*3.1. Cell-based Grid Model*

The simplified cell-based grid model presented here is developed in five steps as shown in Figure 4: (i) cell classification, (ii) cell allocation, (iii) energy aggregation, (iv) development of the grid model and (v) accuracy check. If a grid model containing several voltage levels is to be developed, steps 2 to 4 must be repeated for each voltage level [11].

**Figure 4.** Overview: development of a simplified cell-based model.

In step 1, the original medium-voltage grid is divided into energy cells, considering the grid topology and the topography of the depicted area. As already mentioned in Section 2.1, the cell boundaries of these cells are adapted to the grid units of the traffic analysis. In step 2, the electrical equipment (transformers, lines, grid nodes, busbars, etc.), the consumers and producers are allocated to the individual energy cells. In step 3, the assigned annual energy consumption of the consumers and annual energy production of the producers within an energy cell are aggregated into a fictitious energy node, representing virtual busbars. This aggregation is performed separately for the respective categories of standard load profiles from the BDEW [20] and the synthetic load profiles from the e-control [21]. In step 4, the simplified cell-based grid model is generated by using the software NEPLAN 5.5.6 [19]. For this, a busbar is inserted into the grid model for each energy node. After the implementation of the electrical equipment, it is connected to the energy node. Subsequently, the energy nodes are connected according to the grid topology of the original medium-voltage grid. This connects those cells with each other that enable energy export or import beyond their cell boundaries. Lines within a cell in the original medium-voltage grid structure are taken into account by implementing E-RLC modules in the grid model. In step 5, the accuracy is checked by comparison of the load flows of the simplified cell-based grid model with those of the original medium-voltage grid. We describe this approach of grid simplification in detail in [11].
