## 4 Results of Measurements
The highest value of the \(\mathrm{THD_{I}}\) was obtained for the considered system operating with output voltage \(\mathrm{V_{out}}\) = 20 V (\(\mathrm{THD_{I}}\) = 92% @ \(\mathrm{R_{o}}\) = 4 \(\Omega\)), while the lowest value of the \(\mathrm{THD_{I}}\) was obtained for the tested system operating with \(\mathrm{V_{out}}\) = 5 V (\(\mathrm{THD_{I}}\) = 73.4% @ \(\mathrm{R_{o}}\) = 1 k\(\Omega\)). In Figure 12b, it can be seen that the biggest changes in the power factor value were observed for load resistance \(\mathrm{R_{o}}\) changing in the range from 1 to 10 \(\Omega\). The highest value of the power factor PF = 0.95 was obtained for the charging system operating with load resistance \(\mathrm{R_{o}}\) = 4 \(\Omega\) and output voltage \(\mathrm{V_{out}}\) = 20 V. For the load resistance \(\mathrm{R_{o}}\) in the range from 1 k\(\Omega\) to 10 k\(\Omega\), the power factor stabilizes at a value of about 0.8. Figure 13 illustrates the influence of load resistance \(\mathrm{R_{o}}\) on energy efficiency \(\mathrm{\eta}\) of the tested EVLONE140W system for three different values of output voltage \(\mathrm{V_{out}}\). The value of \(\mathrm{\eta}\) was calculated using Formula (2). In Figure 13, it can be seen that the dependence of energy efficiency \(\mathrm{\eta}\) of the tested system is a decreasing function of load resistance in the whole range of \(\mathrm{R_{o}}\) changes regard  
Figure 13: Calculated dependence of the energy efficiency on load resistance. less of output voltage V\({}_{\text{out}}\). With an increase in the output voltage, the energy efficiency increases. Its highest value \(\eta\) = 91.9% was obtained for V\({}_{\text{out}}\) = 20 V and R\({}_{\text{o}}\) = 4 \(\Omega\). In Figures 11-13, it can be seen that, at higher values of the output voltage, higher values of the energy efficiency and the input and output current were obtained. The energy efficiency was higher in the range of low values of load resistance. At high values of load resistance, PF values practically did not depend on the value of V\({}_{\text{out}}\) voltage. Figures 14 and 15 present the influence of load resistance (Figure 14) and the output voltage (Figure 15) on the waveforms of input current I\({}_{\text{in}}\) drawn from the power grid by the tested system. Experimental studies were carried out for the power grid voltage V\({}_{\text{inRMS}}\) = 230 V. Figure 14 presents the studies carried out for two different values of load resistance R\({}_{\text{o}}\) equal to 10 \(\Omega\) and 1 k\(\Omega\), respectively, and for output voltage V\({}_{\text{out}}\) = 20 V.  
In Figure 14a, it should be noted that the highest peak-to-peak value of input current I\({}_{\text{inpp}}\) = 0.82 A was obtained for load resistance R\({}_{\text{o}}\) = 10 \(\Omega\), and the lowest value I\({}_{\text{inpp}}\) = 0.16 A for load resistance R\({}_{\text{o}}\) = 1 k\(\Omega\). In turn, in Figure 14b, it can be observed that the highest normalized values of the harmonics in the spectrum of current I\({}_{\text{in}}\) were obtained for R\({}_{\text{o}}\) = 10 \(\Omega\). During the tests, up to 15 harmonics with the maximum normalized value were recorded, which confirms the high level of distortion of current I\({}_{\text{in}}\). In turn, for  
Figure 14: Measured waveforms (**a**) and the spectrum (**b**) of input current I\({}_{\text{in}}\) for different values of load resistance. Figure 15: Measured waveforms (**a**) and the spectrum (**b**) of the input current for different values of the charging system output voltage. the considered values of load resistance, only the first and second harmonics with the maximum normalized value could be observed, and higher harmonics had an increasingly smaller amplitude. Figure 15 presents the test results carried out for two values of output voltage V\({}_{\text{out}}\) equal to 5 and 20 V, respectively, and for load resistance R\({}_{0}\) = 10 \(\Omega\).