ISSUE WITH SIMULATING BATTERY CELL AFTER PARAMETER ESTIMATION TASK?

Hello,

I have estimated the 2RC equivalent circuit model battery using parameter estimation task. all my updated parameters (SOC,V0,R0,R1, TAU1,R2,TAU2) are of size 21X1 (double). when i am using this parametrized cell with discharger block at 1C discharge(which is for 3600 seconds duration), the results are confusing to me. The cell get discharged completely at 1200 seconds,i.e. reaching to cut off voltage of 2.5V and not showing any effect after it. I am unable to understand what is wrong? Please help.

Thanks,

Sudeep

[Nithin]

Hi @SUDEEP SINGH RAWAT,

It is hard to understand your implementation with the provided data. Could you please share your model or a sample model? This would help me better understand the issue and assist in debugging it.

[SUDEEP SINGH RAWAT]

Hi,

thank you for response. I have shared the screenshot of my cell model with discharger block, scope response, and parameters of cell and discharger block. My battery is of 3Ah capacity. It must get discharged approximately at 3600 seconds, but it is actually discharging completely at 1380 seconds. Please let me know if you can help me with this issue. Thank you.

Answer 1

[Javier Gazzarri]

Hello SUDEEP

Please check the capacity value you entered in the block. If it is lower than the actual capacity then the battery will discharge faster than expected.

Best regards,

Javier

[SUDEEP SINGH RAWAT]

Hello sir,

Thank you for replying. I have checked the capacity value. Its 3Ah, at battery parameter block and the for the discharger block, it is 3A (1C) and cutoff is 2.5V. The discharge cycles completes at 1380 seconds. At 1C, it should complete around 3600 seconds. I am sharing the screenshot of battery 2RC model with discharger block and parameters. Looking forward for your response.

Thank you.

[Javier Gazzarri]

Thank you Sudeep,

I believe this is a combination of the internal resistance and the definition of capacity.

The capacity that needs to be entered in the block is the total capacity, meaning the maximum extractable capacity from the cell. This means at vanishingly small C-rates.

At 1C there is a voltage drop due to i * R, so if the internal resistance is such that OCV - i R reaches 2.5V, the discharge will stop although there is still capacity in the cell. The discharge capacity is alway lower than the total capacity.

What does the current profile looks like? Can you please try to do a constant current discharge at C/30 and see if the capacity discharged is closer to 3Ah?

Best regards,

Javier

[SUDEEP SINGH RAWAT]

Hello sir,

For the 2RC ECM battery model, i have used the estimated values of R,Ro,R1,Tau1,R2 and Tau2, which comes directly from the dynamic discharge test data(18650 Samsung Lithium-ion cell, 3.7V/3Ah). I have attached the image results and simulation vs actual voltage drop after parameter estimation. For the real cell, at 1C, the discharge cycle completes approximately at 3600 under same initial and boundary conditions. i have tried a constant current discharge at C/30 i.e. 0.1A. At this value, the discharge cycle should go up to 10800 seconds(30 hours), but the simulation results shows the cell reached up to 2.584V in 43149 seconds. While the current profile remains constant even after achieving lower voltage threshold, the voltage began to rise up to 4.186V and remained constant until remaining time. What am I missing here? please let me know. i have attached the images for reference.

Thank you.

[Javier Gazzarri]

Hello Sudeep,

Would you kindly send me your Simulink model and the script defining its parameters so I can try it on my side? I am particularly interested in the OCV table you utilized. It seems your OCV is ~2.5V at 60% SOC, which sounds incorrect.

Best regards,

Javier

[SUDEEP SINGH RAWAT]

Hello sir,

Kindly provide your communication email id.

Regards,

Sudeep