I have a block diagram in Simulink where one of the blocks is gain and depends on time.
How can I set the gain to change according to the simulation time?
I tried to use clock block, send the variable to workspace and then set it back to gain parameter however its not working.
mdl_name='HW3_Q1_Sim';
open_system(mdl_name);
a = sim('HW3_Q1_Sim','SimulationMode','normal');
SimTime = a.get('SimTime');
x = SimTime^2;
set_param([mdl_name,'/Gain1'],'Gain',x);
Any tips please?
Use the following blocks:
Math function block (set to "square")
Clock block
Product block
Arranged in that manner:
Related
I'm a super beginner in Simulink models and control systems.
I have .slx Simulink model for drone dynamics system.
It takes in two inputs (roll cmd, pitch cmd) and outputs velocity x, velocity y, position x, and position y.
From here, it seems like I can open the system by calling
open_system('myModel.slx', 'loadable');
But how do I put inputs and get output values?
Is there a way I can do this in a gui?
EDIT:
Here is the full layout of my model:
When I did
roll_CMD=10;
pitch_CMD=20;
I got a warning saying:
Input port 1 of 'SimpleDroneDynamics/...' is not connected.
How do I feed inputs using port numbers?
How do I get outputs with port numbers? I tried
[vx, vy, px, py] = sim('SimpleDroneDynamics.slx');
and got an error saying
Number of left-hand side argument doesn't match block diagram...
Is there a way to continuously feed inputs at every time step? This being controller module, I think I'm supposed to feed in different values based on output position and velocity.
EDIT2:
I'm using Matlab2017a
About the first two points of your question:
In simulink:
For the inputs you can use a constant block and when you double click the input block you can assign a value, which can be a workspace variable.
To get the outputs to your workspace you can use the simout block (make sure to put Save format to array).
Connect inputs to your simulink model
Connect outputs of your simulink model to the simout blocks.
MATLAB script
clc;
clear all;
roll = 10;
pitch = 20;
sim('/path_to_simulinkmodel.slx')
time = simout(:,1);
velocity_X = simout(:,2);
velocity_Y = simout(:,3);
position_X = simout(:,4);
position_Y = simout(:,5);
About the third point of your question
You can define the duration of your simulation in the block diagram editor. You can put a variable which is defined in the calling script. There are multiple ways of achieving time dependent input variables:
One option I personally don't recommend is using a for-loop and calling the simulink model with a different value of roll and pitch
for i = 1:numberOfTimesteps
roll = ...
...
sim('simulinkModel.slx')
end
A second and more efficient approach is changing the constant blocks to other source blocks like ramp signals or sinusoid signals
First of all Simulink model use main Matlab workspace. So you can change your variables values at command window (or just at your script) and run Simulink model.
There are several ways to initialize this constants for Simulink. One more useful way is to create script containing all your variables and load it at Simulink model starts. You can do it by adding script name in Simulink/Model Explorer/Callbacks. (There are different callbacks - on Loading, on Starting and etc.). Read more about this: here.
Now you can run your simulation using sim function:
sim('name_of_model')
name_of_model must contain path if model is not in the active MATLAB folder (active folder you can see in your matlab window just under the main menu).
There are different properties of sim function, read about them in help this can be useful for you. By the way: you can change some parameters of your model using sim. You even can find any block in your model and change it's properties. Read more about sim and about finding current blocks. Interesting that the last solution give you ability to change parameters during the simulation!
About getting output. After you run simulation you get tout variable in main workspace. It is an array of timesteps. But if you add outport block (like at my image) you also get another variable in workspace yout. yout is an Datasets. It contain all your outports values. For 2 outports for example:
yout
yout =
Simulink.SimulationData.Dataset
Package: Simulink.SimulationData
Characteristics:
Name: 'yout'
Total Elements: 2
Elements:
1 : ''
2 : ''
Get the values of any of outports:
yout.get(1).Values
it is a timeseries data type, so:
yout.get(1).Values.Time - give you times
yout.get(2).Values.Data - give you values of this outport at each time
We have one more method to take output values:
[t,x,y] = sim('model_name')
it returns double arrays. t- time array, y - matrix of all outports values (it already double and contain only values without times, but for each simulation time!)
So now you can create common Matlab GUI and work at this variables! There is no any difficulties. You can read more about GUI for Simulink here.
I have one "Thermal Mass" block in Simulink, which represents a thermal mass, which is the ability of a material or combination of materials to store internal energy. In this standard block of Simulink, the initial temperature must be entered. Only one signal can be connected to the block. The source code of the block looks like following:
component mass
% Thermal Mass
% The block represents a thermal mass, which is the ability of a material
% or combination of materials to store internal energy. The property is
% characterized by mass of the material and its specific heat.
%
% The block has one thermal conserving port.
% The block positive direction is from its port towards the block. This
% means that the heat flow is positive if it flows into the block.
% Copyright 2005-2013 The MathWorks, Inc.
nodes
M = foundation.thermal.thermal; % :top
end
parameters
mass = { 1, 'kg' }; % Mass
sp_heat = { 447, 'J/(kg*K)' }; % Specific heat
end
variables
Q = { 0, 'J/s' }; % Heat flow
end
variables(Conversion=absolute)
T = { 300, 'K' }; % Temperature
end
function setup
% Parameter range checking
if mass <= 0
pm_error('simscape:GreaterThanZero','Mass')
end
if sp_heat <= 0
pm_error('simscape:GreaterThanZero','Specific heat')
end
end
branches
Q : M.Q -> *;
end
equations
T == M.T;
Q == mass * sp_heat * T.der;
assert(T>0, 'Temperature must be greater than absolute zero')
end
end
I would like to build another component, whose initial temperature can come from another block, so that it can be also calculated somewhere else. So, one input parameter and everything else should be the same. I am new to Simulink and don't know much about the domains. Any idea, how this can be done?
Thank you!
Parameters entered on a Simulink block are usually utilized for initial values and tuning of block behavior. While newer versions of Simulink will allow you to tune some parameters during simulation, others will be locked down and un-modifiable. This may mean that you need to first execute a model to calculate the initial value for your Thermal Mass, and then start up a second simulation using that temperature as an initial value.
I believe the Simulink help on how to control block parameters will be useful. Depending on the specific design of your model, different techniques found here may be more or less applicable, but generally speaking I know of 2 easy and simple ways to accomplish modifying a mask value.
Set the value to a variable in your Matlab base workspace.
Place the block inside a Masked subsystem. The mask can be used to define a variable that accessible to all the blocks inside it.
This is not possible, while you can execute some pre-processing to determine initial temperature you can not have this as an input from other blocks.
The workaround described by Jared is probably what you're looking for.
It's actually pretty rare to need to do this, if you tell us why you'r looking to set this up, we may be able to help.
I'm trying to model the respective processes of an internal combustion engine. My current modelling approach is to have different sub functions which model the different processes.
Within each sub function is a Level 2 S-Function which solves the ODEs to give the in cylinder state (pressure, temperature, etc).
The problem that I'm having is that each sub function is enabled depending on the current crank angle which is computed from the current timestep in Simulink. The first process works fine as I manually set the initial values, but then I can't pass the latest in-cylinder state (the output from the first sub function) to the second sub function to use as the initial conditions (it insists on using the initial values I set at the beginning of the simulation).
Is there any way round this? Currently I'm going along a path of global data stores, but haven't had any joy so far.
There are a lot of different ways to solve this problem.
I'll show some of them as examples.
You can create additive output with Unit dalay block like this:
So you can get value of your crank angle from previous timestep and USE IT in formula for solving you equations.
Also you can use some code like this:
if (t == 0)
% equations with your initial values
sred = 0;
else
% equations with other values
y = uOld + myCoeef;
end
Another idea: sometimes I use persistent variables in Matlab function to save values of some variable from previous step. But I think it makes calculation slower.
One more idea - if you have Stateflow you can create chart with two states: first for initial moment with your coefficient and second to solve new equations.
If I understood you in wrong way you can show your code and we'll offer some new ideas!
P.S. Example of my using of S-Function:
My S-Function needs 2 values: Q is calculated in simulink at every step, ro is initial I took from big matrix I loaded from workspace in table and took necessary value depending of time.
So there is no any initial values in S-Function - all needed values I transmit into it from simulink!
Question
Is there a way to enforce the simulation step to be smaller than a compile-time constant in a simulink model?
Context
I'm trying to build a PWM block on simulink. As it is now, I have to make sure that the user chooses a step size responsibly (smaller than half the period chosen by him), otherwise the block behaves abnormally. The only way I came up was to stop the simulation if the step size is not small enough, but I find that very annoying (as a user). If possible, I'd like for the user to not worry about this at all.
Here's what I would do: add the following pseudo-code to the block callback StartFcn:
T_PWM = get_param(gcb,...); % get the block parameter (period) of the current PWM block (string)
T_PWM = str2double(T_PWM);
T_solver = get_param(bdroot,'FixedStep'); % get fixed used by the solver (string)
T_solver = str2double(T_solver); % convert from string to double
if T_solver > 0.5*T_PWM
error('Solver step size must be smaller than half the PWM period')
end
I have a MATLAB function block in simulink and for each step simlulink does I want to input a counter with increment 1.
Ex:
1st Step -> Acc=1
2nd Step -> Acc=2
I tried using a Count up block + Pulse generator but the time step of simulink is not constant.
Any ideas?
A common way to do this is to use a sum and a memory block with an initial condition of 0. It should count steps in both fixed and variable step simulations. In fact I believe this would be build and perform very much like an s-function solution during simulation.
Why not just use an integrator block? You can choose with a discreet or continuous integrator block depending on your model type. You can specify the start conditions/value and reset conditions if needed. The image below shows an example of discreet and continuous blocks. Both are just using their default values. To do what you want (adding 1 to the output every step) just define the model sample time as an environment variable (eg sT=0.01) and set the integrator gain to be 1/sT.