Expressing Event Behavior in Modelica

1 Expressing Event Behavior in Modelica

The conditional equations associated with an event become active when the condition of the equations switches from the value false and true. There are basically two groups of conditional equation constructs in Modelica: if-equations and when-equations. In the Diode example below different equations are specified.

1.1 Electrical Units

type Voltage = Real(unit = "V");
type Current = Real(unit = "A");

1.2 Electrical Connectors

connector Pin "Pin of an electrical component" Voltage v "Potential at the pin"; flow Current i "Current flowing into the pin"; end Pin; //From Modelica.Electrical.Analog.Interfaces
connector PositivePin "Positive pin of an electrical component" Voltage v "Potential at the pin"; flow Current i "Current flowing into the pin"; end PositivePin; //From Modelica.Electrical.Analog.Interfaces
connector NegativePin "Negative pin of an electrical component" Voltage v "Potential at the pin"; flow Current i "Current flowing into the pin"; end NegativePin; //From Modelica.Electrical.Analog.Interfaces

1.3 Electrical Components

partial model TwoPin // Same as OnePort in Modelica.Electrical.Analog.Interfaces "Component with two electrical pins p and n and current i from p to n" Voltage v "Voltage drop between the two pins (= p.v - n.v)"; Current i "Current flowing from pin p to pin n"; PositivePin p; NegativePin n; equation v = p.v - n.v; 0 = p.i + n.i; i = p.i; end TwoPin;

1.4 Diode

The if-equation in the ideal diode example below, specifies different equations for the variable v in two different operating regions: the v = s in the region s and the equation v = 0 in the region s >= 0.

model Diode "Ideal diode" extends TwoPin; Real s; Boolean off; equation off = s < 0; if off then // conditional if-equation v = s; else v = 0; end if; i = if off then 0 else s; // equation with conditional expression end Diode;