I have a simulink model of a control system where a output is being constantly compared with the setpoint and error is being set to the controller. I use a matlab file to call this model and send disturbance. I want to optimize a parameter that affects the value of the controller gains on the basis of the error (i.e., to reduce error). How to use GA to call this simulink file and set parameter at each iteration.
I took help from this link: "https://in.mathworks.com/matlabcentral/answers/343672-how-could-i-connect-simulink-model-to-the-genetic-algorithm-toolbox"
but it is showing error:
"Exiting due to infeasibility: 1 lower range(s) exceeds the corresponding upper range."
I have exactly the same problem, but in your case, the error that appears is referred to problems of value of the design variables that exceed the upper/lower boundary level defined in the genetic algorithm.
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 had as primary objective to make a controller for the transfer function (5.551* s^2), using root locus I made the controller shown below. Analyzing the step response in the Workspace using the step () function I had a satisfactory answer but when I try to transfer this answer to Simulink the response behaves differently, at steady state for example I wish to have the smallest possible error as it was obtained in Workspace but in Simulink there is a big error and for some reason at 8 seconds time (Simulink simulation time) there is a "jump" as shown on the display and when I change the simulation time there is a change in this "jump" too and I do not know why these changes between one environment and another.
Step response in Workspace
Step response in Simulink with 8s of simulation
Step response in Simulink with 12s of simulation
Simulink controller
Simulink transfer function
I expected to make a controller that has an error less than 5% and an overshoot smaller than 25%, so I first made a controller with two integrators to nullify the effects of zeros on the source, after that I added two more integrators on the source to try decrease the error, the zero at -0.652 I used the angular condition for this and the gain of 0.240251 I used the modular condition.
I wasn't expecting the most optimized behavior possible, just that it has minimum conditions that satisfy the imposed conditions, so I didn't worry for example about the four integrators at the source.
I tried use the sisotool() command thinking that I had done something wrong, but the result changed a lot when I was simulating Simulink so I discarded this option and kept the controller I made using root locus.
Your MATLAB code and your Simulink model are not the same, and hence the different results.
MATLAB allows you to define the non-causal plant model P_ball, then form the causal closed loop CL, which can have its step response generated.
Simulink does not allow you to model non-causal blocks (even if the overall model is causal) and hence will not allow you to implement s^2, which I assume is why you have used two differentiation blocks. But a numerical differentiation is not the same as a Laplace s operator.
You would have to make the plant causal by incorporating two poles that are large enough to not adversely effect the overall simulation. So your plant model needs to be something like 5.551*s^2/((s/1000 + 1)(s/1000 + 1)) which can be implemented using a Transfer Function block with a numerator of 5.551*1000*1000*[1 0 0] and a denominator of [1 2*1000 1000*1000].
Alternatively you could just implement PID * P_ball (where you manually do the 2 zero/pole cancellations) which is causal.
I've had to create the Simulink Diagram after this picture:
My answer is this one:
I've gave some values to a, b and c (like 3, 4 and 5), but when I try to run it, it gives me the following warning:
Warning: The model 'ex2_2' does not have continuous states, hence Simulink is using the
solver 'VariableStepDiscrete' instead of solver 'ode45'. You can disable this diagnostic by
explicitly specifying a discrete solver in the solver tab of the Configuration Parameters
dialog, or by setting the 'Automatic solver parameter selection' diagnostic to 'none' in the
Diagnostics tab of the Configuration Parameters dialog
Warning: 'ex2_2/Unit Delay' is discrete, yet is inheriting a continuous sample time; consider
replacing unit delay with a memory block. When a unit delay block inherits continuous sample
time, its behavior is the same as the memory block. Unit delay block's time delay will not be
fixed and could change with each time step. This might be unexpected behavior. Normally, a
unit delay block uses discrete sample time. You can disable this diagnostic by setting the
'Discrete used as continuous' diagnostic to 'none' in the Sample Time group on the
Diagnostics pane of the Configuration Parameters dialog box. "
and the output (scope) it's just a step signal...
I don't know where I'm wrong here.
You've built the model correctly, but did not configure it correctly.
When running the model as-is, what will happen is the following:
The Step block is a continuous-time source by default (it's Sample Time setting is 0).
Simulink sees that the Step is connected to the Unit delay block, which is guaranteed to have constant output during minor steps (unlike Memory blocks)
According to the documentation on sample times:
[...] Simulink sets [Fixed-in-Minor step] as either an inherited sample time or as an alteration to a user specification of 0 (continuous). This setting is equivalent to, and therefore converted to, the fastest discrete rate when you use a fixed-step solver.
Continuous sample time degrades to Fixed-in-Minor-Step rather than Discrete-time in the context of Variable-step solvers. Variable step size is used to speed up simulations (larger steps are taken when accuracy allows it), but requires trickery to compute, for example, the exact time at which the step triggers (the "Enable zero-crossing detection" tick box in the Step block's options). So, Simulink's best way forward in this particular situation is to convert the sample time of the Step block into Fixed-in-Minor-Step, which is propagated forward and inherited by all other blocks in the model.
This is usually an awkward type of sample time, which is effectively not continuous-time, but still seen by all blocks as such. Therefore, the inherently discrete-time Unit delay will complain about being driven by a continuous-time signal (your 2nd warning), and Simulink itself will complain about the complete lack of "real" continuous-time blocks anywhere, while being instructed to use a continuous-time solver, ode45 (your 1st warning).
As usual in software development: it's always best to be explicit, about everything. In this case, the simplest way out of this is to explicitly specify a discrete-time, fixed-step solver in the model configuration dialog. That way, the continuous-time from the step will be automatically converted into discrete-time for the Unit delay.
The block diagram you want to implement is a discrete-time system. Since there are no Ordinary Differential Equations (ODE) but only their discrete counterpart (Finite-differences equations), you do not need an ODE solver as the warning 1 points out.
In discrete-time systems you have to specify your sample time in order to approach to a continuous-time representation where every single instant t is built up by the discrete integer n and its progressions (n+1, n+2, and so on) as t = nT where T is your sample time; Simulink basically expects that you respect this kind of logic, then asks for a sample time. By default Simulink sets it variable which may lead the result "out of track". This is what the warning 2 points out.
Solution: In the 'Model Configuration Parameters' menu, at the Solver tab, set 'Fixed-Step' as Type. The pane will change with a field related to the sample-time (Fixed-step size); set then a Sample time in seconds different than "auto" (e.g. 0.01). This will solve the warning 2. Still in the Solver menu, set also 'Discrete (no continuous states)' instead of any other useless solver. This will solve the warning 1.
What is a test point and its intended use in matlab ?
I am working on a model and have to use 3 AND gates in conjunction coupled with similar 2 more AND gates. While checking the model I am getting warning "Identify single logical operator blocks with more than 9 inputs signals.", which is not shown if I use testpoint on each of these AND gate output.
Think of a signal in Simulink as corresponding to a memory location.
In an effort to reduce memory consumption, one of the standard optimizations used by Simulink is to re-use the same memory address when possible.
For instance, assume the input to a gain block is stored at memory location X. Then the output of the gain block would overwrite the data in X. Consequently the input value would no longer be available. But it doesn't need to be as it's value is never used again. (This assumes that the input value is not used elsewhere, such as feeding a block like a Scope.)
In your case, the warning is telling you something about Simulink storing the logical values in memory locations that it subsequently overwrites when possible.
Note that Simulink will never re-use memory when it needs the signal value in subsequent calculations, i.e. when it would effect the simulation result if it did so.
Nor will it re-use memory (for a specific signal) when you designate the signal as being a test point.
This is why the warning is going away in your case.
One particular use of a test point is if you are using a Floating Scope. Floating Scopes cannot be made to look at signals where the memory is being re-used because then it wouldn't be clear which signal was being displaying.
By looking at only test points it is guaranteed that you are looking at the expected data/memory.
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.