How can I create a variable resistor for use in SimPowerSystems?
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MathWorks Support Team on 15 Nov 2021
Edited: MathWorks Support Team on 16 Nov 2021
Simscape, released in R2007a, contains a block called "Variable Resistor":
If you do not have access to Simscape, the attached model shows an example on how to achieve this. This model should also work in most previous versions. Note that the model contains an algebraic loop, but Simulink is able to resolve it and the simulation runs fine with correct results.
In this example model "ControlledResistor_mod_7b.slx", we are directly modifying the current going through the resistor. In a physical sense, this is exactly what a variable resistor does. It limits the amount of electrons going through it by limiting the current. A singularity at R = 0 should never happen because 0 is not a physical resistor value. It should be variable between A and B wherein A,B > 0.
For modelling in SimPowerSystems, one should think in physical terms rather than in mathematical terms. In this model, the approach of computing the voltage that you want the resistor to hold and forcing the appropriate current (I = U/R) through it with a source is taken since it is the practical method in physical terms as opposed to computing the current and forcing the corresponding voltage.
"ControlledResistor_mod_7b.slx" can be modified to "VoltageControlledResistor.slx" for cases when one needs to model a voltage-controlled variable resistor. You can modify the voltage measured across a resistor ("R_var" in the example) as desired in the function block so the resistance is a function of voltage.
More Answers (9)
Sriram Narayanan on 13 Jan 2015
Please right-click the attachment and select "Save Link As" and then you should be able to save the attachment and open the model in Simulink.
NageswaraRao kudithi on 25 Jul 2017
hey please can you attach the file to this email:firstname.lastname@example.org
Alasdair Robertson on 8 Nov 2017
I am looking into Variable Resistor models for my Masters Project I am currently carrying out. I came across this model and, though it seems helpful, I am having a bit of trouble understanding certain aspects of it.
My main issue is with the Multimeter object. I'm not entirely sure what this object is doing and how it operates. I understand its giving out a constant 100v signal from the first output, but I don't understand why the other outputs are following a trend set by the "step generator" which I'm assuming is closely representing the operation of our Variable Resistance, and then why we are subtracting this value from the initial 100v output before passing it into the dividing block.
I can see that this model is behaving as a Variable Resistor, controlling the current throughout the circuit, I'm just unsure how the Multimeter is hooked up to the step generator, and what the outputs on the multimeter are relating to.
Any help is much appreciated!
Thanks guys, Ali.