Project 2 Thermal modeling of battery pack

OBJECTIVE: 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.

THEORY:

Battery Thermal Management System:

Electric vehicles (EV) develop fast and have become popular due to their zero-emission and high tank-to-wheels efficiency. However, some factors limit the development of the electric vehicle, especially performance, cost, lifetime, and safety of the battery. Therefore, the management of batteries is necessary to reach maximum performance when operating at various conditions.

The battery thermal management system (BTMS) plays a vital role in the control of the battery thermal behavior. The BTMS technologies are air cooling system, liquid cooling system, direct refrigerant cooling system, phase change material (PCM) cooling system, and thermo-electric cooling system as well as heating.

These systems are analyzed through a trade-off between performance, weight, size, cost, reliability, safety, and energy consumption. According to the analysis two prime battery, thermal management systems are recommended: a combined liquid system (CLS) and a variant system with PCM.

The models of CLS and PCM systems were built and simulated using software MATLAB/Simulink. The simulation results predict the battery temperature variation and the energy consumption of BTMS. Through simulating the PCM system model, the effect of PCM on battery temperature variation was investigated and the proper PCM mass was estimated. As seen from the simulation results, BTMS is of great importance to control battery thermal behavior. Further study could be more comprehensive and accurate by combining the simulation mode with battery thermal electric and CFD models.

SIMULINK MODEL:

· In this model we are discharging charging the batteries which are connected in series.

· we measure the temperature dependence of battery by supplying temperature from an external source to the battery.

· connection type is convective heat transfer. As in the real scenario also we don't have conductive heat transfer rather it is convective heat transfer is happening.

· and using a temperature sensor we plot the change in temperature.

· controlled current source gives charge/discharge rate to the battery subsystem.

· current sensor is connected between negative terminal of the battery and controlled current source. current output from current sensor is then integrated and then divided by 3600 to get charge/discharge in coulombs units.

· then output is subtracted from 1 to get state of charge of battery pack. 1 means the battery pack is fully charged.

· voltage sensor is connected across the battery pack to get battery voltage.

Model:

This model is derived from the MATLAB example file "ssc_lithium_battery_with_fault"

Parameters Used:

1) 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.

2) 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.

Sub System

3) 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.

4) Thermal Reference

This block represents a reference point in a thermal network where the temperature is equal to absolute zero.

5) Battery Pack

The workspace file is attached below

Main tab:

Electrical (per cell) Tab:

Thermal (per cell) Tab

Table Break points:

Under Mask

The cell subsystem basically consists 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.

Lithium Cell 1RC subsystem:

This block especially consists of the capacitor (C)value table which depends upon an external physical signal input SOC and T.it is assumed that the capacitor value is varying with the time and hence the equation i=C*DV/dt holds.

Resistance value (R) table depend on external physical signal inputs SOC and T.

Voltage value (EM) implements the cell's main branch voltage source and determines values for capacity(C) and state of charge (SOC).

The defining the equations depends upon cell temperature T.

Thermal Model (Sub system)

Controlled Heat flow rate

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.

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.

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.

Current sensor

The block represents an ideal current sensor, that is, a device that converts current measured in any electrical branch into a physical signal proportional to the current.

Connections + and - are conserving electrical ports through which the sensor is inserted into the circuit. Connection I is a physical signal port that outputs current value.

Cyclic Charge/Discharge Profile

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.

SOC calculation:

For SOC calculation here I used gain block. integrator and sum block sum with PS Simulink converter.

The battery is initially kept at 50%

Gain

Result

For the simulation let use three different temperatures

· 300 K

· 350 K

· 400 K

At 300K:

Pack Temperature

We can see that the pack temperature rises from 293 K to 323 K.

We can see the temperature is higher than the given rate because of the the area of heat transfer is set as 1.01908 m^2 and the heat transfer coefficient is W/(m^2*K).

The temperature of the pack rises slowly over the period of 7000 sec and gets saturated at 323 K

According to charging and discharging of the pack the temperature rises and decreases.

Pack SOC

Initially the SOC of the pack is set to 50%

The Cyclic Charge/Discharge Profile is connected to the pack so the battery can charge and discharge for the period of 7000 sec.

The amplitude is set as 50A, and the frequency is set as 1/ 600 Hz.

The Soc of the pack varies from 50.5% to 50%

Due to the cyclic charging and discharging.

At 350K:

Pack Temperature

We can see that the pack temperature rises from 293 K to 372 K.

We can see the temperature is higher than the given rate because of the the area of heat transfer is set as 1.01908 m^2 and the heat transfer coefficient is W/(m^2*K).

The temperature of the pack rises slowly over the period of 7000 sec and gets saturated at 372 K

According to charging and discharging of the pack the temperature rises and decreases.

Pack SOC

Initially the SOC of the pack is set to 50%

The Cyclic Charge/Discharge Profile is connected to the pack so the battery can charge and discharge for the period of 7000 sec.

The amplitude is set as 50A, and the frequency is set as 1/ 600 Hz.

The Soc of the pack varies from 50.53% to 50%

Due to the cyclic charging and discharging.

At 400K:

Pack Temperature

We can see that the pack temperature rises from 293 K to 422 K.

We can see the temperature is higher than the given rate because of the the area of heat transfer is set as 1.01908 m^2 and the heat transfer coefficient is W/(m^2*K).

The temperature of the pack rises slowly over the period of 7000 sec and gets saturated at 372 K

According to charging and discharging of the pack the temperature rises and decreases.

Pack SOC

Initially the SOC of the pack is set to 50%

The Cyclic Charge/Discharge Profile is connected to the pack so the battery can charge and discharge for the period of 7000 sec.

The amplitude is set. as 50A and the frequency is set as 1/ 600 Hz.

The Soc of the pack varies from 50.54% to 50%

Due to the cyclic charging and discharging.

Comparing the performance of the pack for different temperatures

TEMPERATURE	PLOT	OBSERVATION
300K Vs 350K		Here the SOC of 300K vs 350K is compared We can see that there is slightest difference in the SOC of the pack The 300K pack discharge rate is better than 350K in the rate of 0.0002%
300K Vs 400K		Here the SOC of 300K vs 400K is compared We can see that there is slightest difference in the SOC of the pack The 300K pack charge and discharge rate is better than 400K pack For the charging rate we can see the difference of 0.00007% For the discharging rate we can see the difference of 0.00018%
350K Vs 400K		Here the SOC of 350K vs 400K is compared We can see that there is slightest difference in the SOC of the pack The 350K pack charge and discharge rate is better than 400K pack For the charging rate we can see the difference of 0.00016% For the discharging rate we can see the difference of 0.00012%

CONCLUSION:

From the simulation we observed that due to the thermal changes in battery pack the performance of the pack is affected.

If the pack temperature is kept in ideal temperature, we can get the better battery performance.

___________________________________________________THANK YOU_______________________________________________________