effective modeling of temperature effects on lithium polymer cells
TRANSCRIPT
Effective Modeling of Temperature Effects
on Lithium Polymer Cells
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
2
Outline
• Introduction
• Cell model
• Model characterization
Experimental set-up
Test description
Parameter extraction
Thermal model
• Model validation
• Conclusions
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
3
Introduction – Lithium Battery
Model TypeCapacity
[Ah]
Max continuous current [A] Energy
density[Wh/kg]
Power density[W/kg]
Cycle Life
Charge Discharge
Saft VH AA 1500 Ni-MH 1.5 4.2 4.2 69 194 NA
Saft VL34P Li-ion 33 500 120 128 7378 NA
Kokam SLPB78216216H
LiPo 31 155 62 133 1334 >800
ThunderSky-LYP40AHA
LiFePO4 40 120 120 85 1707 >3000
Altairnano 50AhNano
LithiumTitanate
50 300 300 72 719 >4000
• Lithium batteries very promising for next generation hybrid and electric vehicles
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
4
Introduction - Lithium Battery (cont’d)• Battery management systems (BMSs) needed for
safe and reliable operation of the vehicle battery Monitor cell voltage and temperature
Evaluate state-of-charge (SOC) and state-of-health (SOH)
• Accurate cell model to be embedded in the BMS for SOC and SOH estimate
to be used for BMS design and simulation
• In this work, a scaled model of LiPo cell is considered Kokam SLPB723870H4 1.5 Ah, 1.5 A max charge current,
30 A max continuous discharge current
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
5
Electrical Cell model
M. Chen et al. “Accurate Electrical Battery Model Capable of predicting Runtime and I-V Performance,” IEEE Trans. Energy Convers., vol. 21, no. 2, June 2006
Model Parameter Symbol DependenceCell capacity Ccapacity -
Self discharge Rself_discharge -
Ohmic resistence Rseries Icell, SOC, T
Long transient RC Rt_long / Ct_long Icell, SOC, T
Short transient RC Rt_short / Ct_short Icell, SOC, T
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
6
Experimental set-up
• Standard set-up combined with a custom-designed temperature-controlled chamber
TTi LD300 80V-80A
TTi QL355TP 35V-5A
NI USB - 6008
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
7
• Cell encased in two symmetrical halves. Each of them contains: Array of digital temperature sensors 82 W Peltier TEC
Temperature-controlled chamber
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
8
Temperature effect on cell behavior
• 1C rate discharge at different cell temperatures
• As known, temperature significantly affects cell behavior decreasing the usable cell capacity
end-of-discharge voltage
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
9
Cell model parameter extraction
• Test procedure:
• Test conditions: Charge current (Itest): 0.5C, 1C rates
Discharge current (Itest): 0.5C, 1C, 5C, 10C, 20C rates
Cell temperature: 10, 25, 35 °C
C - Used to signify a charge or discharge rate equal to the capacity of a battery divided by 1 hour.
Init phase:•1C charge•1 h pause•1C discharge
Pause phase:•1 h pause
Test phase:•charge/discharge cycle •current and temperature of interest•5 min pause after 1% SOC variation and every 9% SOC variation
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
10
Cell model parameter extraction (cont’d)
• Model parameters derived from the cell voltage transient during the 5 min pauses
charge cycle discharge cyclepause
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
11
Cell model parameter extraction (cont’d)
RseriesIcell
short Rt _ short Ct _ short
long Rt _ long Ct _ long
A Rt _ short Icell
B Rt _ long Icellpause (Icell = 0)Icell = Itest Icell = Itest
longshort
tt
occell BeAeVtV
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
12
Cell model parameters
• Open Circuit Voltage (OCV) Extracted from 1C charge/discharge Small dependence on cell temperature
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
13
Cell model parameters (cont’d)
• Let’s have a look at Rtot=Rseries+Rt_long+Rt_short
• As expected, Rtot increases at lower temperatures
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
14
Thermal Model
• The electrical model has been improved with a first order thermal model
• Cth and Rth estimated by observing the thermal evolution of the cell
dtR
TTQ
CTT
th
ambcell
thambcell
1
cellcelloc IVVQ
Param. Value
Cth 50 W/°C
Rth 14.7 °C/W
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
15
• Model implemented in Matlab/Simulink® using multidimensional LUT for model parameters
Model validation
Model 25 °C Model Model T
Max RMS Max RMS Max RMS
Abs error 398 mV 49 mV 181 mV 14 mV 181 mV 14 mV
% error 9.61 % 1.45 % 5.6 % 0.39 % 5.6 % 0.39 %
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
16
Model validation (cont’d)
Model 25 °C Model Model T
Max RMS Max RMS Max RMS
Abs error 521 mV 26 mV 478 mV 17 mV 486 mV 17 mV
% error 12.6 % 0.69 % 11.5 % 0.44 % 11.7 % 0.44 %
F. Baronti et al. - Effective modeling of temperature effects on lithium polymer cells
17
• Experimental characterization of a1.5 Ah Kokam LiPo cell
• Accurate modeling including thermal effects
• Model implemented in Matlab/Simulink®
Very good matching between experimental and simulated dynamic cell behaviors
Model accuracy significantly improves iftemperature-dependent parameters are used
• Starting point for the design and simulation of the battery pack and BMS using 31 Ah Kokam LiPo cells targeting a Fuel Cell HEV
Conclusions