Project 2 Thermal modeling of battery pack
AIM:
For a 10 cell series lithium ion battery model, simulate the thermal effects and compare life cycle performance at various temperatures, charge & discharge rates using MATLAB and Simulink.
OBJECTIVE:
- Simulate the thermal effects of lithium ion battery.
- Compare life cycle performance at various temperatures, charge and discharge rates.
Theory:
Now a days lithium ion battery are mostly used in electric vehicles we must know its charge and discharge rates to operate this batterys in efficient manner and with out damage when this batterys in operation this temperature of it must be kept in limit we simulate the thermal effect of this cell , by knowing the how much temp rise take place we can provide efficient cooling to the batterys so that the life cycle of the battery increases.We know that the temperature measured at the poles of a dynamically loaded battery varies to the relevant cell temperature. Hence, the accuracy of the measurement at the poles is limited. Therefore a thermal model of the battery is used in order to calculate the cell temperature.
Simulink model:
A detail design of MATLAB Simulink model for thermal modelling is given as:-
Cell 01 to 04 Subsystem:
Cell subsystem basically consist of a Thermal Model and Lithium Cell 1RC block which calculate the temperature and thermal effect for cells and overall calculate for the battery pack.
The block which are inside the cell subsystem are PS Gain block which multiplies the input physical signal by a constant i.e. y = u.* gain. Another block are voltage sensor and current voltage source.
The voltage sensor block represents an ideal voltage sensor, that is, a device that converts voltage measured between any electrical connections into a physical signal proportional to the voltage.
Current voltage source represents an ideal voltage source that is powerful enough to maintain the specified voltage at its output regardless of the current passing through it. The output voltage is V = Vs, where Vs is the numerical value presented at the physical signal port.
Thermal Model Subsystem:
The important block which is inside the thermal model subsystem are:
- Thermal Reference: This block represents a reference point in a thermal network where the temperature is equal to absolute zero.
- Controlled heat flow rate source: This block represents an ideal energy source in a thermal network that can maintain a controlled heat flow rate regardless of the temperature difference. The heat flow rate is set by the physical signal port S. A positive heat flow rate flows from port A to port B.
- Thermal Mass: This block models internal energy storage in a thermal network. The rate of temperature increase is proportional to the heat flow rate into the material and inversely proportional to the mass and specific heat of the material.
- Temperature Sensor: This block measures temperature in a thermal network. There is no heat flow through the sensor. The physical signal port T reports the temperature difference across the sensor. The measurement is positive when the temperature at port A is greater than the temperature at port B.
Lithium Cell 1RC Subsystem:
This block basically consists of capacitance value © table which depends on an external physical signal inputs SOC and T. It is assumed that the capacitance value is slowly varying with time, and hence the equation i = C*dv/dt holds.
Resistance value (R) table which depends on an external physical signal inputs SOC and T.
Voltage value (EM) which implements the cell's main branch voltage source, and determines values for capacity (C) and state of charge (SOC). The defining equations depend on cell temperature, T.
Thermal behaviour and fault setup:
Lithium-ion cell one RC-Branch equivalent circuit detail for 10 cells.
For cell 01 to 04
- Number of series-connected cells are 4
- Initial Temperature is 299.1 K
For cell 05 (fault setup) In this cell I have done some changes in Electrical system of cell so that we can see the fault.
- Number of series-connected cells are 1
- Initial Temperature is 299.1 K
- Capacity (A*hr) = Capacity_LUT*0.95
- Em open-circuit voltage (volts) = Em_LUT*0.9
- R0 terminal resistance (ohms) = R0_LUT*5
- R1 cell resistance (ohms) = R1_LUT*5
- C1 capacitance (farads) = C1_LUT*0.95
For cell 06 to 10
- Number of series-connected cells are 5
- Initial Temperature is 299.1 K
Here the output of one cell is connected with the SOC calculation whereas other output is connected with AC current source for cyclic charge/discharge profile.
The peak amplitudes set to 50 A for cyclic charge and discharge. A basic parameter of AC current source is as
The ideal AC current source maintains the sinusoidal current through it, independent of the voltage across its terminals. The output current is defined by I = I0 * sin(2*pi*f*t + PHI), where I0 is the peak amplitude, f is the frequency in Hz, and PHI is the phase shift in radians.
The other block which are used in lithium ion battery pack are as:
- Temperature Source: This block represents an ideal energy source in a thermal network that can maintain a constant absolute temperature at the port regardless of the heat flow rate.
This block is used for ambient temperature and which I set as 299.1 K or 25.95 C.
Convective Heat Transfer: This block models heat transfer in a thermal network by convection due to fluid motion. The rate of heat transfer is proportional to the temperature difference, heat transfer coefficient, and surface area in contact with the fluid.
Used 3 blocks for convection.
Conductive Heat Transfer: This block models heat transfer in a thermal network by conduction through a layer of material. The rate of heat transfer is governed by Fourier's law and is proportional to the temperature difference, material thermal conductivity, area normal to the heat flow direction, and inversely proportional to the layer thickness.
The conduction is done from the 2 set of blocks, 1 block is used for 01-04 and other is used for cell 06-10.
For SOC calculation Gain block, Integrator and Sum block with PS simulink convertor was used.
Results:
Simulation based on different cell temperature:
In this simulation, ambient temperatures were set at 299.1 K or 25.95 C and another cell temperature are as follows:
Colour Indication for cells
- Yellow colour – Cell 4
- Purple colour – Cell 5 (Fault)
- Green colour – Cell 10
Test-1 (Equal Temperature):
As we can see that there is much fluctuation in cell 05 due to fault.
Calculated SOC:
As we see that the battery is fluctuating every 301.200 seconds which depend upon the thermal behaviour of battery pack.
Conduction:
Conduction is basically here Heat Flow rate (Q) and Temperature Difference (T) Vs Time.
Convection:
Below graph highlight the heat flow rate and temperature difference by convection medium.
Cyclic charge / discharge profile:
Charge and discharge profile are depending upon Current (I) and Voltage (V) vs Time. The cyclic charge and discharge were calculated at 50A peek amplitude.
Test-2 (Cell 5 minimum temperature):
As we can see that in cell 5 the temperature rice till 312 and it goes fluctuating from 313 K to 307 K and end at 311 k.
Calculated SOC:
As we see that the battery is fluctuating every 301.200 seconds which depend upon the thermal behaviour of battery pack.
Conduction:
Conduction is basically here Heat Flow rate (Q) and Temperature Difference (T) Vs Time.
Convection:
Below graph highlight the heat flow rate and temperature difference by convection medium.
Cyclic charge / discharge profile:
Charge and discharge profile are depending upon Current (I) and Voltage (V) vs Time. The cyclic charge and discharge were calculated at 50A peek amplitude.
Test-3 (Low to High Temperature):
As we can see that in cell 5 the temperature quickly falls and it fluctuate for 5 k and end at 307 K.
Calculated SOC:
As we see that the battery is fluctuating every 301.200 seconds which depend upon the thermal behaviour of battery pack.
Conduction:
Conduction is basically here Heat Flow rate (Q) and Temperature Difference (T) Vs Time.
Convection:
Below graph highlight the heat flow rate and temperature difference by convection Medium.
Cyclic charge / discharge profile:
Charge and discharge profile are depending upon Current (I) and Voltage (V) vs Time. The cyclic charge and discharge were calculated at 50A peek amplitude.
Test-4 (High to Low Temperature):
As we can see that in cell 5 the temperature quickly falls and it fluctuate for 5 k and end at 309 K.
Calculated SOC:
As we see that the battery is fluctuating every 301.200 seconds which depend upon the thermal behaviour of battery pack.
Conduction:
Conduction is basically here Heat Flow rate (Q) and Temperature Difference (T) Vs Time.
Convection:
Below graph highlight the heat flow rate and temperature difference by convection Medium.
Cyclic charge / discharge profile:
Charge and discharge profile are depending upon Current (I) and Voltage (V) vs Time. The cyclic charge and discharge were calculated at 50A peek amplitude.
Test-5 (Cell – 5 Maximum Temperature):
As we can see that in cell 5 the temperature quickly falls and it fluctuate for 5 k and end at 309 K.
Calculated SOC:
As we see that the battery is fluctuating every 301.200 seconds which depend upon the thermal behaviour of battery pack.
Conduction:
Conduction is basically here Heat Flow rate (Q) and Temperature Difference (T) Vs Time.
Convection:
Below graph highlight the heat flow rate and temperature difference by convection Medium.
Cyclic charge / discharge profile:
Charge and discharge profile are depending upon Current (I) and Voltage (V) vs Time. The cyclic charge and discharge were calculated at 50A peek amplitude.
Conclusion:
- The flow of heat is decreased at constant and minimum temperature that is 309 k for different temperature based.
- Based on different temperature we will see changes in conduction and convection.
- There is slightly changes in cyclic charge and discharge of cell which I fixed at 50A as peek amplitude.
- As I set fault in cell-5 and we can see that there is lots of fluctuation and temperature rise in cell-5 as compared with other cells connected in series.
SOC for all different temperature are same, there is no changes in SOC.
Source of the model taken from the below MATLAB link:
https://in.mathworks.com/help/physmod/simscape/ug/lithium-ion-battery-pack-with-fault.html