Error: Class member redefinition has been found

I have been trying to define a resistor which also produces heat in simscape. The code for the .ssc file is depicted below. When I try to insert the component (via library browser: simscape/utilities/simscape component), I get the error: " Error: Class member redefinition has been found." and "Caused by:

Error using MyPackage.heat_producing_resistor> (line 10)

Class member 'h' is defined.

Error using MyPackage.heat_producing_resistor> (line 16)

Class member 'h' is defined"

What is the problem?

Am i not authorised to define an output?

Is the fault in foundation.electrical.electrical(I don`t understad what that means and if it should be defined differently and why)?

Thanks in advance

component heat_producing_resistor
    %linear resistor
    %Follows the relation U=I*R [V]
    %Includes the heat produced in the resistor dQ/dt =u(t)*i(t) [J/s = W]
    %R is assumed to be constant
    
    nodes
        p = foundation.electrical.electrical; % +:left
        n = foundation.electrical.electrical; % -:right
        dQ = foundation.electical.electrical; % Q:right
    end
    
    variables
        i = {0, 'A' };      %Current (through)
        u = {0, 'V' };      %Voltage (across)
        dQ = {0, 'W' };  %Heatflow (across)
    end
    
    parameters
        R = {1, 'Ohm' };    %resistance
    end
    
    branches
        i : p.i -> n.i;
    end
    
    equations
        assert(R>0)
        v == p.v - n.v;
        v == i*R;
        dQ == i*v;
    end

end

Answer 1

[Pramil]

Hello Maarten,

The error you are getting is expected as “dQ” is a node and not a variable. If you try and assign a value to a node, the complier thinks you are redefining the class and hence the error.

Now, onto the main issue, how to create a resistor which produces heat in Simscape.

As you want to measure heat, use “dQ = foundation.thermal.thermal” instead of “dQ = foundation.electrical.electrical”. The reason for this is if you refer the following documentations:

https://www.mathworks.com/help/simscape/lang/thermal-domain.html

https://www.mathworks.com/help/simscape/lang/electrical-domain.html

You can see that; you can define heat flow “Q” in thermal domain not electrical domain.

To output heat flow through node “dQ”, define a variable “Q” and in “branches” declare that “Q” is of type “dQ.Q” such that it defines heat flow from the component to outside of component.

Finally, equate “Q == i*v” in “equations” for getting the output heat flow. This should create the required block.

Here is the updated code for your reference:

component heat_producing_resistor
    %linear resistor
    %Follows the relation U=I*R [V]
    %Includes the heat produced in the resistor dQ/dt =u(t)*i(t) [J/s = W]
    %R is assumed to be constant
    
    nodes
        p = foundation.electrical.electrical; % +:left
        n = foundation.electrical.electrical; % -:right
        dQ = foundation.thermal.thermal; % Q:right
    end
        
    variables
        i = {0, 'A' };      %Current (through)
        v = {0, 'V' };      %Voltage (across)
        Q = {0, 'J/s'};
    end
    
    parameters
        R = {1, 'Ohm' };    %resistance
    end
    
    branches
        i : p.i -> n.i;
        Q : dQ.Q -> *;
    end
    
    equations
        assert(R>0)
        v == p.v - n.v;
        v == i*R;
        Q == i*v; % Heat flow
    end
end

Hope it helps.