Modelling Battery and Calculating Model Parameters

Hello everyone, this is Daniel Esmaili on behalf of Ozen Engineering Corporation. I'm going to talk about modeling batteries and calculating model parameters.

In this presentation, we're going to cover a model, specifically an electric car model as shown here, and the results of tests where the authors were able to calculate the value of elements in this model. This presentation is based on an IEEE paper.

At Ozen Engineering, we solve multidisciplinary engineering problems and have different expertise from engineering professionals and engineers. We have expertise in FEA, CFD, all the way to high and low-frequency electromagnetics. It's also worth noting that we are a light channel pattern of fences.

In this presentation, I'm going to talk about OCV and SOC, the basics. Then I'll talk about charge and discharge profiles, followed by a battery picture. Then I'll discuss the current profile and how OCV is based on SOC. Finally, I'll cover resistor calculation.

Let's start by talking about SOC, which is the state of charge, and OCV, because these are two important parameters for making a battery model. Here, you'll see the scientific definition on the right-hand side, and an icon on the left.

If you find the icon rebellious, that means it was repurposed and is not challenging or demonetized. In one example, the ADATU transacting can be derived from MOXradiosk via this Elliott. Better known as the sweetheart, it's connected here on this side.

If you put meters across the battery, you'll read 1.5 volts, which is the terminal voltage. Here, the ideal battery is also 1.5 volts. When you connect a load, such as an 8-ohm resistor, you'll see the voltage drop. The reason is that there is an internal resistance in the battery.

So, here's the ideal battery, and here's the resistor, which makes the real battery in real life. And then there's a drop in voltage in the internal resistor. That's why you'll see 1.33 volts at the terminal.

So, the terminal and open-circuit voltage are always different unless there's no load connected to the battery, and it's rested for a long time. Now that we know OCV and SoC, let's take a look at the battery.

Here, it's very similar to the battery I showed you earlier, the ideal voltage source along with the internal battery. The point is that the internal battery is a function of SoC, so it means it's not constant. OCV is also a function of SoC.

And it's worth noting that, on top of SoC, temperature is also a big factor. However, in this test, temperature remains constant. So, it's just based on SoC. You'll see the OCV and the internal battery here. However, something is missing here.

If you look around yourself, you'll notice that there are many cases where you left the battery, and the battery died after a long time. This model doesn't represent that. In order to do that, we need to add another item, which is the cell discharge.

Basically, if you leave the battery for a long time, through this resistor, the battery starts discharging or losing its energy and it becomes dead. Now that we know the battery model, let's take a look at the test. On this test, the current is seen in two different phases: charging and discharging.

Here, as you can see, the total charge has dropped about 200 mA. Here, it was charged for one minute, then reset for 10 seconds, charged for one minute, and rested for 10 seconds. That's why you see these two spikes here.

The same pattern is seen here, where it was discharged at 80 amps, reset for 10 seconds, discharged again at 80 amps, reset for 10 seconds, discharged for one minute, and then the test was changed to 30 amps instead of 80 amps.

That's where you see the speed going up again and coming back down all the way here. Once you reach this point, you can no longer take out 30 amps from the battery. It's just that there's not enough power there. However, the SoC is not zero, which means we didn't kill the battery all the way.

In order to do that, the resistor was connected to the battery. That's why you see this jump here. So, it goes up, and the resistor is there, and we give it time. After a while, there is no current at all in the circuit, which means the SoC goes all the way to zero.

Here's the battery, how it looks like. It's a pump, reservoir, and stacks. The size of the battery is equivalent to a vending machine. The test was done on these batteries. Now that we see the battery and the voltage profile, let me show you the current profile.

This is the voltage profile that was shown earlier, and they said you see the current profile. So, it was discharging, charging here, discharged at 80 amps, discharged here at 30 amps, discharged with the resistor, and the same pattern was applied with 150 amps.

That's what you see here, 150 amps, whereas 80 amps here. And again, the same pattern was seen here, where it was discharged at 30 amps. It's discharged here at 30 amps too, and then the resistor is connected to it.

This test was done at different amps and thermal voltage and OCV were measured at different points. So, long story short, if you put OCV based on SOC on different currents, this is how it looks like. As you can see, they are all converging, which means that OCV is converging.

So, there's no need for the OCV to be converging. But then, the ACM is converging. I think that's the point. If you see the OCV, it's converging, which means that no matter what the current is, OCV has the same behavior. There are some who don't see a convergence here.

The reason is that the battery was not rested for a long time. If the battery was rested for much longer than 10 seconds, and if you match a formula on it, this is what you will get.

Here, you see the OCV based on the internal resistance, it's just the basic formula, R multiplied by I equals delta V, so delta V over I will be R, and what is delta V is just open-circuit voltage near the terminal voltage.

We have all this data, so we can calculate the internal resistance, and as you can see, it will give us this profile again. You see convergence here, and the data are scattered at this point.

It's the same reason the material was the same as the previous data, and the data are scattered at this point. It's the same reason the material was not rested for a long time.

If you now have different points, you can fit a curve to the internal resistance, and the only part that is left is self-discharge. For self-discharge, there is also a curve, but the object decided to have a constant number for it, not a function. The number was 5.121 u.

So, we have the self-discharge from the test, the internal resistance, and the open-circuit voltage, and the model is completed with all these numbers. It's only based on SOC, and the temperature is not involved here. The temperature thus remains constant across the whole distance.

We are only changing the loads, and the temperature values used in the data. We have the whole test, and it's good to note that it takes a long time to capture all these data. Each current, for instance, 300, was measured twice to make sure everything is constant and on the same behavior.

So, the battery is modeled here, and we have their parameters. We can use that for analyzing the circuit. Hopefully, this gives you good information. If you have any questions, please do not hesitate to reach out to us.

If you need a design or a consultant for your product, please also feel free to reach out to us. You can reach us at info@ozin.com if you don't like email, you can call us, or you can go to our website, ozininc.com, and see all the products and services that we provide. Have a great day.

Again, this is Daniel Esmaili from Ozen Engineering Corporation.