Cardinality Dependent Connection Equations

1 CardinalityResistor

In certain cases there is a need to let the behavior of a model be dependent on the number of connections to certain connectors of the model. Below is an example class containing a conditional if-clause equation with a condition that is a parameter expression (the built-in function cardinality has parameter variability), i.e.the condition does not change during simulation. The function cardinality(c) with formal parameter c returns the total number of (internal and external) occurrences of the connector c in connect statements in the total model.

model CardinalityResistor extends Modelica.Electrical.Analog.Interfaces.OnePort; parameter Real R(unit = "Ohm") "Resistance"; equation // Handle cases if pins are not connected if cardinality(p) == 0 and cardinality(n) == 0 then p.v = 0; n.v = 0; elseif cardinality(p) == 0 then p.i = 0; elseif cardinality(n) == 0 then n.i = 0; end if; // Resistor equation v = R * i; end CardinalityResistor;

2 Simulation of CardinalityResistor

model circuit CardinalityResistor R1( R=100 ); Modelica.Electrical.Analog.Basic.Ground Gnd; Modelica.Electrical.Analog.Sources.SineVoltage U1(freqHz = 5, V = 110); equation connect( R1.n, U1.n ); connect( R1.p, Gnd.p ); connect( U1.p, Gnd.p ); end circuit;
loadModel(Modelica);

Simulate it!

simulate( circuit )
plot( R1.v )