## 4 Results of Measurements
This resistance limits the maximum value of the charging current, and its increase results in an extension of the charging time [27]. This limitation translates into a limitation of the input current amplitude of the charging system and a reduction in the distortion of this current. Figures 11-13 show the influence of the load resistance \(\mathrm{R_{o}}\) on the operating parameters of the charging system. The values of individual operating parameters were measured for the RMS value of the power grid voltage \(\mathrm{V_{inRMS}}=230\) V and for three selected values of output voltages \(\mathrm{V_{out}}\) equal to 5, 9, and 20 V, respectively. Changing the output voltage \(\mathrm{V_{out}}\) would not be possible without the use of an external USB PD 3.1 port triggering system. In [41], the full technical and operational documentation of the COM-ZY12 PDN Trigger the USB PD 3.0 system was presented, which allows the dedicated charging system to operate without a connected mobile device and allows output voltage \(\mathrm{V_{out}}\) to be changed within a set range not exceeding 20 V for the tested system. This system acted as a system negotiating the level of the output voltage normally used in mobile devices. Figure 11: Measured dependences of the RMS value of the input current (**a**) and the output current (**b**) on load resistance. Figure 12: Calculated dependence of the total harmonic distortion factor of the current \(\mathrm{THD_{l}}\), the total harmonic distortion factor of the voltage \(\mathrm{THD_{v}}\) (**a**) and the power factor PF (**b**) on load resistance \(\mathrm{R_{o}}\). Figure 11 shows the influence of load resistance \(\mathrm{R_{o}}\) on the RMS value of the input current \(\mathrm{I_{inRMS}}\) (Figure 11a) and output current \(\mathrm{I_{out}}\) (Figure 11b). Analyzing the dependences shown in Figure 11, it can be seen that they are a decreasing function of load resistance \(\mathrm{R_{o}}\) regardless of output voltage \(\mathrm{V_{out}}\). Figure 11a shows that the highest RMS value of input current \(\mathrm{I_{inRMS}}\) equal to 0.46 A was obtained for the charging system operating with output voltage \(\mathrm{V_{out}}\) = 20 V and load \(\mathrm{R_{o}}\) = 4 \(\Omega\), while a much smaller value of \(\mathrm{I_{inRMS}}\) = 0.11 A was obtained for output voltage \(\mathrm{V_{out}}\) = 5 V and load resistance \(\mathrm{R_{o}}\) = 1 \(\Omega\). The lowest effective value of input current \(\mathrm{I_{inRMS}}\), about 50 mA, was obtained for resistance \(\mathrm{R_{o}}\) = 10 k\(\Omega\), for all three values of output voltages \(\mathrm{V_{out}}\). In Figure 11b, one can see the identical shape of \(\mathrm{I_{out}}\)(\(\mathrm{R_{o}}\)) dependence as in Figure 11a, while the values of output current \(\mathrm{I_{out}}\) are much higher than in the case of the dependence from Figure 11a. For load resistance \(\mathrm{R_{o}}\) = 4 \(\Omega\) and output voltage \(\mathrm{V_{out}}\) = 20 V, output current was equal to 4.2 A. Figure 12 illustrates the influence of load resistance \(\mathrm{R_{o}}\) on the total harmonic distortion value THD of the voltage and current drawn from the power grid (a) and the power factor PF (b) for three different values of output voltage \(\mathrm{V_{out}}\). The value of THD was calculated using Formula (1), while the PF value was calculated using Formula (4). In Figure 12a, it can be seen that, in the whole range of changes in load resistance \(\mathrm{R_{o}}\), the dependence of both the THD coefficients on \(\mathrm{R_{o}}\) is a decreasing function. It can be seen that the power network voltage \(\mathrm{THD_{V}}\) in the whole range of changes in \(\mathrm{R_{o}}\) changes only by 5%, while the value of the total harmonic content of the current \(\mathrm{THD_{I}}\) changes by as much as 18.5%.