Introduction to Electrical System Modeling | Developing Electrical Systems with Simscape Electrical
From the series: Developing Electrical Systems with Simscape Electrical
Explore the essentials of Simscape Electrical™ and how to model electrical systems with it. An electrical power system with a three-phase circuit and AC/DC converter is developed to demonstrate some essential capabilities of Simscape Electrical for modeling and simulation. You will see how to parametrize the electrical components, change the model fidelity for design requirements, choose the right solver, and leverage Simscape Electrical and Simulink® for electrical power system control design and system-level simulation.
Published: 24 May 2022
Hi, my name is Christine Li, and I'm an Application Engineer at MathWorks. Today we are going to kick off a video series electrical power system and design. This video series will focus on how to use Simscape Electrical for many different electrical power systems and design applications. It will cover microgrid and energy storage. The simulation of switch mode power supply, and some trade offs for electrical system design.
For this video, I'm going to give you an introduction to the electric system modeling with Simscape Electrical. This will be a good start point for those of you who are new to Simscape Electrial and want to do some modeling and simulations. And if you are interested in other topics that we just mentioned, please check the following session in this video series.
OK. So this is our agenda. First, I would give you an overview of the Simscape Electrical, like what is it and why we need it. Next, I would build a model of a simple electrical power system with Simscape Electrial to work with some essentials. And we also will cover the topic like how to choose a software or how to change the model fidelities. Finally, I will share with you some resources and technical support to help you get started.
OK, so we know that there are lots of benefits for the modeling and simulation of electrical power systems. And the very important part here is how to build a model that can meet the requirements. Everyone have different situations. You may know the dynamics of your system really well or you may have no idea of the inside of your system, but you can get some data from it, right? That's why we have multiple methods for the modeling of the dynamic systems from the first principle based to the data driving based.
And as you can see here masterworks has many different tools right but specifically for today's topic, you may already know that Simulink is a graphical based platform for the first principle modeling, which means you generally need to derive the equations to build the model. However, sometimes it may not be realistic for us to derive the equations. It might be very time consuming or we don't know much information about it. That's why the Simscape products can help us.
So Simscape is on the top of Simulink for physical system modeling. It is still based on the first principle modeling methods, but instead of deriving the equation by yourself, it gives you many preview the physical components to build the system much easier and quicker.
So Simscape has preview components for many multiple domains, like electrical, mechanical, thermal, and m but those are very fundamentals right how if we want to do more advanced electrical system modeling. That's where the Simscape electrical can help us.
So Simscape Electrical is one of the extensions from the Simscape fundamental for the electrical power system and design. It provides the components libraries for the modeling and the simulating the electronic, mechatronic, and electrical power systems in close models of semiconductors, motors, and components for applications such as smart grid, renewable energy system, or electromechanical systems.
You can use these components to build your model for many different simulations or analysis, especially if your electrical power system needs to integrate with other domains, such as mechanical, hydronic, thermals, which are all pretty common right? You can use the components from the Simscape fundamental or other add-ons to build the whole system.
Now the highlight is that Simscape give electrical is on the top of Simulink, so you can leverage Matlab and Simulink for a system level design, such as design control rhythms in Simulink willing or do some data analysis in Matlab, especially similar to Matlab Simulink, systems give electrical also support state code generation. So if you're interested in things like real time testing, like hardware in the loop, this is also something you can do with Simscape Electrical.
All right. That's an overview of Simscape electrical. Now let's go to Matlab to see how to use Simscape scale electrical. We will cover three topics. First, I will build a simple model and work you through some Simscape electrical essentials. And then we will talk about how to parameterize or change the model fidelity and how to choose the right solvers.
All right, so this is Matlab, and to get started with the model, we need the first open the Simulink. To open up, we first will see this Simulink star page. Here you can create a blank model or use some templates from the list. You can also access lots of sim examples that can be related to your design.
So some linear resources here that you can access, for example, the Simscape on-ramp can help you get started with Simscape, and also the circuit simulation RAM is in other new courses. You can always get started for with a blank model, but here we can see that Simscape also give you a lot of templates for different domains. Basically, it will have some price settings that is good for this type of applications, and it comes with some essential blocks. So here we will just create a block from the Simscape Electrical templates.
So when we open up this model, we can see that it comes with some initial blocks, like the software configuration block the ground reference signal block, and you need a block to convert Simulink and the Simscape signals, and we have some scope to end the spectrum analyzer to see some results. We also here have some hyperlinks that you can check out, some documentation or the reference.
OK. So now we don't have anything here but I want to build a simple power system. So first step is we can open this Simulink library. So let me just move this window side by side. OK. So when I opens a Simulink library, you can see that we have the similarly fundamental library comes with a lot of blocks that you can use to build your model. But for the Simscape. it also comes with the libraries. So Simscape has its fundamental libraries and some extended ones, like electrical is where we are going to cover today, but also some others.
The fundamental library already gave you a lot of elements that you can use for your design, like electrical. It has some, like a capacitor, diode, resistor, all the stuff that you can build very fundamental or simple electrical systems. But for more advanced design we also need to move to the Simscape electrical library.
So for the Simscape electrical library, we have many subsections that covers like control or semiconductors or passive blocks or even integrated circuits and so on and so forth that you can use. Quick or mention here is Simscape Electrical actually has two main parts, all the stuff here from Simscape electrical call library, but we also have the other part. It's called a specialized power system. And this one is generally used for large power distribution system modeling. This will not be where we are going to cover today. We will be focused on the Simscape Electrical core library.
To get started, we can add a voltage source, right? So I want to add some AC sources. So I can go to the source library. And you can see from the list. We have many things like a battery or other like controlled or non-controlled voltage or current sources, and these are like fuel cells, load flow sources, and more.
So here I would just start from simple. I'm going to just add this very simple voltage source for three phase. After I added it, I can just drag in a job. So let me first adjust to open all the name to keep the block name be there. And then this is a voltage source forever plug when you add it or you may not sure what is it, and what is it and the ports right. How can connect it?
So a really good resource here is, when you double click every block, you can open a documentation from here. When you open the documentation, you can see that it will just give you all the information about this block, like how it has been viewed all the equations under the hood, especially you can navigate to like ports, and then you understand what is this port present for, like is present to a y center. And to the parameterization, every parameter has been explained.
This is documentation, and for this one we will know that the parameters here. It gave me a voltage, and I can serve others but let's now just keep it as default. So I need to first connect this to the ground block. And next after I have this three phase voltage source, I also want to add a load. So I can see here in the passive, I actually have many different types of passive block I can add. I'm going to just add very simple like RLC load. I'm going to just add a three phase RLC three phase block, and I connect it to the network.
So next, after I have this load added, I also want to add a converter to convert the AC to DC. You can go ahead and see that we have this semiconductor and the converter sections. You can go ahead to see that we have some diode GTO or some H bridge or half bridge RGB D MOSFET. You can use all them based on what you need, but here I would just go ahead to go to the converter and pick up the one that I need.
So I have to rectify. There's average one, but we'll use it later, but here let's just use a very regular one. This is rectified for the three phase. So I just drag it and drop to add this rectify and then I can just connect it. Right now I have this DC side. For the DC side, I want to add a resistor. So instead of go to the library to pick it up, if you know the name, a really quick way to add it is on this canvas, any empty places, double click, you can tape the name. And there you will have see that there is some intelligence recommends here, right. You can choose a one, and they're just so connected based on what you learned from your textbook.
OK. And that's it so now I have all the system be connected. I'm going to run the simulation. So I was just going to just change the simulation time to 0.05 seconds, and for the solver here, I would just set up as a solver. We will cover it later, but here I'm going to just use solver by default.
OK. So next, I can run the simulation. Right, as you can see it will compile, and then it will just really quick. After I run the simulation, I definitely want to visualize the results, but how can I do it. So if you are familiar with Simulink, you will know that you can use a scope to just a branch any single node in your model.
But Simscape is a little bit different because it's providing you those physical components. So those are all physical components. You cannot directly drag and to connect it to a scope. Instead, you will you need a sensor to measure any signals you want to measure. I can go to the sensor section. You'll see that we have lots of sensor available for you to use from simple to very advanced one that you can use.
But here I want to pick a very simple one to measure this three phase current and voltage. And here we go, right? So we have this current and the voltage be available. So to add it, I can just drag it and drop, and I want to feed it in here or here. So let me just add it to here. I just need to break this line and connect it.
So now as you can see with the sensor, it will give me two ports, the voltage and the current. So for the voltage, I can connect it to here. It will cover the color line, which is Simscape signal into Simulink that I can use a scope to see that. And for the current, I'm going to stay connected to the spectrum analyzer. And next I can rerun the simulation. I can now have this. So this looks not really good. I can just achieve the sample time to-- leave it small. And here we're going to use one microsecond instead. And let's run the simulation to see the results.
Right so now it's much better. We can see some voltage for three phase being displayed here. And we can also open this spectrum analyzer, and it will show me some frequency domain analyzing results. OK. So that's about how we can use Simscape Electrical block to view the whole system model. And then we can use a scope to visualize that data. We can use a scope but sometimes we go on to monitor many other signals. So use scopes for each of them will make our model look a little bit messy and not very convenient.
So Simscape comes with a logging system that you can use with Simscape explore to analyze all the signals in your circuit. So we can just open the Simscape Task explorer and you can see it listed all the components, you used your model and for each them, it will have some data you can see right. I can double click, it will display on the the right side. This is my current, my voltage, right, and also it has something that has been calculated. And it also comes with a system, that you can convert it to see the results. OK, so that's about the second method to visualize our simulation results.
And sometimes, you may use Simulink as well to view the whole system, so you may have some Simscape data, but also Simulink data as well. So instead of go here and there to check out the results a really convenient way is to use that data inspector, so you can log all the data you want to see. So for example here, I'm going to just a log of this data I can just log it easily from here, and name it as like the APC.
I can also log all the Simscape data that you see in the Simscape explorer in this data use factor. To do so, I'm just going to set up quickly it's in the model settings. We have a Simscape section, so I can record data in the Simulink data inspector, and next I can run the simulation again.
And you can see the existing inspector load some new data. I can open it up. This is all from the model to the data you saw in the scheme export, but this is the data way we have enabled. And we can see that for the Simscape it's all here that you can check it out. So this is a data inspector and we're going to use it more in our later section.
OK good so that's about the first part. Everything essential has been covered. Next is about the model privatization and fidelity. So you can change the model parameters for each of the block just by opening up. There will be something there that you can change from the settings. This is a way to parameterize the system but sometimes, you may want to leverage the fidelity to a more like a detailed model. This is also something that Simscape can support. So you can use Simscape or actually to do a full range of fidelity modeling. And I'm going to use a model here to show you how it works.
So here how I just open the second model, which is about the fidelity comparison. So this is a model that almost is the same as what we just created, but I just added some sensors to each side to mirror the voltage and current. The difference here is about the rectify. What we use before is a regular rectify, and here I also view the same model that changes to an average-value rectify.
So what is the difference of those two? Those are all from Simscape Electrical, but the rectifying block, it can capture those switching effects of the diode. However, the average-value one, it's a little lower fidelity, so it does not capture the switching effects. So we can just run the simulation to see the results. But first let me just go to some initial data that will be needed by this model. And then back to here, we can run a simulation.
And then next step I will just compare the voltage and the current from the two different models to see if there are any difference. I can compare the voltage or current, probably the current. I can click here to open the current. So as you can see, this is current and this it the voltage. For the current, and this is the average current. We have three phase. This is one and we have a Iabc average two and three, which are now the two phases. I will just add the one which is the regular rectify and the same scope and we can just focus on this one.
So we can see that the one with the average-value rectify give you a very small sine wave. However, the one with the regular rectify captures those switching events. So that's a difference, and you can also compare others here. So the main reason that we change the fidelity of the model level is to run efficient simulation to answer some specific are question when you are interested.
For example, the average renewal converters or inverters, they are typically used when we are focused on the system level simulations, but for more detailed converters, like the one we are using here, you will captures the switching events. It also will have a longer simulation time. OK so you can definitely build your model based on where you need.
So that's about changing the model fidelities. And the next topic I want to cover is the solver. We have singled out the solver a little bit in our first part when we build the model, but here I have an example to compare the different solvers and how the solvers will impact our simulation results.
So as you can see here, we have built the same model. The difference is the left side where using all global software which is actually the Simulink solver. And the rice side, we are using Simscape solvers itself to simulate or solve this circuit. For this circuit, it is very simple. We have DC voltage stores connected with a resistor, and we are using voltage to measure the voltage in the network. And this one network has a simple switch that has been controlled by the PWM wave.
And this one we don't have the software to be selected, so we're using Simulink solver and the right side, we check the local solvers settings. So it was just the use of Simscape solver. And then we can run the simulation and compare how it looks like for the PWM and also for voltage.
First, for the PWM waves, we can open it up. It looks pretty close. We don't see any difference. So both solvers can capture those period up and down curves. Let's see the voltage. For the voltage, it's definitely different right? The blue line, which is using the Simulink solver it goes over it can capture those minor steps. However, the yellow line, which the Simscape Local Solver one, it does not capture those precise timing information.
OK, so that's a difference. The reason is actually because here we are using a pretty large sample time for the Simscape Local Solver. To get it better, we can change the sample time. So here, I'm going to use smaller a sample time, which is 1e minus 6, which is a 1 microsecond. When I type it in, it will apply, and I can rerun the simulation in this time. So as you can see, this time is better. The Simscape local solver also can capture the detail the small step information.
So this is a comparison of the sovereign so sovereign is important to simulation, but when you get started and not sure which is good for your studies, you can always keep the local solver unchecked and to try to use the Simulink global solver. And you can see this is the global solver we are currently using. You can open the Settings from there. I'll go to the modeling and settings to choose the one that you can use. You can add this knowledge now and choose a solver, or you can use your own preferred solvers from the list of based on your models. And then you can try your simulation and compare to see if that's what you need.
Just a closing, so the last thing I want to cover is about the control design. So we mentioned in the beginning that Simulink is a client that can use all the tools to fuel your model. And for example, you can use Simulink design control for your power electronic systems, which is a really common use case.
So here this is the example that I would not dive into the detail, but I wanted to show that we have created an AC system and this system with AC/DC converter in telecom. And this has been viewed in Simscape Electrical. And we have some batteries, fuel cells, generators. For example, for the battery converter and the controllers we have some system, but for the control we actually use the Simulink fundamental library to do this period controls.
And you can do more advanced. We have this here we have the AC/DC converter which are pretty similar to what we created in the first step, but this was the active and reactive power control. We actually leverage a Simulink to do the PID control. So this is a really good thing where you can leverage all the tools to build the model and run the simulations for what you need.
All right, now let's back to the slides. So in this video, we introduced the Simscape Electrical and use the demo to show you how we use Simscape Electrical. And finally, I want to share with you some useful resources and MathWorks technical support to help you use this tool.
So we have many different types of engineering support to help you, such as trainings, consulting, and also our technical support. So if you are interested in any of those support, please check out the website for more information. We also have some training, for example, we have the on-ramps which are free training that you can get started with different tools. We also have the paid trainings, and here are some for the Simulink or the control Simscape and state flow. Please check out those links to explore more.
Another very important thing is the shipping examples. So Simscape Electrical has a lot of shipping examples, covering many different applications, and we keeping adding more in each release. So please check out to see if you can find any use for example that is close to your design. Thank you. That's all about the video.