Design and Analyze a Battery Electric Vehicle with Thermal Management - MATLAB & Simulink
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    Design and Analyze a Battery Electric Vehicle with Thermal Management

    Dr. Lorenzo Nicoletti, Application Engineer, MathWorks

    In recent years, the shift towards sustainable mobility has become a pivotal focus within the automotive sector, largely in response to the stringent emission standards set by European legislation. Among the solutions explored, Battery Electric Vehicles (BEVs) stand out as a viable option for achieving these sustainability goals since they do not cause any local emissions. However, the adoption of BEVs is hampered by concerns over their limited range compared to traditional combustion engine vehicles, making range estimation a critical aspect of BEV development.

    In this presentation you will learn how to build a virtual vehicle model of a BEV designed to estimate range and consumption. The virtual vehicle comprises models for powertrain, driveline, and thermal management. Following a brief presentation of the model, it will be used to highlight the impact of different parameters on vehicle consumption and range.

    Published: 4 Jun 2024

    OK. So now, I first presented like the cell. So now we go one level up, actually a couple of level ups, and we try to simulate an entire vehicle. And we'll try to focus on range and consumption estimation of this vehicle and, also, on thermal management. And again, why is this relevant? Well, I guess most of you are aware of the fact that still we are used to combustion vehicles that have quite a nice range, and we're still not use about an electric vehicle was like 400, 500 kilometer range. That's what they sell. But then maybe on the highways, like 300. So also coming from Munich to Stuttgart with our electric vehicle was a bit tricky. We stopped for a charging break just to be sure.

    So what I will talk about today is, well, first, we'll see how you can improve range of your electric vehicle. What are like the main lever that you could use for this scope? And from that, we will basically derive the requirement of a virtual vehicle model that could be used to estimate your vehicle range.

    And then, I will show how you can build such a model, again, using Simscape. And then, once I presented the model, I will show which results you can get from this model. So that you get an idea of why did I build this whole thing for what purpose?

    So we will see some example. And then I'm sure you're all tired and you want to go for a beer, so then I conclude with a brief summary and outlook and I'll let you go. So let's start with the first part. So why do we need a virtual vehicle for simulating range and consumption? Why do we care at all?

    Well, as already explained actually in the previous presentation, electric vehicle is quite different from combustion vehicle. So we have the energy that's stored in the battery. But then this energy has to go in the form of current to the rest of the powertrain and then move our vehicle. And we will have losses in the motor. We will have losses in the driveline.

    We will have losses because we have people sitting in that car and they also want to stay at a comfortable temperature, not 40 degrees. And we will also have losses due to factors that I cannot control, like the outer temperature or if there is wind against your car, whatever, all these factors together, they make out all the losses that you can have in your vehicle. And each one of these factors is an opportunity to improve range, but at the same time, we have to consider them all at the same time because they all also influence each other.

    So they are opportunity in so every part of the design, but all these parts are all interdependent one another. And as if this wasn't already complex enough, there is another component, which is the thermal management, that adds an additional degrees of complexity. So the reason for that is that in an electric vehicle, our thermal management is very important also to ensure efficiency and safety of the powertrain because the thermal management has to ensure that the battery and the motor are kept at a safe temperature.

    At the same time, if I want to size the thermal management correctly, I also need to know what is the temperature of the motor? What is the temperature of the powertrain? I need to model this component because their losses will define their temperature, so in order to size my thermal management, I need to be able to model these components.

    And that's not the only system that impacts my thermal management. Of course, I have people sitting in the car that want to stay, as I said, at a comfortable temperature. I need to consider that. And depending where I want to sit in my vehicle, I may have different environmental conditions that will have an impact on my thermal management. I also need to consider that.

    And so finally, in the end, there is also the problem that the thermal management is also a system that reduces your range. So we have here a system that influenced by everything, basically, and also impacts my range. So the conclusion is if I want to include all these factors, I need a virtual vehicle model that can model all the components that you see below and the thermal model at the same time.

    And that we can do with Simscape again, as I will try to show in the next five minutes or so. So let's keep it quick. So this is the model that we have built for this purpose. So it's a full virtual vehicle with thermal management. And there are the components that I'm going to briefly present.

    It's going to be quick, and we are going to go through these components so that you have an idea what degrees of complexity this model have. And if you want to find out more, I'm downstairs in the demo area so you can come by and this exact model is there open. So if you want to look at it a bit more in detail, just come by.

    So first of all, we started by building our battery. So we built a battery model. And in this case, we use the product I presented before, Simscape battery, but now we have a bigger battery, so I use simpler model here so that it simulates a bit fast. But also here, I built in a medium sized battery, like I think it was something like 50 kilowatt power.

    We included a charger model so that I can charge my battery when it's empty. I can also simulate this procedure. And we had a cooling plate connected to my battery so that I can monitor the temperature of the battery in the simulation and if needed, I can cool it down or heat it up, depending on the conditions. Then you can see there I have a motor model.

    It's built, again, with Simscape-- in this case, Simscape Driveline. This motor receives a torque request from the driver, and then it will calculate how much current it needs from the battery. We'll take this current and will convert it into torque.

    And then this torque is passed to a gearbox, and then finally to the wheel of my vehicle. Then I need to model the vehicle as well. Again, I can use Simscape Driveline so you can see I have a vehicle body block that accounts for the vehicle mass, its drag coefficient, and all that kind of effect. And I have four tire models that account for the tire losses.

    Also here, I have different level of detail I can use. More complex or less complex tire model will ultimately have also an impact on how fast your model is. Then, since we also wanted to focus on thermal management, I need, first of all, to model the cabin, the passenger compartment, however you want to call it.

    So I have model here with Simscape fluids. So we have a cabin that is represented by volume of air, basically, which is on thermal mass. And then in this cabin, I connect it with some controller that, again, will monitor the temperature. And if it gets too hot or too high, it will activate air flow and it will heat up or cool down the cabin.

    I also take into account that the passenger in the cabin, they create heat, moisture and CO2. We include this as well in the simulation. And I also take into account that my cabin can exchange heat with the environment through conduction convection and there is radiation coming in from the sun, for example.

    So now, I have my cabin. He also needs to get rid of the excess heat, for example. For that, I need a refrigerant loop, which is represented here in blue, is again Simscape fluid. In this case, it's a two-phase fluid that we're using for this kind of simulation. And also here, you can see a snippet of the model.

    Again, this is connected with controller that regulates the refrigerant temperature as needed. And it's refrigerant is driven by a compressor, so I will get rid of the excess heat from the cabin and it will then dissipate it. So then, as I said, then my management task was to ensure that the powertrain stays at a comfortable temperature, let's say, so we built a coolant loop for the motor.

    Again, there is a controller and it checks what the motor temperature is. Our motor will have losses. These losses will increase its temperature, and then if it gets too hot, the coolant loop will take this heat and bring it away from the motor.

    And it can do as follows. There is a pump that basically drives the coolant to the pipe below that you see, this coolant jacket, and then it takes the excess heat from the motor and drives it away. And it can dissipate it, for example, through the radiator up there that is now in the upper right corner.

    And then, last but not least, we also have a battery. We also have to keep the battery at a safe temperature. And for that, we have a separate battery loop, another coolant loop just for the battery. And as you can see here in the battery model, there are these yellow line going in and out. That's the inlet and the outlet of the cooling plate.

    And also here again, we have a controller. We monitor in the simulation, the battery temperature and based on the requirements, we increase the rotational speed of our battery pumps so that there is more or less coolant going in. OK, that was it.

    If you are interested to find out more, come by. I can show you the model. Now let's see what can we do with this model. Is there anything we can get out of it?

    So an example would be, let's suppose, very simple example that we want to go from A to B and we're driving on a highway and it's a very long drive, 700 kilometer. But let's keep it easy. So let's represent here the speed profile over time.

    So we see we drive some time in the simulation. So we will first reach the maximum speed in the highway and we suppose that we keep the speed. Then after 200 kilometer, we do a break to recharge the battery. After 200 kilometer, another break. And then, we go back to the maximum speed, and then there is a third break.

    And then we finish our cycle to the final destination for a total of 700 kilometer. You don't need all these battery breaks. We just wanted to also simulate that when I recharge my battery, it might also get hot. So we also wanted to include these effect.

    You could easily do this also in just two stops. Also important to say, we assume that every time I stop, I stop for exactly half an hour. I try to charge the battery as much as I can. And we assume that outside is a very sunny day with 40 degrees, so we have to keep our cabin, our passenger compartment, at an acceptable temperature, let's say.

    So if I simulate that cycle that we saw before-- so this speed profile in my model as it is seven and a half hour. So if I simulate here, since I have an entire virtual vehicle model, I can represent the result. I can break them down with a bar chart. So I can represent how much energy gets lost, and I can group these energy losses in different components that you can see here.

    So we are driving on the highway, high speed, of course the ergodynamic losses will be the biggest component. So we see that followed by the tire losses. And what I've denoted here for HVAC will be the entire thermal management. So cooling down motor and battery, but also keeping the passenger compartment at an acceptable temperature.

    And we see indeed that it wasn't that bad to include it as a model because it's the third most important component in the losses that we have on our cycle, in this case. Since we have a pretty complex, let's say, thermal model, we can do a further breakdown of these losses and say, which is which one is the main cause of the losses? In this case, is the compressor.

    So we can further break these losses down to the basic components, let's say. This is one way how you can represent the result. Another way, again, if you like to get your hands dirty a bit with Matlab, you can also represent your results as energy flows. So using so-called sankey charts, which is actually the best way to represent this kind of analysis, this kind of energy balance.

    So imagine that the energy that is goes in the vehicle-- for example, the energy that I have at the beginning when the v-battery is fully charged and the energy that I recharge in the vehicle, we represent this in blue. So these are my input.

    This is the energy in kilowatt hour that I put in my vehicle. And then, we have losses, the losses that I've shown before, and we can plot them here as percentage. So how much of the initial and recharge energy has been lost on each component?

    And then, we can also see how much energy I'm left with after 700 kilometer drive that we did. So we see here, we are left with 29.4 kilowatt hour. And then, you could also take this value and knowing the consumption of the previous 700 kilometer, you could estimate how far you could drive or keep driving provided that you follow the same cycle. So these are not a way to represent the results.

    And now that you have a model, again, since we don't have much time, but you can perform a pretty simple sensitivity analysis using your model. So, for example, I simulated this vehicle with assumption that there was only one passenger, the driver. So the results that I just presented in the bar chart, pie chart and the sankey chart was done with one passenger.

    So now I can say, what happens if I have four or five passengers on the same exact cycle? So if I have five passenger, my vehicle is heavier, so the tire consumption will increase. Plus, I have five people sitting in the passenger compartment, so each one of these passenger will generate additional heat, moisture, and CO2.

    And they have to get rid of that, and that will be on the HVAC system. And so I can see the energy at the beginning for the battery is the same because we have the same condition. But we see the driver, when he stop, he recharges more energy because he has lost more energy due to the higher amount of passenger and due to the higher losses that they cause.

    And then, you can also see highlighted that the HVAC losses have indeed increased and the tires losses have increased as well. Please note that it looks like the drag losses, for example, have decreased. The reason is that the percentages are referred to what goes in, so you have more energy going in. So that 49% is exactly the same at 51.7%

    And we also see in the end, we are left with less energy. So I need to recharge more and at the end of the 700 kilometer, I have less energy left in my vehicle. So now, that's one way to represent the result. Some people like some clear numbers, so increasing the passenger from one to five raises consumption by 8.3 kilowatt hour, so you need this much more energy for the same cycle. Or you could say that on average, each additional passenger reduces the maximum range by four kilometers.

    So if you would stop after the simulation and say, how far could I still drive? It would be four kilometers less for each passenger. Or you need to recharge per passenger, 1.9 kilowatt hour more, which, if you how much charging costs on the highway, you could connect it to some cost per passenger if you have this value. So we did some more sensitivity analysis. They are actually published in a paper. So if you're interested for that, just let us know. We can provide you with the link and everything.

    OK. And as promised, I'm already done. So I conclude with the outlook now. So the key takeaway here are I wanted to highlight how you can use Simscape to build actually quite complex, but quite complete virtual vehicle model, also with the thermal management. And I hope it's clear why it would be required to do so. And I hope I could also show that you can use this model to get insights on range consumption.

    And if you have some additional value, you can also get insights on the costs connected to different parameter changes. And one huge advantage of Simscape is that such models are really easy to extend, so you can add more degrees of complexity if what we are providing in this example is not sufficient. What we are providing here, or the entire example I just show, including the simulation I just showed, they are available on GitHub.

    There is the link. So the PDF will be uploaded on the page of the mech in the proceedings. So there is the link. You have access to the entire model 24A and 23B release.

    And of course, the sensitivity analysis I did is quite easy. If you're interested in more complex sensitivity analysis, again, Simulink Design optimization will be the right problem product for that. And if you want to optimize, Optimization Toolbox will definitely be the right product for that. And if you have a lot of variants that you want to simulate and eventually your computer cannot do it anymore, I also took this model, I parallelize it, and I deploy it to a cloud machine.

    So if you're interested in this kind of stuff, you can also come to me. So if you are interested in any of these points, I'll be out there after this presentation. So yeah, and then, I'm done once again. Thank you.

    [APPLAUSE]

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