The Modelica standard library defines the most important elementary connectors in various domains. If any possible, a user should utilize these connectors in order that components from the Modelica Standard Library and from other libraries can be combined without problems. The following elementary connectors are defined (the meaning of potential, flow, and stream variables is explained in section "Connector Equations" below):
domain | potential variables |
flow variables |
stream variables |
connector definition | icons |
electrical analog |
electrical potential | electrical current | Modelica.Electrical.Analog.Interfaces Pin, PositivePin, NegativePin |
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electrical multi-phase |
vector of electrical pins | Modelica.Electrical.MultiPhase.Interfaces Plug, PositivePlug, NegativePlug |
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electrical space phasor |
2 electrical potentials | 2 electrical currents | Modelica.Electrical.Machines.Interfaces SpacePhasor |
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quasi stationary single phase |
complex electrical potential | complex electrical current |
Modelica.Electrical.QuasiStationary.SinglePhase.Interfaces Pin, PositivePin, NegativePin |
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quasi stationary multi-phase |
vector of quasi stationary single phase pins |
Modelica.Electrical.QuasiStationary.MultiPhase.Interfaces Plug, PositivePlug, NegativePlug |
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electrical digital |
Integer (1..9) | Modelica.Electrical.Digital.Interfaces DigitalSignal, DigitalInput, DigitalOutput |
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magnetic flux tubes |
magnetic potential | magnetic flux | Modelica.Magnetic.FluxTubes.Interfaces MagneticPort, PositiveMagneticPort, NegativeMagneticPort |
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magnetic fundamental wave |
complex magnetic potential | complex magnetic flux | Modelica.Magnetic.FundamentalWave.Interfaces MagneticPort, PositiveMagneticPort, NegativeMagneticPort |
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translational | distance | cut-force | Modelica.Mechanics.Translational.Interfaces Flange_a, Flange_b |
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rotational | angle | cut-torque | Modelica.Mechanics.Rotational.Interfaces Flange_a, Flange_b |
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3-dim. mechanics |
position vector orientation object |
cut-force vector cut-torque vector |
Modelica.Mechanics.MultiBody.Interfaces Frame, Frame_a, Frame_b, Frame_resolve |
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simple fluid flow |
pressure specific enthalpy |
mass flow rate enthalpy flow rate |
Modelica.Thermal.FluidHeatFlow.Interfaces FlowPort, FlowPort_a, FlowPort_b |
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thermo fluid flow |
pressure | mass flow rate | specific enthalpy mass fractions |
Modelica.Fluid.Interfaces FluidPort, FluidPort_a, FluidPort_b |
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heat transfer |
temperature | heat flow rate | Modelica.Thermal.HeatTransfer.Interfaces HeatPort, HeatPort_a, HeatPort_b |
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blocks | Real variable Integer variable Boolean variable |
Modelica.Blocks.Interfaces RealSignal, RealInput, RealOutput IntegerSignal, IntegerInput, IntegerOutput BooleanSignal, BooleanInput, BooleanOutput |
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complex blocks |
Complex variable | Modelica.ComplexBlocks.Interfaces ComplexSignal, ComplexInput, ComplexOutput |
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state machine |
Boolean variables (occupied, set, available, reset) |
Modelica.StateGraph.Interfaces Step_in, Step_out, Transition_in, Transition_out |
In all domains, usually 2 connectors are defined. The variable declarations are identical, only the icons are different in order that it is easy to distinguish connectors of the same domain that are attached at the same component.
Modelica supports also hierarchical connectors, in a similar way as hierarchical models. As a result, it is, e.g., possible, to collect elementary connectors together. For example, an electrical plug consisting of two electrical pins can be defined as:
connector Plug import Modelica.Electrical.Analog.Interfaces; Interfaces.PositivePin phase; Interfaces.NegativePin ground; end Plug;
With one connect(..) equation, either two plugs can be connected (and therefore implicitly also the phase and ground pins) or a Pin connector can be directly connected to the phase or ground of a Plug connector, such as "connect(resistor.p, plug.phase)".
The connector variables listed above have been basically determined with the following strategy:
The Modelica connection semantics is sketched at hand of an example: Three connectors c1, c2, c3 with the definition
connector Demo Real p; // potential variable flow Real f; // flow variable stream Real s; // stream variable end Demo;
are connected together with
connect(c1,c2); connect(c1,c3);
then this leads to the following equations:
// Potential variables are identical c1.p = c2.p; c1.p = c3.p; // The sum of the flow variables is zero 0 = c1.f + c2.f + c3.f; /* The sum of the product of flow variables and upstream stream variables is zero (this implicit set of equations is explicitly solved when generating code; the "<undefined>" parts are defined in such a way that inStream(..) is continuous). */ 0 = c1.f*(if c1.f > 0 then s_mix else c1.s) + c2.f*(if c2.f > 0 then s_mix else c2.s) + c3.f*(if c3.f > 0 then s_mix else c3.s); inStream(c1.s) = if c1.f > 0 then s_mix else <undefined>; inStream(c2.s) = if c2.f > 0 then s_mix else <undefined>; inStream(c3.s) = if c3.f > 0 then s_mix else <undefined>;