Visualization of InterCellThermal connections in battery pack?

Hi,

I have created a 5S5P lithium ion battery pack with cylindrical cells using square topology. I have set the ambient thermal path to "cell based thermal resistance". In the module properties ,it says number of inter cell thermal connections are 20 and number of inter parallel assembly thermal connections are 52. My question is,

1. How these 20 and 52 thermal connections are happening? How can i visualize it? I don't understand the matrix form of the above mentioned connections.
2. How the thermal resistance for each cell is calculated here? I want to model forced air convection. Is the pre set value of 1K/W goes well for my model?
3. How cell level ambient path thermal resistance is set as 25 K/W?How is it different from point number 2?

I have attached the image also for further reference.

Thank you.

Sudeep

Answer 1

[Sebastian Arias Alfaro]

Hello Sudeep,

Please have a look at https://www.mathworks.com/help/simscape-battery/ref/simscape.battery.builder.module.html. As stated in that doc page under InterCellThermalPath: each cell will connect thermally to its neighbor using a simple thermal resistor (or a radiation element). This connection will depend on the battery topology.

1. You can visualize these connections better in the Battery Pack Builder App under the Read-Only Properties for the Module. Please have a look at the image below. The Layout property contains the cell numbering and its useful to help you understand these properties. The InterCellConnectionMapping property shows the "20" inter-cell connections inside all parallel assemblies in your module. The first row of this property contains the list of source nodes, and the second row shows the destination nodes. So, the way you should read it is: Cell 1 in parallel assembly 1 will connect to Cell 2. Cell 2 will connect to Cell 3 and so on. This happens 5 times because you have 5 parallel assemblies inside your module (green numbers in the figure below), giving you a total of 20 connections inside the module. The InterParallelAssemblyCellConnectionsMapping shows the "52" connections that happen between cells from neighboring parallel assemblies. You can read this property in the same way: Cell 1 in parallel assembly 1 connects to Cell 1 of parallel assembly 2. Cell 1 in parallel assembly 1 connects to Cell 2 of parallel assembly 2, and so on...

2. The preset value is just a default, often not suitable for your battery specification. You should calculate this for your specific battery geometry, topology and cell format. 1K/W is probably a very permisive thermal path for a cylindrical cell, so I would advise you calculate or approximate this from first principles equations.

3. As you can see in the picture below, when you select an AmbientThermalPath, the pack builder will add a thermal resistor between the cell and the thermal boundary port. The 25K/W is just a preset default value. You should calculate this for your battery. For cylindrical cells its probably higher than 50 K/W, but this will be a strong function of the design.

Hope this answer helps!