Simulink Model for ohmic heating in a resistor

I need to model temperature rise of a resistor due to joule heating with a variable supply or a variable resistor. Is there a simulink component that can be used for this or it has to be implemented with the physical equations fed into block diagrams?

Can someone help give an idea of how this can be modeled?

Answer 1

[David John]

Have a look at the Variable Resistor and Thermal Resistor blocks. The source code should be available for both of these blocks.

If you start from the Thermal Resistor source code, you can simply change R from being a parameter to being an input:

inputs

R = { 0.0, 'Ohm' }; % R:left

end

[Mukti Chaturvedi]

Thanks @David John for helpful response. Changing R to input is for making it a variable resistor? And how will the component be saved? not able to save the modified file for the access denial.

[David John]

If you just need to model the temperature rise influencing the resistance, the Thermal Resistor block probably already does what you want. See Resistor with thermal port - MATLAB (mathworks.com) for details.

In your original post, you mentioned making the resistance variable as well, and I interpreted this to mean that you wanted to vary the base resistance (i.e., the resistance at the nominal temperature) as well. You can define the resistance as an input in this case in order to have it control the value of this base resistance while the simulation is running (e.g., if your simulation involves something like a temperature-dependent potentiometer or something that is changing value during the simulation).

In terms of saving the file, you can save it to your own directory somewhere that is on the MATLAB path. Check out Generating Custom Blocks from Simscape Component Files - MATLAB & Simulink (mathworks.com) for some tips on how to use your new custom block in your model.

[Mukti Chaturvedi]

Thanks a lot for detailed description. Yes, i wanted the resistance to be variable for the analysis. I will try again making it as an input.

Also, I need to take temperature readings from the temperature sensor, with respect to variation in current. Currently, the reading shown does not seem to be of the corresponding temperature. Can you suggest how can variation of temperature due to joule heating can be observed with variation of current.

[David John]

You need a Thermal Resistance between the A port on the Temperature Sensor and the Thermal Reference. Without this, the power dissipated by the resistor is going all into the thermal mass of the resistor itself. This would be like connecting a current source directly to a capacitor in the electrical domain: the voltage would just ramp up continually. In the thermal domain, heat flow behaves like current, and temperature behaves like voltage. You also do not need a powergui block in this model since you are not using any components from the Specialized Power Systems library.

[Mukti Chaturvedi]

added a thermal resistor to the block, but not observing any change. Can you kindly help more on this.

Also, can you suggest a forum where small details like these can be talked and know about, apart form questions here. There are other models that i am working upon for which I need help. Thanks a lot.

[David John]

Please see the model that I attached to my previous response. In your model, you have placed the thermal resistance in series with a temperature sensor. No heat can flow through a temperature sensor, so your thermal resistor is not doing anything. It should be in parallel to the sensor...from A on the senor to the thermal reference rather than from B.

If you have a current license, you can also reach out to our technical support organization for help. We also offer more intensive support and consulting when appropriate.

[Mukti Chaturvedi]

Thanks for the helpful explanation.

[Mukti Chaturvedi]

Further, i also need to understand how to incorporate these

(i) find the variation in resistance with respect to temperature

(ii) plot the temperature rise of the resistor with respect to current variation

[David John]

Log and Plot Simulation Data - MATLAB & Simulink (mathworks.com)

[Mukti Chaturvedi]

Thanks. I will check the given link, but the resistance and temeperature variation is not observed in the model, currently.

resistance variation with time and resistance variation with temperature - how can that be observed.

Temperature variation with time can it be observed with this model?

[David John]

If you are making a custom block, change the line "intermediates (Access=private, ExternalAccess=none)" to "intermediates (Access=private, ExternalAccess=observe)", and then R will appear in the simlog.

Or simply extract i, p.v and n.v from the simlog and plot (p.v-n.v)./i against T.

[Mukti Chaturvedi]

Thanks you for all the help. I have tried getting a plot wrt time and also resistance wrt Temperature. Attached the model with the plot options. Supply voltage is now given as 70V.

Now, please suggest how can a temperature check be included in a way so that when temperature exceeds 1000 degree C, then supply voltage has to be changed to 100 V for 0.02s.

I am not aware of MATLAB coding, but stil,can a source code of this model be generated?