How to create a custom capacitor with changing distance between capacitor plates?

Hello.

How to create a custom capacitor with changing distance between capacitor plates?

Excuse for troubling.

component capacitor

   nodes
        p = foundation.electrical.electrical; % +:top
        n = foundation.electrical.electrical; % -:bottom
   end
    
  inputs
      d2 = { 0.01, 'mm' }; % :bottom
  end

  parameters
        d1 = { 0.01, 'mm' };
        C0 = { 1, 'F' };    % Nominal capacitance C0 at V=0
        Cv = { 0.2, 'F/V'}; % Rate of change of C with voltage V
        R = {2, 'Ohm' };    % Effective series resistance
        Rd = {500, 'Ohm' }; % Self-discharge resistance
        
    end

    variables
        i = { 0, 'A'   }; % Current
        vc = {value = { 0, 'V' }, priority = priority.high}; % Capacitor voltage
    end

    branches
        i : p.i -> n.i; % Through variable i from node p to node n
    end

    equations
        assert(C0 > 0)
        assert(R > 0)
        assert(Rd > 0)
        let
            v = p.v-n.v; % Across variable v from p to n
        in
            v == vc; 
            i == (C0*k)*der(vc*(d2/d1));
%             k =    e*e0*S/d2
        end
    end

end

[Alexander Vasilev]

            v == vc*(d2/d1); 
            i == C0*der(v);
%             k =    e*e0*S/d2

Don't work too.

Voltage does not increase.

For simplicity, I have not changed the capacity yet.

Answer 1

[David John]

If you want to change the capacitance based on an input, you can have something like

i == C0*d1/d2*vc.der;

I'm not sure what you mean when you say that "the voltage does not increase". If you can share your test model, I can probably comment on that as well.

[David John]

By the way, if you have Simscape Electrical, then there is a "Variable Capacitor" block that does something similar to what you want.