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AIM

To simulate the thermal effects and compare life cycle performance at various temperatures, charge, and discharge rates for a 10-cell series lithium-ion battery model using MATLAB SIMULINK.

THEORY

In today's electric vehicles, lithium-ion batteries are predominantly used. Understanding their charge and discharge rates is crucial to operating these batteries efficiently and preventing damage. Managing the temperature during operation is essential, as excessive heat can affect the battery's life cycle. By simulating the thermal effects, we can determine the temperature rise and provide effective cooling, thereby increasing the battery's lifespan. The following model illustrates this concept, with explanations provided.

Cells are connected in series, and one cell is made faulty to study its thermal effects. This example demonstrates how to simulate a battery pack with multiple series-connected cells efficiently and how a fault in one cell impacts performance and temperatures. Instead of simply modeling identical series-connected cells by connecting individual cell models in series, a single cell model is used, and the terminal voltage is scaled by the number of cells. The fault is represented by altering the parameters for the Cell 10 Fault subsystem, reducing capacity and open-circuit voltage, and increasing resistance values.

SIMULINK MODEL

For the 10-cell series lithium-ion battery model, MATLAB and Simulink were used to analyze thermal effects and life cycle performance concerning temperature, charge, and discharge rates. Conduction and convection blocks were also used to demonstrate heat transfer in battery packs.

The model simulates a battery pack with multiple series-connected cells, including a fault in one cell to observe the impact on performance and temperatures. The fault is introduced by modifying the electrical parameters of the cell, reducing its capacity and open-circuit voltage, and increasing resistance values.

Connection Details

The 10 lithium-ion battery cells are connected in three packs: the first pack contains 4 cells in series, the second pack contains 1 cell designed with a fault for study purposes, and the third pack contains 5 cells in series.

Heat transfer between packs is observed using conduction and convection blocks. Temperature sensors are placed between each pack to plot the temperature graphs of individual cells. An external ambient temperature source and thermal sensors are used to indicate values on display.

The battery pack is connected to an AC current source to observe the cyclic charge and discharge rate graph. A current sensor is added between the battery pack and AC current source to calculate the State of Charge (SOC) of the battery. Cell temperature and SOC graphs are plotted, indicating temperatures for cell 4, cell 5, and cell 10. Other results are located in the Simscape results menu.

Cell Subsystems

The cell subsystem includes a thermal model and lithium cell IRC block to calculate the temperature and thermal effects for individual cells and the overall battery pack. Key blocks include:

· PS Gain Block: Multiplies the input physical signals by a constant.

· Voltage Sensor Block: Converts voltage measurements into physical signals proportional to the voltage.

· Current-Voltage Source: Represents an ideal voltage source maintaining specified voltage regardless of current.

Thermal Model

The thermal model includes various blocks such as:

· Controlled Heat Flow Rate Source: Represents an ideal source of thermal energy, maintaining specified heat flow at its outlet regardless of temperature difference.

· Thermal Reference: Represents a thermal reference point with absolute zero temperature.

· Thermal Mass: Represents a material's ability to store internal energy, characterized by mass and specific heat.

· Temperature Sensor: An ideal sensor determining temperature differential between two points without drawing heat.

Lithium Cell 1RC Subsystem

This block includes:

· Capacitor Value Table: Varies with SOC and temperature.

· Resistance Value Table: Depends on SOC and temperature.

· Voltage Value (EM): Implements the cell's main branch voltage source.

Fault Setup

For the faulty cell (Cell 5), changes in the electrical system parameters were made to observe the fault's impact:

· Number of Cells in Series: 4

· Initial Temperature: 299.1 K

· Capacity (A/hr): Reduced by 5%

· Open-Circuit Voltage (EM): Reduced by 10%

· Terminal Resistance (RO): Increased by 5 times

· Cell Resistance (R1): Increased by 5 times

· Capacitance (C1): Reduced by 5%

PARAMETERS

· Battery Configuration:

o Temperature Source: Maintains a constant temperature of 299.1 K or 25.95°C.

o Conductive Heat Transfer: Represents heat transfer by conduction.

o Convective Heat Transfer: Represents heat transfer by convection.

o Temperature Sensor: Measures temperature differential.

o Electrical Elements: Includes an AC current source for cyclic charge/discharge profiles and a current sensor for SOC calculation.

For the study ,we have some observation where we getting results for different cell temperature

here we have set ambient temperature is 299.1k or25c

Battery Pack configuration :

RESULTS

Test 1

· Cell Temperature: Cell 5 oscillates more than cells 4 and 10 due to its fault, reaching higher temperatures.

· SOC: Follows a sinusoidal waveform, reaching values above 100.06 SOC.

· Conduction: Heat flow rate and temperature difference oscillate, with varying thermal conductivity and heat transfer coefficients.

· Convection: Shows heat transfer by convection with varying heat transfer coefficients and thermal conductivity.

· Charge and Discharge Profiles: Current oscillates between -50 to 50 A, and voltage ranges from 30 to 43 volts.

Test 2

· Cell Temperature: Similar trends with cell 5 oscillating more due to its fault.

· SOC: Sinusoidal waveform with consistent SOC values.

· Conduction: Similar trends in heat flow rate and temperature difference.

· Convection: Similar trends in heat transfer coefficients and thermal conductivity.

· Charge and Discharge Profiles: Similar current and voltage ranges.

Test 3

· Cell Temperature: Cell 4 and cell 10 start at 310 K, cell 5 at 320 K. Cell 5 oscillates more due to its fault.

· SOC: Consistent trends with previous tests.

· Conduction: Similar trends in heat flow rate and temperature difference.

· Convection: Similar trends in heat transfer coefficients and thermal conductivity.

· Charge and Discharge Profiles: Consistent current and voltage ranges.

CONCLUSION

1. Temperature differences significantly affect heat flow rate by conduction and convection.

2. Cyclic charge and discharge rates show slight variations due to fixed peak amplitude.

3. SOC remains consistent across different temperatures.

4. Cell 5 shows higher oscillations due to its fault, observable in all graphs.