I should stimulate how the lowpass filter work exactly with simulink so i create a signal generator f=50 hz and i make a lowerfilter and after that i want to see it so the only tool that i found it is spectrum analyzer but when i simulate i get two errors
Sorry if it's not really explain because i'm beginner in simulink
The signals being fed into the Spectrum Scope blocks need to be discrete-time signals instead of continuous-time. You can accomplish this by adding a Zero-Order Hold block before each Spectrum Scope, setting the desired discrete sample time in the Zero-Order Hold block's dialog parameters.
As a heads up, you're probably going to want to buffer your signals as well (the spectrum is calculated on "frames" of data, which you can read about here: Create Frame-Based Signals). To do this, you can either use a Buffer block in between your Zero-Order Hold and Spectrum Scope, or select "Buffer Input" in the Spectrum Scope dialog parameters.
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For example, I have a controller consisting of integrator and sine web signal combined in the input. My question may be very naive to you, please help me to understand.
In the picture I have a frequency which is the input of an integrator then two cos and sine block. How to make each Simulink block discrete using ZOH and rate transition block in Simulink.
Two potential solutions
Change the sample time of the sinewave to something that is non-zero. This will make it a discrete signal
Use a Zero Order Hold (as you've mentioned) to convert the signal to discrete, you will need to specify a sample time for this block to perform the conversion. Setting the time to 0.5 will sample the signal every half second for example.
I build an equivalent circuit in Simulink and it works. Now I want to get the nquvist plot of this equivalent circuit. Does anyone have an idea how to achieve this. Till now I only get the Impedance versus the frequency. I attached the equivalent circuit:
Thanks a lot
When using blocks from "Simscape Power Systems Specialized Technology" use voltage/current measurement blocks (depending on the numerator/denumerator of the transfer function). The outputs of these blocks are Simulink signals. Once you have the signals, you can use the "Simulink Control Design" toolbox to display a Nyquist plot directly. See following link for an example (although for Bode plot, but it is straight forward to apply the procedure to Nyquist plots).
I want to be able to externally have inputs for the lower passband edge frequency and higher passband edge frequencies for the butterworth filter block in the simulink signal processing toolbox in matlab. How can I achieve this. Currently you'll have to click the block to specify these frequencies and this is not possible at runtime.
Regards,
Alfred
Basically you are asking for a filter that has time varying parameters. The Butterworth filter block does not allow for this, and cannot be modified to do so, so you are going to have to roll your own. This can be achieved in several ways:
Determining the difference equations that you need to implement, then creating a filter out of fundamental blocks (product, summation and unit delay blocks) where the "parameters" you want to change are fed into the product blocks as signals.
Using a block such as Transfer Fcn Direct Form II Time Varying. (This assumes you can parameterize the changes you need as a gain-scheduled signal.)
Write an S-Function (or perhaps a MATLAB Function block) to implement any detailed/specific functionality.
I believe I am doing something fundamentally wrong when trying to import and test a transfer function in Simulink which was created within the System Identification Toolbox (SIT).
To give a simple example of what I am doing.
I have an input which is an offset sinusoidal wave from 12 seconds to 25 seconds with an amplitude of 1 and a frequency of 1.5rad/s which gives a measured output.
I have used SIT to create a simple 2 pole 1 zero transfer function which gives the following agreement:
I have then tried to import this transfer function into Simulink for investigation in the following configuration which has a sinusoidal input of frequency 1.5rad/s and a starting t=12. The LTI system block refers to the transfer function variable within the workspace:
When I run this simulation for 13 seconds the input to the block is as expected but the post transfer function signal shows little agreement with what would be expected and is an order of magnitude out.
pre:
post:
Could someone give any insight into where I am going wrong and why the output from the tf in simulink shows little resemblance to the model output displayed in the SIT. I have a basic grasp of control theory but I am struggling to make sense of this.
This could be due to different initial conditions used in SimuLink and the SI Toolbox, the latter should estimate initial conditions with the model, while Simulink does nothing special with initial conditions unless you specify them yourself.
To me it seems that your original signals are in periodic regime, since your output looks almost like a sine wave as well. In periodic regime, initial conditions have little effect. You can verify my assumption by simulating your model for a longer amount of time: if at the end, your signal reaches the right amplitude and phase lag as in your data, you will know that the initial conditions were wrong.
In any case, you can get the estimated initial state from the toolbox, I think using the InitialState property of the resulting object.
Another thing that might go wrong, is the time discretization that you use in Simulink in case you estimated a continuous time model (one in the Laplace variable s, not in z or q).
edit: In that case I would recommend you check what Simulink uses to discretize your CT model, by using c2d in MATLAB and a setup like the one below in Simulink. In MATLAB you can also "simulate" the response to a CT model using lsim, where you have to specify a discretization method.
This set-up allows you to load in a CT model and a discretized variant (in this case a state-space representation). By comparing the signals, you can see whether the discretization method you use is the same one that SimuLink uses (this depends on the integration method you set in the settings).
I'm running a SimEvents simulation using Variable-step discrete solver. I save a signal data using a 'to Workspace' block, but the plot that I obtain is different from the one shown in the 'Scope' block inside the model.
The original signal remains constant between t=64[h] and t=65.4[h] (and this seems to be correctly done also in the matlab plot), while elsewhere it is like the plot command and the 'scope' block are working with different "sample times".
I'd like to obtain a plot showing the typical "step shape" of a discrete signal rather than a "nearly continuous" signal.
I've used the Scope 'save data to workspace' as well, but I didn't solve the problem.
I would have attached some screenshots in order to make the question more complete, but this is my first question so I have not enough reputation to post images. If you need, I can send them to you via e-mail.
Thank you in advance!
There are no screenshots to look at, but my guess would be that the signal is discrete, and the Simulink scope block, knowing this, is only changing at the discrete time points.
However, if you are plotting the data dumped to MATLAB using the standard plot function then it treats the data as continuous and joins successive points with a (non-constant) line.
If that's the case, you most likely want to be using the stairs function to do your MATLAB plottig.