OpenModelica
============

`OpenModelica <https://openmodelica.org/>`__ is an open-source
Modelica-based modeling and simulation environment intended for
industrial and academic usage.

Installation of OpenModelica
^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The models shown below were created by using
`OMEdit <https://openmodelica.org/download/download-windows>`__ v1.16.

Using a Linux OS, sometimes may lead to problems while trying to install
OpenModelica. In this case, try to download the pre-built `virtual
machine <https://openmodelica.org/download/virtual-machine>`__.

Mac users are strongly encouraged to run OpenModelica as well as the OMG toolbox in a Linux VM.

Creating Microgrids with OpenModelica
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The microgrids are created with a  user defined library. To start it, run the file *grid.mo* directly in the folder *omg_grid*.


This package contains all components and required for
creating the power electronics driven microgrids, as well as some example networks.

.. figure:: ../../pictures/library1.jpg
   :alt: 

It contains several folders with predefined components,
filters, loads etc. as well as microgrids for the FMU export to Python and some stand-alone examples which can be run directly in OpenModelica.



.. figure:: ../../pictures/omedit.jpg
   :alt: 

Main components of any microgrid are the three-phase inverters. They consist
of three input voltages controlled by a cascaded PI-PI controller in
Python. Default nomenclature for those inputs is i1p1 for
"**i**\ nverter 1 **p**\ hase 1" etc, but it can be changed in the
python code (model\_input=['one', 'two',...] in the env=gym.make()
call).

**Important**: By using filters/loads with inductors or capacitors,
leave the checkbox for the initialization in the provided settings. Changes are likely to
result in errors while creating the FMU or running the Python files.

The provided examples are designed for up to two inverters, but the underlying models can be
easily extended in order to investigate on more complex microgrid topologies.
Extended example showcases are also planed for future releases.

Power Losses
^^^^^^^^^^^^

In the default example "network", no power losses in the inverters or filters are included.
For the latter they can be added by using parts out of the "Filter.LossesFilter" package instead of
the "Filter.IdealFilter" package. Due to a big increase of components and
equations in the ODE-system, the simulation time will increase.
For modeling losses inside the power electronic converters, adding a model in the Python interface
scripts is recommending. Integrating, e.g switching losses, directly in the OpenModelia model will
require to reduce to simulation step size significantly.

For larger simulations with a demand of power loss modeling, it is recommended to
create user defined filters with only the resistors which are needed for
the calculation. To modify them, create a new package (ctrl+N,
specialization: package), duplicate the part which is to modify in the
new package (right-click on it, duplicate, select the previously created
package in path) and modify it there.

Switches / Transistors
^^^^^^^^^^^^^^^^^^^^^^

Modeling switching-like events inside the model,
e.g. triggering loadsteps by adding or removing loads, is
desirable, but difficult to implement with the possibilities of
OpenModelica. Switches in OpenModelica - like in many other free
modelling languages - are designed as resistors. A closed switch has a
low resistance, an open switch a high one. "Removed" loads are still
connected to the grid. Connections with resistors in such dimension
cause numerical issues while simulating as the ODE system becomes stiff.
There are solvers available for stiff equation systems like BDF and
Radau or ones with automatic stiffness detection, but using the switches
often runs into non-converging systems and execution errors.

The working alternative is a parameter-variation of the load. It is
possible to change the parameters of any load during a simulation and
apply loadsteps in this way (see the topic
`Python code <Pythoncode.html>`__).

Setting of v\_DC
^^^^^^^^^^^^^^^^

The DC supply voltage *v*\_DC can be set either directly in the
OpenModelica model or via `Python <Pythoncode.html#setting-of-v-dc>`__.
In the OM model, doubleclick in your network on the inverter, and change
the parameter *v*\_ DC to the demanded value. All three phases of the
inverter will be supplied with the same DC voltage. The default value is
1000 V. The default value can be changed with a right-click on an
inverter, *open class*, select *text view* on the top left corner of the
model canvas, and change the number in the following code line to
the demanded default value:

::

      parameter Real v_DC = 1000;
      

Phase-Locked Loop (PLL)
^^^^^^^^^^^^^^^^^^^^^^^

The PLL blocks are working for simulations in OpenModelica, but out of
structural reasons, the PLL is calculated in Python.