Project 2 Thermal modeling of battery pack

Introduction to Battery Technology for Electric Vehicle - Challenges

Project 2 Thermal modeling of a 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.

Solution:-

To simulate the thermal effects and compare the life cycle performance of a 10-cell series lithium-ion battery pack at various temperatures, charge rates, and discharge rates using MATLAB below Simulink model is created.

PS Constant

The PS Constant block generates a physical signal of a constant value. You specify the value and unit of the signal as the Constant parameter. The constant value is considered the same as Cell capacity AH, so it will be 1C_rate for the battery.

Battery (Table-Based)

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
• Calendar aging

Convective Heat Transfer

The Convective Heat Transfer block represents a heat transfer by convection between two bodies using fluid motion. The transfer is governed by the Newton law of cooling:

Q=k⋅A⋅(TA−TB),

where:

• Q is heat flow.
• k is the convection heat transfer coefficient.
• A is surface area.
• D is the distance between layers (that is, the thickness of the material).
• TA and TB are the temperatures of the two bodies.

Connections A and B are thermal conserving ports associated with the points between which the heat transfer by convection takes place. The block's positive direction is from port A to port B. This means that the heat flow is positive if it flows from A to B.

Temperature Source

The Temperature Source block represents an ideal source of thermal energy that is powerful enough to maintain a 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.

Simulink Model

• The Simulink model is built to simulate the thermal effects and compare life cycle performance at various temperatures, charge & discharge rates in the battery's performance. Therefore, a temperature source (Thermal system) is connected to the Battery system. This temperature source is connected to the battery through Connective Heat Transfer, hence the temperature and the area of contact can vary through them and parallelly the battery performance. 

• 10 table-based battery is connected in series in the below model. SOC port and thermal port are enabled for the battery and are connected to a Scope through a Sum block and the thermal setup consists of a temperature source, Convective Heat transfer, temperature sensor, and a Thermal Reference. 

• A PS Constant block is used as an input current signal for the circuit. It'll act as a c_rate (discharge) for the battery. The constant value of the PS Constant block is considered the same as the battery capacity, hence the discharge will be at 1C_rate. This part is the electrical side of the battery.

• A Controlled Current Source block is connected ib between PS Constant and the battery. This block represents an ideal current source for the battery. An Electrical reference block and a Solver Configuration block are also connected as this model is made using Simscape blocks.

• At the thermal side, all the 10 batteries' thermal ports are connected to a common port signal which is then connected to the thermal system of the model. A Temperature Source block is connected to the thermal port of the battery with the help of a Convective Heat Transfer. It is used to transfer the heat to the battery. Using a temperature source, temperature value can be modified and through Convective Heat Transfer area of contact can be modified, and the impact can be seen in the battery performance.

• A Scope block is connected to both the SOC port and thermal port signals to display the output. PS-Simulink Converter blocks are used to connect Simscape blocks to the Simulink blocks.

• This Simulink model is created to see the Aging efftect of the battery. It will also display the charge and discharge cycle through SOC. It is a simple Simulink Model created using a Square Wave Generatore as an input source, a Contolled Current Source block for the battery.

• A Simulink Battery block is used for this model. Implements a generic battery model for most popular battery types. Temperature and aging (due to cycling) effects can be specified for Lithium-Ion battery type.

• A Bus Selector block is used to get the required elements for the model and are connected to the Scope to display the outputs for the same.

Output

• The below scope output shows the thermal effect to the battery using Thempearture source. Tempearture of the battery is rised for more than 200 degree. This is the battery performance with temperature source when the area of contact is 1e-4. By varying the are of contact, temperature effect will also vary for the battery. As the area of contact increased in the Convective Heat Trasnfer the battery temperature falls down from higher temperature to its default tempearture.

• In this second model scope output, the Aging of the battery can be seen increasing over time. Comparing with the SOC graph, aging graph rises when one charge and discharge cycle is completed and a new one starts and it keeps on increasing over time.