Description

In this project, we present the CFD simulation of the battery pack via 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. During charging, the electric current is supplied by an external source. However, during discharging, the electric current is consumed by an electric load.

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 three prismatic batteries in parallel and serial connections as a battery pack. In other words, we intend to analyze and compare the parallel battery pack (3P1S) and the serial battery pack (1P3S).

Methodology

In this comparison analysis, we simulated two cases: once parallel connections and once serial connections.

First, we modeled the battery geometry via Design Modeler software. The battery construction consists of a cell zone with positive and negative tab zones. In the battery pack, the battery terminals are connected by busbars.

In the first case, we design the busbars in a way that the parallel configuration is modeled, and in the second case, we design the busbars in a way that the serial configuration is modeled.

Then, we meshed the model using ANSYS Meshing software. In the first case, 74240 elements and in the second case, 73216 elements were generated.

Finally, we simulated these two battery pack cases 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.

In both cases, we intend to discharge the battery packs at 10 A current 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 obtained potential (voltage) and current plots based on time for both parallel and serial battery packs.

As shown, in parallel connection, the voltage of all three batteries is the same and the current in the batteries decreases respectively. However, in serial connection, the voltage of the batteries drops in sequence, while the current stabilizes.

In addition, we obtained contours of current magnitude, cell voltage, and passive zone potential for both parallel and series cases. The contours confirm the plots of the potential and current.