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Reformulated InductiveLoad to avoid infinite value (#3780)
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For #3776
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@mwetter
mwetter authored Apr 6, 2024
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13 changes: 12 additions & 1 deletion Buildings/Electrical/Interfaces/InductiveLoad.mo
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Expand Up @@ -24,7 +24,11 @@ protected
"Magnetic flux";
Modelica.Units.SI.Impedance Z[2] "Impedance of the load";
Modelica.Units.SI.AngularVelocity omega "Angular frequency";
Modelica.Units.SI.Power Q=P*tan(acos(pf_internal))
Modelica.Units.SI.Power Q=P*tan(acos(
Buildings.Utilities.Math.Functions.smoothMin(
x1=pf_internal,
x2=0.99999,
deltaX=0.0000025)))
"Reactive power (positive because inductive load)";
equation
connect(pf_in, pf_internal);
Expand All @@ -36,6 +40,13 @@ equation
annotation (Documentation(revisions="<html>
<ul>
<li>
April 4, 2024, by Michael Wetter:<br/>
Reformulated calculation of reactive power to bound argument of tangent away from &pi;,
which avoids an infinite function value.<br/>
This is for
<a href=\"https://github.com/lbl-srg/modelica-buildings/issues/3776\">Buildings, #3776</a>.
</li>
<li>
June 06, 2014, by Marco Bonvini:<br/>
Added power factor input <code>pf_in</code> and updated documentation.
</li>
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42 changes: 21 additions & 21 deletions ...ings/Resources/Documentation/userGuide/build/html/_sources/bestPractice.rst.txt
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Expand Up @@ -42,9 +42,9 @@ Building large system models
When creating a large system model, it is typically easier to build the system model
through the composition of subsystem models that can be tested in isolation. For example,
the package
`Buildings.Examples.ChillerPlant.BaseClasses.Controls.Examples <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Examples_ChillerPlant_BaseClasses_Controls_Examples.html#Buildings.Examples.ChillerPlant.BaseClasses.Controls.Examples>`_
`Buildings.Examples.ChillerPlant.BaseClasses.Controls.Examples <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Examples_ChillerPlant_BaseClasses_Controls_Examples.html#Buildings.Examples.ChillerPlant.BaseClasses.Controls.Examples>`_
contains small test models that are used to test individual components in the large system model
`Buildings.Examples.ChillerPlant <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Examples_ChillerPlant.html#Buildings.Examples.ChillerPlant>`_.
`Buildings.Examples.ChillerPlant <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Examples_ChillerPlant.html#Buildings.Examples.ChillerPlant>`_.
Creating small test models typically saves time as the proper response of controls, and the proper operation of subsystems, can be tested in isolation of complex system-interactions that are often present in large models.


Expand Down Expand Up @@ -270,9 +270,9 @@ a fluid port represents the physical phenomena that was intended to model.

However, in more complex flow configurations, one may want to explicitly control what branches of a piping or duct network mix.
This may be achieved by using an instance of the model
`Junction <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_FixedResistances.html#Buildings.Fluid.FixedResistances.Junction>`_
`Junction <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_FixedResistances.html#Buildings.Fluid.FixedResistances.Junction>`_
as shown in the left figure below, which is derived from the test model
`BoilerPolynomialClosedLoop <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Boilers_Examples.html#Buildings.Fluid.Boilers.Examples.BoilerPolynomialClosedLoop>`_
`BoilerPolynomialClosedLoop <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Boilers_Examples.html#Buildings.Fluid.Boilers.Examples.BoilerPolynomialClosedLoop>`_

.. _fig_flu_cor_wro:

Expand All @@ -283,7 +283,7 @@ as shown in the left figure below, which is derived from the test model

In :numref:`fig_flu_cor_wro` (a), the mixing points have been correctly defined by
use of the model
`Junction <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_FixedResistances.html#Buildings.Fluid.FixedResistances.Junction>`_.
`Junction <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_FixedResistances.html#Buildings.Fluid.FixedResistances.Junction>`_.
However, in :numref:`fig_flu_cor_wro` (b), all connections are made to the port of the instance ``spl2``.
This results in the same configuration as is shown in :numref:`fig_flu_cor_wro` (c).
This is certainly not the intention of the modeler, as this causes all flows to be mixed in the port.
Expand All @@ -301,13 +301,13 @@ Use of sensors in fluid flow systems
When selecting a sensor model, a distinction needs to be made whether the measured quantity depends on
the direction of the flow or not. If the quantity depends on the flow direction,
such as temperature or relative humidity, then sensors with two ports from the
`Buildings.Fluid.Sensors <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Sensors.html#Buildings.Fluid.Sensors>`_
`Buildings.Fluid.Sensors <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Sensors.html#Buildings.Fluid.Sensors>`_
library should be used. These sensors have a more efficient implementation than sensors with
one port for situations where the flow reverses its direction.
The proper use sensors is described in the
`User's Guide <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Sensors_UsersGuide.html>`_
`User's Guide <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Sensors_UsersGuide.html>`_
of the
`Buildings.Fluid.Sensors <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Sensors.html#Buildings.Fluid.Sensors>`_
`Buildings.Fluid.Sensors <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Sensors.html#Buildings.Fluid.Sensors>`_
package.


Expand All @@ -319,9 +319,9 @@ Reference pressure for incompressible fluids such as water
This section explains how to set a reference pressure for fluids that model
the flow as :term:`incompressible flow`,
such as
`Buildings.Media.Water <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Media_Water.html#Buildings.Media.Water>`_
`Buildings.Media.Water <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Media_Water.html#Buildings.Media.Water>`_
and
`Buildings.Media.Antifreeze.PropyleneGlycolWater <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Media_Antifreeze_PropyleneGlycolWater.html#Buildings.Media.Antifreeze.PropyleneGlycolWater>`_.
`Buildings.Media.Antifreeze.PropyleneGlycolWater <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Media_Antifreeze_PropyleneGlycolWater.html#Buildings.Media.Antifreeze.PropyleneGlycolWater>`_.

Consider the flow circuit shown in :numref:`fig_flow_cir` that consists of a pump or fan,
a flow resistance and a volume.
Expand Down Expand Up @@ -354,7 +354,7 @@ In this situation, attempting to translate the model leads, in Dymola, to the fo
The number of scalar Real equation elements are 58.
Similarly, if the medium model
`Buildings.Media.Specialized.Water.TemperatureDependentDensity <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Media_Specialized_Water_TemperatureDependentDensity.html#Buildings.Media.Specialized.Water.TemperatureDependentDensity>`_,
`Buildings.Media.Specialized.Water.TemperatureDependentDensity <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Media_Specialized_Water_TemperatureDependentDensity.html#Buildings.Media.Specialized.Water.TemperatureDependentDensity>`_,
which models density as a function of pressure and enthalpy, is used, then
the model is well-defined, but the pressure increases the longer the pump runs.
The reason is that the pump adds heat to the water. When the water temperature
Expand All @@ -364,7 +364,7 @@ the pressure increases from :math:`1 \, \mathrm{bars}` to :math:`150 \, \mathrm{
To avoid this singularity or increase in pressure,
use a model that imposes a pressure source and that accounts for the expansion of the fluid.
For example, use
`Buildings.Fluid.Sources.Boundary_pT <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Sources.html#Buildings.Fluid.Sources.Boundary_pT>`_
`Buildings.Fluid.Sources.Boundary_pT <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Sources.html#Buildings.Fluid.Sources.Boundary_pT>`_
to form the system model shown in :numref:`fig_flow_cir_wit_bou`.

.. _fig_flow_cir_wit_bou:
Expand All @@ -376,15 +376,15 @@ to form the system model shown in :numref:`fig_flow_cir_wit_bou`.
provides a reference presssure.

Alternatively, you may use
`Buildings.Fluid.Storage.ExpansionVessel <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Storage.html#Buildings.Fluid.Storage.ExpansionVessel>`_,
`Buildings.Fluid.Storage.ExpansionVessel <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Storage.html#Buildings.Fluid.Storage.ExpansionVessel>`_,
but
`Buildings.Fluid.Sources.Boundary_pT <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Sources.html#Buildings.Fluid.Sources.Boundary_pT>`_
`Buildings.Fluid.Sources.Boundary_pT <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Sources.html#Buildings.Fluid.Sources.Boundary_pT>`_
usually leads to simpler equations than
`Buildings.Fluid.Storage.ExpansionVessel <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Storage.html#Buildings.Fluid.Storage.ExpansionVessel>`_.
`Buildings.Fluid.Storage.ExpansionVessel <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Storage.html#Buildings.Fluid.Storage.ExpansionVessel>`_.
Note that the medium that flows out of the fluid port of
`Buildings.Fluid.Sources.Boundary_pT <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Sources.html#Buildings.Fluid.Sources.Boundary_pT>`_
`Buildings.Fluid.Sources.Boundary_pT <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Sources.html#Buildings.Fluid.Sources.Boundary_pT>`_
is at a fixed temperature, while the model
`Buildings.Fluid.Storage.ExpansionVessel <https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Storage.html#Buildings.Fluid.Storage.ExpansionVessel>`_
`Buildings.Fluid.Storage.ExpansionVessel <https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Storage.html#Buildings.Fluid.Storage.ExpansionVessel>`_
conserves energy.
However, since the thermal expansion of the fluid is usually small,
this effect can be neglected in most building HVAC applications.
Expand All @@ -393,10 +393,10 @@ this effect can be neglected in most building HVAC applications.

In each water circuit, there must be exactly on instance of
`Buildings.Fluid.Sources.Boundary_pT
<https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Sources.html#Buildings.Fluid.Sources.Boundary_pT>`_,
<https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Sources.html#Buildings.Fluid.Sources.Boundary_pT>`_,
or instance of
`Buildings.Fluid.Storage.ExpansionVessel
<https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_Storage.html#Buildings.Fluid.Storage.ExpansionVessel>`_.
<https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_Storage.html#Buildings.Fluid.Storage.ExpansionVessel>`_.

If there is more than one such device, then there are multiple
points in the system that set the reference static pressure.
Expand Down Expand Up @@ -592,5 +592,5 @@ is produced. This shows the iteration variables and their start values.
These start values can be overwritten in the model.


.. _PressureDrop: https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_FixedResistances.html#Buildings.Fluid.FixedResistances.PressureDrop
.. _WetCoilDiscretized: https://simulationresearch.lbl.gov/modelica/releases/v9.1.1/help/Buildings_Fluid_HeatExchangers.html#Buildings.Fluid.HeatExchangers.WetCoilDiscretized
.. _PressureDrop: https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_FixedResistances.html#Buildings.Fluid.FixedResistances.PressureDrop
.. _WetCoilDiscretized: https://simulationresearch.lbl.gov/modelica/releases/v10.0.0/help/Buildings_Fluid_HeatExchangers.html#Buildings.Fluid.HeatExchangers.WetCoilDiscretized
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