Battery Pack, Virtual Connection, ANSYS Fluent CFD Simulation

Description

Description

In this project, we present the CFD simulation of the battery pack (4P6S) by Virtual Connection in ANSYS Fluent software.

A battery is a device that converts chemical energy into electric energy through chemical reactions if needed. The main zone of a battery is the active cell, where electrochemical reactions occur. The passive zones include a battery’s positive and negative tabs (terminals) for electric conductivity.

Batteries are exposed to charge and discharge during operation. The electric current is supplied by an external source, during charging. However, an electric load consumes the electric current during discharging.

In Fluent, we can model a single battery or a battery pack. A battery pack is a combination of individual cells connected in parallel or serial for the desired operating voltage and current.

In a parallel configuration, the battery tabs are connected through the same name (positive terminal to the next positive terminal and negative terminal to the next negative terminal). However, in a serial configuration, the battery tabs are connected through the non-same tabs (the positive terminal to the negative terminal and vice versa).

In this project, we simulated 24 cylindrical batteries in series and parallel connections as a battery pack. Our battery pack consists of 6 battery series stages and 4 batteries in parallel per series stage. So, we call the 4P6S battery pack.

Methodology

First, we modeled the battery pack geometry in Design Modeler software. We modeled a battery pack, containing 24 single cylindrical batteries. Each battery consists of a cell zone with positive and negative tab zones.

Then, we meshed the model using ANSYS Meshing software, and 485797 elements were generated.

Finally, we simulated this battery pack using the Battery model in ANSYS Fluent software.

In this project, we used the Multi-Scale Multi-Domain (MSMD) model for battery modeling. The MSMD is a comprehensive method for modeling lithium-ion batteries; because it involves a multi-scale and multi-physic nature.

Then, we used the ECM (Equivalent Circuit Model) sub-model to specify the electrochemical computations. The ECM model is considered a semi-empirical method for electrochemical formulation.

Generally, we consider a real connection for modeling the battery pack. It means we must design several busbars between the terminals of the batteries. However, this causes expensive computation costs, high calculation time, and difficulty in meshing small-scale zones.

Therefore, replacing a virtual connection instead of a real connection is an appropriate idea. It means we use a text file to define the virtual connection.

In this project, we intend to discharge the battery pack at a 5 C rate. For each cell battery, we assume the nominal capacity is 14.6 A.h and the voltage range is 3 v to 4.3 v.

Since the charging/discharging process in the battery system occurs over time, we run the calculation in an unsteady state (transient).

Conclusion

We intend to analyze the battery pack behavior during the discharging process. Therefore, we provided the plot of potential (voltage) variations and maximum temperature variations based on the time.

The results show that when the battery pack is discharging, its overall voltage decreases. On the other hand, due to the battery pack operation, heat is generated and the surface temperature of individual batteries increases.

Then, we obtained the contours of temperature, cell voltage, and SOC (state of charge) at different times. These contours confirm the plots of potential and temperature.