# Influence of Random Modulated Power Converter on G3 Power Line Communication
## 5 Results and Discussion
### Effects of the Converter Switching Frequency  
This section presents experimental results showing the effects of the switching frequency of a randomly modulated power converter on the G3-PLC system. Hence, different switching frequencies from 10 kHz to 100 kHz are considered for this analysis. Figure 6 shows the FER calculated from 3000 frames of data transmitted through the G3-PLC when different switching frequencies are applied to the DC-DC converter resorting to RPPM. The input of the DC-DC converter is fixed to 50 V. The FER is significantly higher in the G3-PLC bandwidth (when the switching frequency of the DC-DC converter is in the range of 35-91 kHz), with a maximum value of around 60 kHz (i.e., the center frequency of the PLC bandwidth). However, the FER is not significant where the switching frequency of the DC-DC converter is out of the bandwidth of the G3-PLC. This result allows draws the conclusion that RPPM could only influence the G3-PLC when the switching frequency of the power converter is in the bandwidth of the G3-PLC system. Figure 6: FER of the G3 PLC vs. switching frequency of the DC-DC converter modulated with RPPM. A similar analysis involving RFM was carried out in [14], with the same input voltage of the DC-DC converter (50 V), and switching frequency varied from 50 to 75 kHz. Some of the results obtained in [14] are summarized in Table 3. The comparison allows appreciation of the fact that RFM (with 15-30% modulation index) causes significantly larger FER (more than 40%) compared to RPPM, with a maximum FER of 8% obtained at 20% modulation index (which is the maximum possible pulse position variation, as defined in (9)) around the intermediate switching frequency (60 kHz). Even with lower modulation indexes, RFM causes higher FER than RPPM. This is because the bandwidth of the noise generated by a DC-DC converter with RFM is wider (i.e., the noise is more spread) than with RPPM. This can be easily appreciated in Figure 7, where the CE exiting the same DC-DC converter driven by different modulation schemes (PWM, RFM, and RPPM at the 20 kHz switching frequency) are compared. The comparison unveils that even if RFM is more effective than RPPM for EMI reduction, RPPM offers significant advantages in terms of coexistence with communication systems. Of course, better performance of RFM can be obtained by adjusting the working parameters, i.e., by reducing the modulation index of RFM it is possible to have lower interference to the G3-PLC, but with lower CE reduction. This corroborates the conclusion that choosing the right modulation scheme is to be intended as a trade-off between EMI reduction and the coexistence issue. This conclusion is also confirmed when the Channel Capacity is considered. As depicted in Figure 8, the Channel Capacity of the G3-PLC reduces when the switching frequency of the converter is near the intermediate frequency of the G3-PLC system. However, for switching frequencies out of the bandwidth of the G3-PLC,  
Figure 7: Comparison of the CE exiting the same DC-DC converter driven by different modulation schemes. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Frequency (kHz)**} & \multicolumn{5}{c}{**G3-PLC Performance**} \\ \cline{2-7}  & \multicolumn{2}{c}{**FER (\%)**} & \multicolumn{2}{c}{**Channel Capacity (kb/s)**} & \multicolumn{2}{c}{**Channel Capacity Loss (\%)**} \\ \cline{2-7}  & **RFM** & **RPPM** & **RFM** & **RPPM** & **RFM** & **RPPM** \\ \hline
60–63 & 50 & 8 & 390 & 498 & 48 & 18 \\
50 & 8 & 5 & 460 & 515 & 40 & 16 \\
75 & 4 & 3.5 & 370 & 503 & 50 & 17 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Comparison of the performance of G3-PLC assessed with RFM and RPPM applied to the DC-DC converter [14]. not significantly affected.