## 3 Results and Discussion
### Analysis of the Relationship between the Grid Voltage and the Power Generated by the Inverters  
To further analyse the influence of PV plant production on the increase in grid voltage values, the correlation between the value of the grid voltage and the power generated in each PV installation was studied in detail. For this purpose, the value of the grid voltage \(V_{AC}\) was represented on the \(Y\)-axis, and the value of the power injected into the grid at each time instant \(P_{AC}\) was represented on the X-axis. Both parameters were measured by the inverters. Due to the large volume of data to be processed, these graphs were made for each of the months corresponding to the period monitored, and in each of the three different phases. Given the particularities of each installation, the following shows how this analysis was carried out in each one of them. Plant 1. This installation consists of three three-phase inverters in which the power generated by each inverter is injected into the grid, distributing production evenly among the three phases. The inverters provide the voltage in each of the phases. Therefore, the \(V_{AC}\) voltage value of each phase was represented with respect to \(P_{AC}\) value resulted from the  
Figure 14: Values of the grid voltage measured by the inverters in one of the phases in each of the PV installations analysed, when there is production from the installation being fed into the grid. Plant 2. This installation has two three-phase inverters, of the same model as those in plant 1, in which the power generated in each inverter is divided by three to be injected in a balanced way in each of the phases. In this case, the \(V_{AC}\) voltage value of each phase was represented with respect to the sum of the \(P_{AC}\) power produced by the two inverters and in turn divided by three due to the distribution between the three phases. Plant 3. This installation has six single-phase inverters distributed in such a way that they inject into each of the phases in groups of two. As they are single-phase inverters, each inverter only measures the voltage value corresponding to the phase to which it is connected. In this case, the \(V_{AC}\) voltage of each phase recorded by one of the inverters connected to each phase was plotted against the sum of the \(P_{AC}\) power generated by the two inverters connected to the same phase. Plant 4. In the case of this installation, there are three single-phase inverters, each of which is connected to a different phase. The \(V_{AC}\) voltage measured by each inverter on the phase into which it injects was therefore plotted against the \(P_{AC}\) power generated by the same inverter. Plant 5. In this case, this installation has 18 single-phase inverters that inject into each of the phases in groups of six inverters. The \(V_{AC}\) measured by one of the inverters injecting on each phase was plotted against the sum of the \(P_{AC}\) power generated by the six inverters injecting together on the same phase. Plant 6. As in the case of plant 4, there are three single-phase inverters, each of which is connected to a different phase. The \(V_{AC}\) voltage measured by each inverter was therefore plotted against the \(P_{AC}\) power generated by the same inverter. In these graphical representations of \(V_{AC}\) versus \(P_{AC}\), the voltage limits established in the current standard were also included. The standard EN-50160 \"Voltage characteristics of electricity supplied by public electricity networks\", indicates that the supply voltage variations must be 95% of time within the range 230 \(\pm\) 10% at all supply terminals of the LV network [44]. Therefore, the lower and upper permissible levels for this parameter of the grid signal, corresponding respectively to the values 207-253 V, were represented in the figures in red. In each of these graphical representations, the point cloud was fitted with a linear regression line, and this line was shown in green.