Abstract switch in Modelica

Question

I would like to motivate a question I asked before about a Modelica array of partial model. Consider the following model of a switch between 2 controllers.

model Switch
  input Real u;
  input Integer sel;
  output Real y;
protected 
  Real x;
equation 
  if sel == 1 then
    y = 0.1 * (0 - u);
    der(x) = 0;
  else
    y = 0.1 * (0 - u) + 0.2 * x;
    der(x) = 0 - u;
  end if;
end Switch;

Let's ignore the fact that the PI controller may break when it is not selected for some time due to divergence of x. This can be fixed by resetting x when the PI controller is selected. However, this is not the point here.

I want to abstract this switch in 2 ways. Firstly, to switch among a parametric number of controllers. Secondly, to abstract controllers using partial models. Let Ctrl be the partial model of a controller.

partial model Ctrl
  input Real u;
  output Real y;
end Ctrl;

We can instantiate the two controllers embedded in the switch as follows.

model P extends Ctrl;
equation 
  y = 0.1 * (0 - u);
end P;

model PI extends Ctrl;
protected 
  Real x;
equation 
  y = 0.1 * (0 - u) + 0.2 * x;
  der(x) = 0 - u;
end PI;

The abstract version of the switch is supposed to be something like:

model Switch
  parameter Integer N(min=1);
  Ctrl c[N];
  input Real u;
  input Integer sel(min=1, max=N);
  output Real y;
equation 
  for i in 1:N loop
    c[i].u = u;
  end for;
  y = c[sel].y;
end Switch;

However, this model has some problems. Firstly, it is not clear how this model can be instantiated, e.g. with one P and one PI controller. Secondly, I get a warning which surprises me, namely: The following input lacks a binding equation: c[1].u

Is it possible to do express this abstract switch in Modelica in some way?

Answer 1

This doesn't work with an array of models as you cannot bind it to different models via a modification. You need to specify all the controllers you have inside the GenericSwitch. You could generate the GenericSwitch and Switch model automatically if needed.

partial model Ctrl
  input Real u;
  output Real y;
end Ctrl;

model P 
  extends Ctrl;
equation 
  y = 0.1 * (0 - u);
end P;

model PI 
  extends Ctrl;
protected 
  Real x;
equation 
  y = 0.1 * (0 - u) + 0.2 * x;
  der(x) = 0 - u;
end PI;

model GenericSwitch
  replaceable model MyCtrl1 = Ctrl;
  replaceable model MyCtrl2 = Ctrl;
  MyCtrl1 c1(u = u);
  MyCtrl2 c2(u = u);
  input Real u;
  input Integer sel;
  output Real y;
equation 
  y = if sel == 1 then c1.y else c2.y;
end GenericSwitch;

model Switch = GenericSwitch(
  redeclare model MyCtrl1 = P, 
  redeclare model MyCtrl2 = PI);