reaction j
`Change of battery voltage in time, used
`as parameter in proposed SoC indication
`system
`Error in ‘battery empty’ prediction of an
`SoC indication system
`Potential of electrode i
`Equilibrium potential of electrode i
`Equilibrium potential of battery, or EMF
`Apparent equilibrium potential
`Standard redox potential of electrode i
`Standard redox potential of battery
`Activation energy of parameter par
`Chemical energy
`Electrical energy
`“Thermal energy”
`Maximum energy stored in capacitor or
`coil
`
`ix
`
`Unit
`m2
`m2
`m2
`m2
`mol/m3
`mol/m3
`mol/m3
`mol/m3
`mol/m3
`mol/m3
`mol/m3
`mol2/J
`F
`J/K
`F
`F/m2
`F
`F
`F
`Ah
`Ah
`
`-
`m2/s
`m
`-
`
`V/s
`
`%
`
`V
`V
`V
`V
`V
`V
`J/mol
`J
`J
`JK
`J
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`Value
`
`96485
`
`Meaning
`Energy term, normalized to current, used
`in simple overpotential description of
`(Eq. 6.4)
`Faraday’s constant
`Channel frequency
`RF frequency
`Switching frequency in DC/DC converter
`Relation between measured battery
`parameter and SoC in direct-measurement
`SoC system
`Function that translates coulomb counter
`contents into SoC based on the basis of V,
`T and I measurements in a book-keeping
`system
`Exchange current for reaction j
`Anodic current
`Cathodic current
`Double-layer current
`Current level that determines state in
`proposed SoC indiction system
`Supply current
`Diffusion flux of species i
`Chemical flow
`Heat flow
`Reaction rate constant for oxidation
`(anodic) reaction j
`
`Reaction rate constant for reduction
`(cathodic) reaction j
`
`Backward reaction rate constant
`
`Forward reaction rate constant
`
`Oxygen solubility constant
`
`Thickness of nickel electrode, grain size
`Thickness of positive electrode, grain size
`Thickness of negative electrode, grain
`size
`Thickness of electrolyte in Li-ion model
`Number of electrons in reaction
`
`Unit
`J/A
`
`C/mol
`Hz
`Hz
`Hz
`%
`
`%
`
`A
`A
`A
`A
`A
`
`A
`mol/(m2.s)
`mol/s
`W
`Unit
`depends
`on
`reaction
`Unit
`depends
`on
`reaction
`Unit
`depends
`on
`reaction
`Unit
`depends
`on
`reaction
`mol/
`(m3.Pa)
`m
`m
`m
`
`m
`-
`
`x S
`
`ymbol
`Eq
`
`F
`fc
`fRF
`Fswitch
`d
`fT
`
`f bk
`
`V,T,I
`
`Io
`j
`Ia
`Ic
`Idl
`Ilim
`
`Isup
`Ji
`Jch
`Jth
`ka,j
`
`kc,j
`
`kb
`
`kf
`
`KO2
`
`lNi
`lpos
`lneg
`
`lelyt
`m
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` xi
`
`Value
`
`Symbol
`m
`
`M
`
`mi
`mref
`mo
`Cd
`MCd
`n
`n
`
`N
`N
`
`p
`P
`Pout
`Psup
`Pch
`Pel
`Pth
`Par(T)
`
`in
`
`the
`
`Meaning
`Number of spatial elements
`electrolyte in Li-ion model
`Number of parameter sets in optimization
`process
`Molar amount of species i
`Molar amount in the reference state
`Molar amount of cadmium nuclei at t=to
`Molecular weight of cadmium
`Number of electrons in reaction
`Number of capacitors
`in capacitive
`voltage converter
`Number of nuclei
`Number of points taken into account in
`optimization process
`Number of spatial elements in a system
`Pressure
`Output power of PA in cellular phone
`Supply power for PA
`Chemical power
`Electrical power
`“Thermal power”
`Temperature-dependent parameter
`
`paro
`
`Pre-exponential factor for parameter par
`
`Q
`Qth
`QCd,Max
`QNi,Max
`QCd(OH)2,Ni
`
`QCd,Cd
`
`LiCoO2
`LiC6
`
`Qmax
`Qmax
`r(t)
`R
`Rch
`Re
`Rleak
`
`Rbypass
`
`Rcoil
`
`Charge
`Heat
`Maximum capacity of cadmium electrode
`Maximum capacity of nickel electrode
`Overdischarge reserve of Cd(OH)2 at the
`nickel electrode
`Overdischarge reserve of cadmium at the
`cadmium electrode
`Maximum capacity of LiCoO2 electrode
`Maximum capacity of LiC6 electrode
`Radius of hemispherical particles
`Gas constant
`Chemical resistance
`Electrolyte resistance
`Resistance that models self-discharge in
`Li-ion model
`On-resistance of bypass switch in DC/DC
`converter
`ESR of coil in DC/DC converter
`
`8.314
`
`Unit
`-
`
`-
`
`mol
`mol
`mol
`kg/mol
`-
`-
`
`-
`-
`
`-
`Pa
`dBm
`W
`W
`W
`WK
`Unit
`depends
`on
`parameter
`Unit
`depends
`on
`parameter
`C
`J
`C
`C
`C
`
`C
`
`C
`C
`m
`J/(mol.K)
`Js/mol2
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`W
`W
`W
`W
`

`

`xii
`
`Symbol
`Rloss
`
`Rswitch
`
`Rel
`Rload
`
`Rth
`RS
`RW k
`Rd
`RdCd
`RkCk
`Si
`SoCE
`
`SoCS
`SoCt
`
`t
`trem
`t1,actual
`
`T
`T
`Tamb
`Toper
`Tperiod
`Upos,i
`
`Uneg,i
`
`Uq(I)
`
`V
`Vbat
`Vcon
`VEoD
`Verror
`
`Vnom
`Vsup
`Vsup,opt
`
`Vsup,min
`
`Meaning
`Ohmic-loss
`converter
`
`resistance
`
`in DC/DC
`
`Value
`
`Unit
`
`switch
`
`in DC/DC
`
`On-resistance of
`converter
`Electrical resistance
`Transformed antenna impedance seen at
`collector/drain of final PA stage
`Thermal resistance
`Series resistance of switch S
`Ohmic and kinetic resistance
`Diffusion resistance
`Time constant diffusion overpotential
`Time constant kinetic overpotential
`Switch i in DC/DC converter
`First SoC in equilibrium state, just after
`re-entry from transition state
`First SoC when discharge state is entered
`Last SoC in transition state just before
`equilibrium state is entered
`Time
`Remaining time of use
`Experimental remaining time of use from
`the moment a discharge current is applied
`until the battery is empty
`Switching period in DC/DC converter
`Temperature
`Ambient temperature
`Operating time
`Period time of burst drawn by PA model
`Interaction energy coefficient for LiCoO2
`electrode in phase i
`Interaction energy coefficient for LiC6
`electrode in phase i
`Inverse step function
`
`Voltage
`Battery voltage
`Control voltage
`End-of-Discharge voltage
`Error voltage in behavourial PA model
`
`Nominal supply voltage for PA
`Supply voltage
`Optimum supply voltage, as applied in
`efficiency control
`Minimum PA supply voltage at which
`linearity specification can still be met
`
`K/W
`
`s
`s
`-
`%
`
`%
`%
`
`s
`s
`s
`
`s
`K
`K
`s
`s
`-
`
`-
`
`-
`
`V
`V
`V
`V
`V
`
`V
`V
`V
`
`V
`
`1 for I£0
`and 0 for
`I>0
`
`Verror=0 or
`Verror=1
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`

` xiii
`
`Symbol
`Vswitch
`V(t)
`Vo
`
`Vg
`
`Vari
`
`Meaning
`Switch drive voltage in DC/DC converter
`Volume of deposited material at time t
`Initial volume of hemispherical particles
`at time to
`Free gas volume inside battery
`
`Value
`
`Output variable in optimization process
`
`Unit
`V
`m3
`m3
`
`m3
`
`Depends
`on Vari
`Depends
`on Vari
`m
`-
`-
`-
`
`-
`
`-
`-
`W/(K.m2)
`-
`mol/
`(m3.Pa)
`m
`-
`m
`-
`J/mol
`
`J/mol
`
`J/mol
`
`J/mol
`
`J/mol
`
`J/mol
`
`J/mol
`J/(mol.K)
`m
`C2/(N.m2)
`-
`V
`V
`V
`
`1, see note 1
`
`0<a <1
`
`1, see note 1
`
`0<d<1
`
`0<d PA<1
`
`8.85.10-12
`
`Wi,j
`
`x
`xj, yj, zj
`xi
`xpos
`
`Normalizing and weighing factor for
`output variable Vari
`Distance
`Reaction order of species in reaction j
`Mol fraction of species i
`phasetransition Mol fraction of Li+ ions at which phase
`transition occurs in positive electrode
`phasetransition Mol fraction of Li+ ions at which phase
`transition occurs in negative electrode
`Valence of ionic species i
`Transfer coefficient
`Heat transfer coefficient
`Activity coefficient
`Fugacity coefficient
`
`Diffusion layer thickness
`Duty cycle in DC/DC converter
`Helmholtz layer thickness
`Duty cycle of PA = ON/OFF ratio
`Gibbs free energy change under standard
`conditions
`Gibbs free energy change under standard
`conditions, taking constant activity terms
`for e.g. OH- or H2O into account
`Change in (Gibbs) free energy in an
`oxidation reaction
`Change in (Gibbs) free energy in a
`reduction reaction
`Change in free electrochemical energy in
`an oxidation reaction
`Change in free electrochemical energy in
`a reduction reaction
`Change in a reaction’s enthalpy
`Change in a reaction’s entropy
`Thickness of a spatial element
`Permittivity in free space
`Dielectric constant
`Electrostatic or Galvani potential
`Electrostatic electrode potential
`Electrostatic electrode potential
`
`xneg
`
`zi
`a
`a th
`g
`gg
`d
`d
`d H
`d PA
`D Go
`
`D Go’
`
`D GO
`D GR
`
`OGD
`RGD
`D H
`D S
`D x
`eo
`er
`f
`f e
`f s
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`xiv
`
`Symbol
`f l
`f Ox
`
`i
`o
`
`F i
`2F
`m i
`m
`m i
`r Cd
`n i
`t
`td
`tq
`w RF
`h ct
`h d
`h k
`h W
`h W k
`h q
`h DC/DC
`h max
`h max,theory
`h PA
`q ex
`z pos,i
`z neg,i
`
`Meaning
`Electrostatic electrolyte potential
`Electrostatic potential of Ox
`electrolyte
`
`ions
`
`in
`
`Value
`
`switch
`
`in
`
`for
`period
`Conduction
`capacitive voltage converter
`Conduction angle for PA
`Chemical potential of species i
`Electrochemical potential of species i
`Standard chemical potential of species i
`Gravimetric density of cadmium
`Stoichiometric factors for species i in a
`reaction equation
`Time constant
`Diffusion time constant
`Time constant associated with increase in
`overpotential in an almost empty battery
`RF angular frequency
`Overpotential of charge transfer reaction
`Diffusion overpotential
`Kinetic overpotential
`Ohmic overpotential
`Combined
`ohmic
`overpotential
`Increase in overpotential when the battery
`becomes empty
`DC/DC converter efficiency
`Maximum attainable PA efficiency
`Maximum theoretical PA efficiency
`PA efficiency
`Extended surface area
`Constant for LiCoO2 electrode in phase i
`Constant for LiC6 electrode in phase i
`
`and
`
`kinetic
`
`Unit
`V
`V
`
`s
`
`rad
`J/mol
`J/mol
`J/mol
`kg/m3
`-
`
`s
`s
`s
`
`rad/s
`V
`V
`V
`V
`V
`
`V
`
`%
`%
`%
`%
`m2
`-
`-
`
`Note 1: Value of 1 has been assumed in this thesis
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`1
`
`Chapter 1
`Introduction
`
`1.1 The energy chain
`The demand for portable electronic consumer products is rapidly increasing.
`Examples of fast-growing markets of portable products are notebook computers,
`cellular and cordless phones and camcorders. Figure 1.1 shows the expected world-
`wide shipment of cellular handsets until the year 2004 [1], with the total number of
`handsets sold increasing dramatically. At present, almost half of the shipments of
`cellular handsets are replacement sales, which means that people who already have a
`cellular phone buy them. By 2004, almost all cellular handsets sold will be
`replacement sales.
`
`1998
`58
`105
`
`1999
`112
`168
`
`2000
`215
`243
`
`2001
`360
`290
`
`2002
`556
`220
`
`2003
`701
`110
`
`2004
`771
`60
`
`900
`
`800
`
`700
`
`600
`
`500
`
`400
`
`300
`
`200
`
`100
`
`0
`
`M pcs
`
`Replacement sales
`New subscribers
`
`Figure 1.1: Expected world-wide shipments of cellular handsets in millions per type of sales
`[1]
`
`In view of battery costs and environmental considerations, the batteries used to
`power these portable devices should preferably be rechargeable. The demand for
`rechargeable batteries is increasing in line with that for portable products. Table 1.1
`shows the sales of the most important rechargeable battery types in Japan in 1998
`[2]. The majority of the rechargeable batteries are manufactured in Japan. Table 1.1
`shows that the number of batteries sold increased dramatically in 1998 relative to
`1997. More information on rechargeable battery types will be given in chapter 3.
`The energy yielded by a portable device in the form of, for example, sound or
`motion, ultimately derives from the electrical energy supplied by the mains. The
`conversion of energy from the mains to the eventual load inside a portable product
`can be described as an energy chain [3], which is shown in Figure 1.2. The links of
`the energy chain are a charger, a battery, a DC/DC converter and a load.
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`2 Chapter 1
`
`Table 1.1: Sales of the most important rechargeable battery types in Japan in millions in 1998
`[2]
`
`Battery type
`NiCd
`NiMH
`Li-ion
`
`Sales in 1998 (1M pieces)
`588
`640
`275
`
`Growth with respect to 1997
`85%
`112%
`141%
`
`e l e ctrical
`
`m a gnetic
`
`e l e ctrical
`
`c h emical
`
`e l e ctrical
`
`m a gnetic
`
`e l e ctrical
`
`mains
`
`charger
`
`battery
`
`DC/DC
`
`visi o
`
`n m o tion soun
`load
`
`d
`
`EM rad i a t i
`
`n
`
`o
`
`monitor and control
`
`Figure 1.2: The energy chain symbolizing the energy transfers from mains to load in a
`portable product
`
`Electrical energy from the mains is fed to the battery through the charger during
`charging. The charger uses electromagnetic components like a transformer or an
`inductor. Here, electrical energy from the mains is first transformed into magnetic
`energy and then back into electrical energy. The battery stores the electrical energy
`in the form of chemical energy. During discharge of the battery, chemical energy is
`converted back into electrical energy.
`The DC/DC converter is an optional link. It is not to be found in every portable
`product. There are two reasons for its presence. First of all, the battery might deliver
`a voltage which is not suitable for operation of the load. Secondly, each circuit part
`of the load should be operated from the lowest possible supply voltage for efficiency
`reasons, because a surplus in supply voltage is often dissipated in the form of heat.
`In both cases, the DC/DC converter powers the load with the lowest possible supply
`voltage, irrespective of the battery voltage. The DC/DC converter uses an inductor,
`which translates the electrical energy from the battery into magnetic energy and
`back into electrical energy again. In the load, the electrical energy from the DC/DC
`converter is converted into sound, light, Electro-Magnetic (EM) radiation or
`mechanical energy.
`In order to make optimum use of the energy inside the battery, all conversions
`of energy in the energy chain should be well understood and made as efficient as
`possible. This is especially true when miniaturization of the portable product is
`desired. Miniaturization is an important trend for many portable devices. Portable
`phones, for example, are becoming smaller and smaller. When the volume of a
`portable device decreases, the amount of dissipated power must also decrease. The
`reason is that a smaller volume will yield a higher temperature when the amount of
`dissipated power remains the same. There is also a trend towards increasing
`complexity and functionality of portable products. An example is e-mail and internet
`facilities added to the functionality of cellular phones. Adding complexity to the
`total system adds to the total power consumption of the load. So assuring efficient
`energy conversions becomes even more important. This can be achieved by
`monitoring and controlling all the links in the energy chain. This is schematically
`shown in Figure 1.2.
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`Introduction 3
`
`There are algorithms that check and control the links in the energy chain. A first
`example is a charging algorithm, which keeps track of the battery status and controls
`the charger by interrupting the charging current when the battery is full. Charging
`should not continue once the battery is full, because otherwise the battery
`temperature will rise substantially and/or the battery might be damaged. This
`decreases its capacity and usable number of cycles. Therefore, a proper charging
`algorithm leads to a more efficient use of the battery and its energy.
`A second example is an algorithm that determines the battery’s State-of-
`Charge (SoC). This information can be used to make more efficient use of the
`battery energy. For example, it can be used as input for charge control, indicating
`that the battery is full. Also, it is more likely that the user will wait longer before
`recharging the battery when an accurate and reliable SoC indication is available on a
`portable device. Less frequent recharging is beneficial for the cycle life of the
`battery.
`A third example is an algorithm that controls a DC/DC converter to power the
`load with the minimum required supply voltage, dependent on the activity of the
`load. An example of such a load is a Power Amplifier (PA) in a cellular phone. In
`the case of a PA, the supply voltage may be lower for lower output power. This
`leads to better efficiency. This example will be elaborated in chapter 7.
`
`1.2 Definition of a Battery Management System
`Three terms apply to the implementation of monitor and control functions in the
`energy chain. These terms are battery management, power management and energy
`management. As a rough indication, battery management involves implementing
`functions that ensure optimum use of the battery in a portable device. Examples of
`such functions are proper charging handling and protecting the battery from misuse.
`Power management involves the implementation of functions that ensure a proper
`distribution of power through the system and minimum power consumption by each
`system part. Examples are active hardware and software design changes for
`minimizing power consumption, such as reducing clock rates in digital system parts
`and powering down system parts that are not in use. Energy management involves
`implementing functions that ensure that energy conversions in a system are made as
`efficient as possible. It also involves handling the storage of energy in a system. An
`example is applying zero-voltage and zero-current switching to reduce switching
`losses in a Switched-Mode Power Supply (SMPS). This increases the efficiency of
`energy transfer from the mains to the battery.
`It should be noted that the implementation of a certain function may involve
`more than one of the three management terms simultaneously. This thesis will focus
`on battery management and its inclusion in a system. A definition of the basic task
`of a Battery Management System can be given as follows:
`
`The basic task of a Battery Management System (BMS) is to ensure that
`optimum use is made of the energy inside the battery powering the portable
`product and that the risk of damage inflicted upon the battery is minimized.
`This is achieved by monitoring and controlling the battery’s charging and
`discharging process.
`
`Keeping in mind the examples of algorithms given in section 1.1, this basic task of a
`BMS can be achieved by performing the following functions:
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`4 Chapter 1
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`• Control charging of the battery, with practically no overcharging, to ensure a
`long cycle life of the battery.
`• Monitor the discharge of the battery to prevent damage inflicted on the battery
`by interrupting the discharge current when the battery is empty.
`• Keep track of the battery’s SoC and use the determined value to control
`charging and discharging of the battery and signal the value to the user of the
`portable device.
`• Power the load with a minimum supply voltage, irrespective of the battery
`voltage, using DC/DC conversion to achieve a longer run time of the portable
`device.
`
`1.3 Motivation of the research described in this thesis
`As described in section 1.1, more efficient use of the energy inside a battery is
`becoming increasingly important in the rapidly growing market for portable
`products. Manufacturers of portable devices are consequently paying even more
`attention to battery management. This is reflected in many commercial electronics
`magazines, such as Electronic Design and EDN, containing examples of
`implementations of battery management functions in a system. Many examples are
`to be found of ICs that implement certain charge algorithms [4]-[7]. Adding
`intelligence to batteries in portable products to enable e.g. SoC monitoring is also
`receiving a great deal of attention. The term ‘smart battery’ is a general buzzword
`that pops up in many articles [5],[8]-[10]. However, no explanation of battery
`behaviour is given in this kind of magazines. Therefore, the reason why one battery
`management IC performs better than another is often not understood. Moreover, it is
`hard to determine how the functionality of a BMS can be improved.
`Besides in the magazines mentioned above, a lot of information on battery
`management can also be found in the literature. For example, much attention is paid
`to finding ways of accurately determining a battery’s SoC [11]-[13]. The battery
`management functions described in these articles are derived from extensive battery
`measurements,