I want to feed the initial conditions in state space matrix block in simulink by using signals "from-go to signal blocks". I m trying it with signal blocks but some errors pop up at the end and it says that the signal variables used as initial conditions are all undefined variable. In other words there exists "Undefined function or variable".
Any help appreciated, thank you
I take it you are using the State-Space block. The "initial conditions" parameter for the block is just that, a parameter:
You need to understand the difference between a parameter and a signal: a parameter is something that is constant throughout the simulation (e.g. a variable in the MATLAB workspace), whereas a signal is something whose value is updated at each time step. You cannot use a "signal" to parameterise a block, it's not possible, you can only use a parameter. Hope that clears things up.
If I misunderstood your question, please provide more details, including which block(s) you are using and if possible a screenshot of the model and the relevant block parameters.
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.
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.
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 have a constant block in a simulink model; i would like to change its value during the simulation when a particular event occurred in a stateflow chart. how can i do it?
If the Stateflow chart output indicates when this event has occurred, or if you can add an additional output that toggles when the event occurs, loop this indicator back (possibly through a Unit Delay block) to the control input of Switch block. The two inputs to the Switch would be two Constant blocks containing the two different values.
If you must do this programmatically without modifying the model, take a look at the reference for the sim command. I should warn you that this may not be trivial to accomplish.
Also, if want to be able to modify the contents of a Constant block mid-simulation (i.e. make it tunable), you may have to turn off Simulink's optimization settings that inline invariant parameters.
You can also add a Slider Gain block between your constant block and the Stateflow block. This would allow you to change the value of the slider gain block during simulation, without the need to change the value of the constant block.
I have 2 embedded Matlab functions which I am using to create a Simulink model. Both functions use the output of the second function as their input. I am getting an error at the moment indicating that this is an invalid loop.
Does anyone know how to implement this type of behaviour?
You've created an algebraic loop, which means that to compute the inputs of the Embedded MATLAB block are directly dependent on the outputs of the block. This is not allowed when the loop is a "self-loop", i.e. there is only one block in the loop.
One way to fix this is to put Unit Delay block(s) somewhere on the signal feeding back into the Embedded MATLAB block. See the documentation on algebraic loops for more information.