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.

Introduction: The Lithium-ion batteries are widely used as energy sources in different hybrid and electric vehicle, however the operation characteristics of the battery in such vehicle are strongly dependent on the operation temperature and therefore, with purpose to improve these characteristics a good thermal control system should be utilized.

The temperature effact of a Lithium-ion battery cell is important for its performance, efficiency, safety, and capacity. It is influenced by the environmental temperature and by the charging and discharging process also. Therefore, a thermal model of the battery is used in order to calculate and estimate the cell temperature.

Procedure:

• 10 lithium-ion battery cells are connected in with the combination of three packs the 1st consistent 4 cells in series, 2nd pack consist of 1 cell which set to design as fault for study purpose to observe temperature changes within battery pack and the 3rd pack contain 5 cells in series.
• The heat transfer is observed between the packs by conduction and convection block which are modes of heat transfer.
• T subsystem is attached in between every pack to plot the temperature graph of the cell of that particular battery pack.
• Also external ambient temperature source is attached and also thermal sensor is attached to the same. to indicate the value in the display.
• This battery pack is connected to AC current source to observe the cyclic charge and discharge rate graph.
• Also we added a current sensor in between the battery pack and AC current source to calculate the SOC of the battery
• The cell temperature and soc graphs are plotted in scope which indicating the temperature of cell no 5, and cell no 10.
• All the other results are located in the simscape result menu.

MATLAB Model: simulink model of 10 cells series Lithium-Ion battery model using an AC source with cyclic charge/discharge profile.

• Lithium-Ion Battery Pack with Fault is to simulate a battery pack consisting of multiple series-connected cells in an efficient manner.
• It also shows how a fault can be introduced into one of the cells to see the impact on battery performance and cell temperatures.
• For efficiency, identical series-connected cells are not just simply modelled by connecting cell models in series. Instead a single cell is used, and the terminal voltage scaled up by the number of cells.
• The fault is represented by changing the parameters for the Cell 5 Fault subsystem, reducing both capacity and open-circuit voltage, and increasing the resistance values.

Blocks Used:

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 subsystems are PS gain block which multiplies the input physical signals 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, this is a device that converts voltage measured between any electric connection into a physical signal proportional to the voltage.
• The 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 numeric value represents 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.

• 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. Following blocks shows the Convection block values for different cells.

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.

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.

Cell 01 to 04:

• Number of series-connected cells are 4.
• Initial Temperature is 299.1 K.

Cell no. 5: 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

Cell 06 to 10:

• Number of series-connected cells are 5
• Initial Temperature is 299.1 K

AC Current Source: The AC Current Source block represents an ideal current source that maintains the sinusoidal current through it, independent of the voltage across its terminals. The output current is defined by the following equation: `I=I_0⋅sin(2π⋅f⋅t+φ)`

The peak amplitude is set to 50 A for a cyclic charge and discharge. A basic parameter of AC source is as,

Results.

Cell temperature and SOC: All the three the cell having the same temperature at the start which is at 299.1 k. But in the beginning few seconds of simulation cell no 5 oscillates with more the cell 4 and 10 because its design with fault and ranging to higher temp then cell 4 and 10. After a time period of around 1300 sec both the cells getting are unfollowing the temperature line which was following the same temperature rate, cell no 4 and 10 having approximately 315(cell 04 having quite less temp then cell 10 because of no of the cell are different) k at the end of the simulation and the cell no 5 achieving the higher temperature of around 328 k.

The SOC graph following the sinusoidal waveform structure and fluctuating after 297 seconds and this waveform achieving the value of more than 100.06 soc.

Conduction:

For cell 01-04: For the cell 01-04 the value at the end of the simulations are, The heat transfer coefficient is 21.32 W/(m²K), Thermal conductivity 10.66 W/m K.

For Cell 05: For cell 05 the values at the end of the simulation are, The heat transfer coefficient is 20.12 W/(m²K), Thermal conductivity 10.06 W/m K.

Convecction Ambient Cell: 06-09 for cell 06-10 the values at the end of the simulation are,The heat transfer coefficient is -72.32 W/(m²K),Thermal conductivity -16.22 W/m K.

Convecction Ambient Cell 10: the values at the end of the simulation are,The heat transfer coefficient is -12.32 W/(m²K),Thermal conductivity -26.22 W/m K

Current Sensor:

Cyclic Charge// Discharge Profile:

Rsults: With Ambient Temperature 299 K, Cell temperature (01-04) 310K, Cell temperature (05) 320K, Cell temperature (06-10) 330K.

Cell temperature and SOC: The initial temperature for cell no 04 is 310K, cell no 5 is 320 K and cell no 10 is 330K, but after some point, cell no 04 and cell no. 10 started following the same temperate rate, and cell no 5 starts oscillating with high value because of fault. the final value for cell no 04 and 10 is around 316K and fro cell no 5 is 328K because of its fault design.

The SOC graph following the sinusoidal waveform structure and fluctuating after 297 seconds and this waveform achieving the value of more than 100.06 soc.

Conduction Cell 1-4:

Conduction Cell 5:

Convection Ambient- Cell 01-09:

Convection Ambient- Cell 10:

Convection Ambient- Cell 6-10:

Cyclic Charge/Discharge Profile:

CONCLUSIONS:

• As the difference in temperature we can observe the changes in heat flow rate by conduction and convection.
• There are slight changes in cyclic charge and discharge as we fixed peak amplitude at 50 A.
• SOC for all the temperature remain the same so there is no difference in SOC graphs.
• Cell no 5 had higher oscillation and we can observe that in every graph because we design that cell for fault.