modelLoad

Partial model for a generic load
Diagram of LoadOpen the diagram
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Information

This model represents a generic load that can be extended to represent either a DC or an AC load.

The model has a single generalized electric terminal of type Buildings.Electrical.Interfaces.Terminal that can be redeclared. The generalized load is modeled as an impedance whose value can change. The value of the impedance can change depending on the value of the parameter mode, which is of type Buildings.Electrical.Types.Load:

Mode Description Explanation
Buildings.Electrical.Types.Load.FixedZ_steady_state fixed Z steady state The load consumes exactly the power specified by the parameter P_nominal.
Buildings.Electrical.Types.Load.FixedZ_dynamic fixed Z dynamic The load consumes exactly the power specified by the parameter P_nominal at steady state. Depending on the type of load (e.g., inductive or capacitive) different dynamics are represented.
Buildings.Electrical.Types.Load.VariableZ_P_input variable Z P input The load consumes exactly the power specified by the input variable Pow.
Buildings.Electrical.Types.Load.VariableZ_y_input variable Z y input The load consumes exactly the a fraction of the nominal power P_nominal specified by the input variable y.

Conventions

It is assumed that the power P of the load is positive when produced (e.g., the load acts like a source) and negative when consumed (e.g., the source acts like a utilizer).

Linearized models

The model has a Boolean parameter linearized that by default is equal to false. When the power consumption of the load is imposed, this introduces a nonlinear equation between the voltage and the current of the load. This flag is used to select between a linearized version of the equations or the original nonlinear ones.
When the linearized version of the model is used, the parameter V_nominal has to be specified. The nominal voltage is needed to linearize the nonlinear equations.

Note: A linearized model will not consume the nominal power if the voltage at the terminal differs from the nominal voltage.

Parameters

TypeNameDefaultDescription
Modeling assumption
BooleanlinearizedfalseIf true, the load model is linearized
Buildings.Electrical.Types.LoadmodeBuildings.Electrical.Types.Load.FixedZ_steady_stateType of load model (e.g., steady state, dynamic, prescribed power consumption, etc.)
Nominal conditions
Modelica.Units.SI.PowerP_nominal0Nominal power (negative if consumed, positive if generated). Used if mode <> Buildings.Electrical.Types.Load.VariableZ_P_input
Modelica.Units.SI.VoltageV_nominalNominal voltage (V_nominal >= 0)
Initialization
Buildings.Electrical.Types.InitModeinitModeBuildings.Electrical.Types.InitMode.linearizedInitialization mode for homotopy operator

Connectors

TypeNameDefaultDescription
Modelica.Blocks.Interfaces.RealInputyFraction of the nominal power consumed
Modelica.Blocks.Interfaces.RealInputPowPower consumed
Buildings.Electrical.Interfaces.TerminalterminalGeneralized electric terminal

Components

TypeNameDefaultDescription
Modelica.Units.SI.Voltage[:]vterminal.vVoltage vector
Modelica.Units.SI.Current[:]iterminal.iCurrent vector
Modelica.Units.SI.Power[PhaseSystem.n]SPhaseSystem.phasePowers_vi(v, -i)Phase powers
Modelica.Units.SI.PowerPPower of the load (negative if consumed, positive if fed into the electrical grid)

Contents

NameDescription
PhaseSystem

Revisions

  • November 14, 2024, by Michael Wetter:
    Changed default initialization method to using linearized model rather than zero current, as the latter causes a division by zero in OpenModelica during the homotopy initialization.
    This is for Buildings, #4048.
  • January 30, 2019, by Michael Wetter:
    Set start value for P.
  • November 28, 2016, by Michael Wetter:
    Removed zero start value for current. The current is typically non-zero and zero is anyway the default start value, hence there is no need to set it.
    This is for #584.
  • September 17, 2016, by Michael Wetter:
    Corrected wrong annotation to avoid an error in the pedantic model check in Dymola 2017 FD01 beta2.
    This is for issue 557.
  • February 26, 2016, by Michael Wetter:
    Set default value for P_nominal and removed assertion warning. This is required for pedantic model check in Dymola. This is for #426.
  • September 24, 2015 by Michael Wetter:
    Provided value for P_nominal if mode <> Buildings.Electrical.Types.Load.VariableZ_P_input. This avoids a warning during translation of Buildings.Examples.ChillerPlant.DataCenterRenewables.
  • September 4, 2014, by Michael Wetter:
    Changed the parameter from linear to linearized because Buildings.Fluid also uses linearized. This change has been done to use a consistent naming across the library.
  • June 17, 2014, by Marco Bonvini:
    Adde parameter initMode that can be used to select the assumption to be used during initialization phase by the homotopy operator.
  • May 15, 2014, by Marco Bonvini:
    Created documentation and revised model.
  • October 31, 2013, by Marco Bonvini:
    Model included in the Buildings library.