My initial problem is that I have a continuous transfer function which coefficients change with time.
Currently the TF's coefficients are expressed in function of the block mask parameters. These parameters are tunable, and if I change the value in the mask parameters dialog during a simulation the response seems to react appropriately.
However how can I do just that in the code/block flow? Basically, I
have the block parameter 'maskParam' which is set using the mask
parameters dialog, and in the mask initialization commands:
'param=maskParam'. 'param' is used in the transfer function and I
would like to change it in real time (as param=maskParam*f(t)).
I have already looked around and found relevant solutions but either it's unbelievably complicated; or the only transfer function which we are allowed to modify at runtime is discrete and 1) I would like to avoid z-transforming my quite complex TF (I don't have the control toolbox) 2) The sampling time seems to be fixed.. None uses this "dirty" technique of updating parameters, maybe that's the way around?
To illustrate:
I am assuming that you want to change your sim parameters whilst the simulation is running?
A solution is that you run your simulation for inf period and use/change a workspace variable during the simulation period to make the changes take effect.
for Example:
If you look at the w block, you can set it's value in runtime, by doing this:
set_param('my_model_name/w', 'value', 100); % Will change to 100 immediately
You can do similar things with arrays (i.e. a list of coefficients in your case).
HINT FOR YOU
You are using discrete transfer function block. Try the following:
1) Give your block a name e.g. fcn_1
2) In your script, type set_param('your_model_name/fcn_1', 'numerator', '[1 2]'); This will set the numerator value to [1 2]. Do the same for denominator.
3) You should be able to understand, through this exercise, how to handle the property names etc. so that you can change/get them using set_param/get_param.
I leave you to investigate further.
The short answer is that Simulink blocks are not really designed to do this. By definition, a transfer function is Liner-Time Invariant, meaning its characteristics (read coefficients) do not vary with time.
Having said that, there are some workarounds, such as the ones you mentioned in your question. These are the correct way to approach the problem I'm afraid, other than the set_param method suggested by #ha9u63ar. See also this blog on the subject on the MathWorks web site.
Related
I am building a circuit model for a transformer which models the effects of hysteresis. It does so using the Matlab function block on the right, and works successfully when tested in isolation. However, the value of the magnetising inductance Lm depends on calculations requiring the value of Im. But Simulink cannot determine the value of Im without the value of Lm, thus forming an algebraic loop.
However, I have the initial value for the inductance, Lm_initial loaded into the workspace. With this, I should be able to solve for the first Im value, which can be used to determine the next Lm, and so on. However, specifying Lm_initial in the variable inductor's properties doesn't work; Simulink tries to evaluate Lm with the nonexistent 'phi' and 'Im' values rather than trying to solve for an initial Im using the value of the initial inductance.
I have tried solutions involving commenting/uncommenting blocks and implementing further subsystems which activate/deactivate depending on the time step, as well as unit delays, but these run into issues regarding tracking time for calculating the derivatives or output very incorrect/noisy waveforms.
Is there a relatively simple solution for this case? The problem appears as if it'd be relatively simple to solve, but I cannot seem to find a workaround for this.
Transformer Equivalent Model
The exact placement of the unit delay in the loop might be the key here: try to place the unit delay between the [lm] GoTo block and the lm input of your MATLAB function block fcn, that should work. And set the initial condition parameter to Lm_initial.
I am loading my Simulink Model to a microprocessor. After that I want to change a value of a Block parameter.
In the picture below the data comes to Matlab Function block is coming from Serial Port. Now, appearently th incoming data is assigned to input u of Matlab Function block. In that Matlab Function block I want to write a code that changes , for example, coefficient of s in the Transfer Fcn block. Or it can change any other parameter you can give in code hypothetically.
If anybody can give me any solution that would be ver much appreaciated!. Thank you in advance.
Substitute a custom-made subsystem for the transfer function whose parameters have to change, and create the subsystem from basic blocks so that coefficients can be read from signal sources. You might be interested in this
http://blogs.mathworks.com/seth/2011/03/08/how-do-i-change-a-block-parameter-based-on-the-output-of-another-block/
Even if you don't want to change parameters at every time step, the restriction
"[...] calls to set_param also preclude the model from ever being compiled
into a real-time application."
seems relevant to your case.
Anyway, as far as I know the post linked above still applies in 2014.
Hope that helps.
I am doing parameter estimation in matlab using lsqnonlin function.
In my work, I need to plot a graph to show the error in terms of lsqnonlin iteration. So, I need to know which iteration is running at each point of time in lsqnonlin. Could anybody help me how I can extract the iteration number while lsqnonlin is running?
Thanks,
You want to pass it an options parameter setting 'display' to either 'iter' or 'iter-detailed'
http://www.mathworks.com/help/optim/ug/lsqnonlin.html#f265106
Never used it myself, but looking at the help of lsqnonlin, it seems that there is an option to set a custom output function, which gets called during every iteration of the solver. Looking at the specification, it seems that the values optimValues.iteration and optimValues.fval get passed into the function, which is probably the things you are interested in.
You should thus define your own function with the right signature, and depending on your wishes, this function prints it on the command line, makes a plot, saves the intermediate results in a vector, etc. Finally, you need to pass this function as a function handle to the solver: lsqnonlin(..., 'OutputFcn', #your_outputfun).
The simple way to do this would be:
Start with a low number of (maximum) iterations
Get the result
Increase the number of iterations
Get the result
If the maximum iterations is used Go to step 3
This is what I would recommend in most cases when performance is not a big issue.
However, if you cannot afford to do it like this, try edit lsqnonlin and go digging untill you find the point where the number of iterations is found. Then change the function to make sure you store the results you need at that point. (don't forget to change it back afterwards).
The good news is that all relevant files seem to be editable, the bad news is that it is not so clear where you can find the current number of iterations. A quick search led me to fminbnd, but I did not manage to confirm that this is actually used by lsqnonlin.
I am trying to find more information on making a custom PID block in MATLAB. I have most of it done but there are a few parameters that I don't really understand and as such I don't know what value to give them. NOTE I am NOT asking for help tuning PID gains.
They are all inside the filter coefficient block:
When I open the block I have to set a few parameters (output min/max, data type, parameter min/max, etc.). Can someone explain to me what these mean? I can't find good resources anywhere. The only thing that I've tried which works is setting each to [] (i.e. -inf) and the input/output data types to 'Inherit: Inherit via internal rule' but then my output goes to hell. If I copy paste the blocks from the PID block there are a bunch of variables which I haven't defined anywhere so the program won't even compile.
Can someone point out some good resources for this or else explain it? Thanks!
You should get your blocks from the standard Simulink library, not from under the PID block mask. The ones under the mask have been set-up to use variables that are passed from/through the mask, which you are not doing.
The block you have circled is just a gain block (from the Math library).
You most likely won't need to make any changes to the default settings of the block other than the constant value (which needs to be the N that you want to use in the approximation of the derivative term in your controller).
To answer your specific question about what the parameters are, some of them are used to specify data types (if you don't want to use the default double precision), some are only used in code generation, some others only for other specific tasks.
All of them are described (in more, or sometimes less, detail) in the doc for the block, obtained by pressing the help button on the block's dialog.
I often have function such as:
sin(a*w*t + p)
where:
w = natural frequency
t = time
a,p = parameters (which I can vary)
As you can see if you want to vary a,p, you can do so via the standard interface but it's not very convenient. So I thought I'd look for a GUI which has a slider for each parameter. Does such a thing exist?
I've never seen one so I thought I'd quickly write one. However, I'm worried that due to lack of time and knowledge of matlab I will cause problems such as generating too many plot commands when the slider is moved instead of just one. Of course I also have the problem that I want to specify a field where the user can specify the function e.g. by typing sin(a*w*t +p) in a text field and then specify what each variable means which I currently don't know how to do (it looks like a parsing task). Can I do this or should I go with a predefined set of functions?
You can find similar projects in Matlab File Exchange as example.
For instance:
Integral Tool
Function Parameter Slider
I didn't have a look at the code but according to the screenshots, it should help you.
Regarding the function input feature, you can use the function eval (with a few checks on the input if you need reliability). If you want to allow any parametric variable, it may be harder.