Internal Process of Structural Optimization
Although the simulation with structural optimization components can be executed in exactly the same way as a conventional simulation, there are some special features in the internal simulation process. It is not necessary for the user to understand them in detail, but knowledge of them can be useful.
The usual simulation process (reading the model, determining the simulation time steps, etc.) is extended by several steps for structural optimization:
Time Series Compression
In structural optimization, a plant size is optimized over the entire simulation period and not just for individual points in time. The optimization problem is time coupled. Select the Compression level for the automatic time series compression. Depending on this selection, there are two different processes of structural optimization: Structural optimization with time series compression takes place in the so-called simplified pre-stage, and operational optimization subsequently follows in the main stage.
With the time series compression level No compression/exactly, no time series compression takes place, and the structural optimization is not executed in an extra step, but together with the operational optimization in the so-called Main stage without the need for a preliminary stage. This also applies to the combination of structural optimization and optimization with year-round coupled constraints without time series compression. Without time series compression, the intermediate steps “storage of structural variables in the simulation node” and “selection of a solution” are also omitted. In this case, the objective function of the Operational optimization in the Simulation ribbon is grayed out, and it is effectively an operational optimization with integrated structural variables.
If both structural optimization and optimization with year-round coupled constraints are activated in the simulation node, the algorithm for Optimization with year-round coupled constraints replaces the time series compression algorithm.
MILP for Structural Optimization
In structural optimization, a coupled optimization problem is calculated on the basis of the previously compressed time series. The computing time depends strongly on the solver used, the problem size, and the selected compression level. The Results of the structural variables (dimensioning, investment costs, purchase decision) are stored in the Simulation node and displayed under Structural optimization in the Simulation form after optimization.
Operational Optimization
After an optimal structure has been calculated, it is fixed. Based on this structure, an operational optimization is then carried out. This operational optimization is not different from conventional operational optimization. Operation can be optimized on the basis of the original uncompressed time series because this is based on a fixed structure. All Operational side conditions can also be used in the model, but some operating constraints are not considered in the structural optimization (see the linked article). Therefore, if optimization cannot be performed for certain time steps under certain circumstances, the following error message appears.
Another possible cause of errors are additive demands that are parameterized in various components. This problem can be solved by summarizing the demands in one component (see above).
For more information on troubleshooting, see the linked article Error Messages.
