Microgrid System Overview | Evaluating Microgrid Control with Simscape Electrical, Part 1
From the series: Evaluating Microgrid Control with Simscape Electrical
Patrice Brunelle, Hydro Quebec
Graham Dudgeon, MathWorks
Modeling and simulation are invaluable tools for supporting the development of electrical technology. Attention must be given to choosing an appropriate level of fidelity in the system-level model in order to effectively support the execution of specific engineering tasks. A microgrid system which facilitates functional evaluation of the operational response of different microgrid control modes is described, and instructions on how to download the model from File Exchange are given.
Published: 12 Jun 2022
Here is the system that we'll be exploring today. It's a microgrid with a PV array, a battery energy storage system that I will call BESS, and a load. The microgrid can operate in islanded mode or be connected to the main utility grid. Our objective is to evaluate the functional correctness of the various control mode through simulation of appropriate operational scenarios.
Note that you can find a version of this model on MathWorks File Exchange, by searching for Microgrid Dynamic Operation. It's an entry by my colleague, Pierre Giroux, Quebec. And if you download this model, you will be able to explore and simulate all the operational scenarios that we'll be discussing today.
All right, so when we're in Google, what we do is, we take File Exchange, and then click on MATLAB Central MathWorks. And once we're in here, we've got access to all the community files that exist for the MathWorks community. So I'm going to take Microgrid Dynamic Operation. [AUDIO OUT] --there's a number of other microgrid entries here, by other members of the community.
But Microgrid Dynamic Operation, it's this one here by Pierre Giroux. So you click on that, and then you just click Download. And if you click Download, what will happen is, you will get a zip file which you can then unpackage. And then you can get up and running and do everything that you're going to be seeing in this webinar today.
Let's take a look at the battery storage system in this whole. The battery energy storage system is a 1-megawatt 1-megawatt hour, lithium-ion system. It's connected to a two level converter. The converter is modeled at a fidelity level known as switching function, meaning that the individual switches are not modeled and the PWM signals are averaged over the simulation's handle time.
This means we can maintain as much harmonic information as possible. BESS control can switch between grid forming, grid following, grid synchronization, and imbalance compensation, depending on the operational mode of the microgrid. With the switching function fidelity level, we use a pulse averaging PWM generator.
So what do we mean by that? Here you see a PWM signal that has been generated from a 300 hertz carrier wave and a 60 hertz modulation wave. If my simple time is, say, 1 over 600, hertz indicated by the dashed line, you can see that I do not have an appropriate resolution to accurately capture the pulse transition.
What we do with pulse averaging is, we calculate the ratio of the pulse on time, divided by the sample time. And that average value is then used in our next sample time. With this pulse averaging generator, and the corresponding switching function converter model, a much higher sample time can be used for the model while maintaining a high-fidelity simulation.
Here we can see the array of control system we have implemented for the battery energy storage system. We won't spend time in this webinar looking in detail at the implementation of these controls subsystem. But we would encourage you to download the model from File Exchange, so you may explore these subsystems in more detail, at your leisure. We will, however, be describing the operational mode and show the simulation result in order to discuss the operational behavior we are seeing.
The solar power plant is a 1-megawatt rated system that is connected through a boost converter and three-level converter. The boost converter controls the power output of the solar panel in this model as average model. This means that the duty cycle is fed directly into the converter and the output voltage as load switching harmonics. The two-level converter is a switching function model of the same fidelity level as the BESS two-level converter. PV control can switch between maximum power tracking-- we used to say MPPT-- and power curtailment, depending on the operational mode of the microgrid.
The load-- the load is a simple impedance with active and reactive power specify. We can connect and disconnect load number two to provide load shedding and load connection, as appropriate. The utility grid is configured as a 120-kV to 25-kilovolt system. Connection to the microgrid is made through a 25-kilovolt, 600-volt transformer. The utility grid has a single-phase load on phase C at the primary of the microgrid transformer. It can be connected to close a system imbalance. That completes our brief tour of the system architecture.