Project 2 Thermal modeling of battery pack
Q: 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.
Ans:
AIM: To develop the 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.
Introduction:
The performance and life-cycle costs of electric vehicles (EV) and hybrid electric vehicles (HEV) depend inherently on energy storage systems such as batteries. Battery pack performance directly affects the all-electric range, power for acceleration, fuel economy, and charge acceptance during energy recovery from regenerative braking. Because the battery pack's cost, durability, and life also affect the cost and reliability of the vehicle, any parameter that affects the battery pack must be optimized.
Temperature and temperature uniformity has a strong influence on battery pack performance and consequently, that of HEVs and EVs. All the modules in the pack should be operated within the optimum temperature range suitable for the particular electrochemical couple used. In addition, the uneven temperature distribution in a pack leads to different charge/discharge behavior that results in unbalanced modules and reduced pack performance. Because HEV batteries have high specific power and undergo aggressive HEV charging/discharging profiles, thermal issues in an HEV pack are of more concern than in EV packs.
Simulink Model:
the blocks present inside the systems are,
Thermal Reference
Reference connection for thermal ports
Library:
Thermal Elements
Description:
The Thermal Reference block represents a thermal reference point, that is, a point with an absolute zero temperature, concerning which all the temperatures in the system are determined.
Temperature Sensor
Description
The Temperature Sensor block represents an ideal temperature sensor, that is, a device that determines the temperature differential measured between two points without drawing any heat.
Connections A and B are thermal conserving ports that connect to the two points where temperature is being monitored. Port T is a physical signal port that outputs the temperature differential value.
The block positive direction is from port A to port B. The measured temperature is determined as T = TA – TB.
Ports
The block has the following ports:
A
Thermal conserving port associated with the sensor positive probe.
B
Thermal conserving port associated with the sensor negative probe.
T
Physical signal output port for temperature.
Battery (Table-Based)
Description
The Battery (Table-Based) block represents a high-fidelity battery model. The block calculates no-load voltage as a function of charge level and optional temperature using lookup tables and includes several modeling options:
Self-discharge
Battery fade
Charge dynamics
Temperature Source
A constant source of thermal energy, characterized by temperature expand all in page
Description
The Temperature Source block represents an ideal source of thermal energy that is powerful enough to maintain specified temperature at its outlet regardless of the heat flow consumed by the system.
The source generates constant absolute temperature, defined by the Temperature parameter value.
Convective Heat Transfer
Description
The Convective Heat Transfer block represents a heat transfer by convection between two bodies by means of fluid motion. The transfer is governed by the Newton law of cooling and is described with the following equation:
where
Q Heat flow
k Convection heat transfer coefficient
A Surface area
TA,TB Temperatures of the bodies
Connections A and B are thermal conserving ports associated with the points between which the heat transfer by convection takes place. The block positive direction is from port A to port B. This means that the heat flow is positive if it flows from A to B.
controlled current source:
controlled current source is used to know the flow current in the circuit. for that we added a controlled current source. it get the input from the ps constant, when the PS constant triggers the controlled current source at that time we will see the results.
PS-Simulink converter
The PS-Simulink Converter block converts a physical signal into a Simulink output signal. Use this block to connect outputs of a Physical Network diagram to Simulink scopes or other Simulink blocks.
Conductive Heat Transfer:
The Conductive Heat Transfer block represents a heat transfer by conduction between two layers of the same material. The transfer is governed by the Fourier law and is described with the following equation:
Q=k·AD(TA−TB)
where
| Q | Heat flow |
| k | Material thermal conductivity |
| A | Area normal to the heat flow direction |
| D | Distance between layers (thickness of material) |
| TA,TB | Temperatures of the layers |
Connections A and B are thermal conserving ports associated with material layers. The block positive direction is from port A to port B. This means that the heat flow is positive if it flows from A to B.
Signal Builder Block:
Signal builder block used to create the desired input signal with respect to the simulation time
Signal builder block is used to give an a input to drive the vehicle at a given range
Based on this drive cycle data the battery will discharge.
About the model:
- In this module, we used the 10 table-based battery block in which we used here default values of current and voltages. here I put the initial temperature value is 293K etc. and these 10 table-based battery cells are connected in series.
- Also here we use the conductive heat transfer block in which we put the thermal conductivity is 401 W/(K*m), the area is 10 m^2, and the thickness is 0.1m.
- here we use the convective heat transfer block in which put the heat transfer coefficient is 20 W/(K*m^2), and the area is 10 m^2. And one end of this block is connected to thermal source and the other is connected to a particular cell.
- here we use perfect insulators also.
- he i put the value of the temperature value is 293.15K (equal to 20°C)
- here we use a temperature sensor to sense the temperature of the cell and display the value in the scope and dashboard. Also, one end is connected to the thermal reference.
- and SOC of every cell is also calculated by using add and gain block and displaying the soc value in % in the display block.
- Here we have to change the convection heat transfer block parameters and also compare the results of soc and current and voltages, and also give an a charging at regenerative breaking and discharging of the battery.
Temperature converted from degree Celsius to kelvin
Example: AT 25°C
CASE-1: AT 20°C and AT Convective Heat Transfer area is 10m^2
Results:
Graph for State of charge (SOC) and Temparature of the battery pack:
AT 20°C
In the above graph based on the drive cycle input the battery will discharge and also we found some spickes in the SOC. that is looks the battery pack is charging due to regenerative braking. And the battery will discharge at end of the drive cycle time is nearly equal to 94 percentage At the temparature is 20°C (298.15K). And the temparature is gradually increasses from 293 to 293.15 after that the temperature is remains constant till the end of the Drive Cycle. The time period of the Drive cycle is nearly 1400 sec.
Current and Voltage graph:
Current is increasses and decreasses with respected to based on the Drive Cycle input and in the graph the current is increases with decreasses with voltage.
Indiviual cell SOC Graph:
All indiviual battery cells are discharging looks same or similar. All the battery cells are discharge with given input Drive Cycles.
CASE-2: AT 45°C and AT Convective Heat Transfer area is 10m^2
Results:
Graph for State of charge (SOC) and Temparature of the battery pack:
AT 45°C
In the above graph based on the drive cycle input the battery will discharge and also we found some spickes in the SOC. that is looks the battery pack is charging due to regenerative braking. And the battery will discharge at end of the drive cycle time is nearly equal to 87 percentage At the temparature is 45°C (318.15K). And the temparature is gradually increasses from 293 to 318.2K after that the teamparature is remains constant till the end of the Drive Cycle.Compare to previous test case if the temperature increses the battery will state of charge will decresses. The time period of the Drive cycle is nearly 1400 sec.
Current and Voltage graph:
Current is increasses and decreasses with respected to based on the Drive Cycle input and in the graph the current is increases with decreasses with voltage.
Indiviual cell SOC Graph:
All indiviual battery cells are discharging looks same or similar. All the battery cells are discharge with given input Drive Cycles. every cell has discharge the energy nearly 87% of cell soc.
conclusion:
In this model i will observe that the battey state of charge is discharged more when the temparature of the battery pack increases.