# A Power-Line Communication System Governed by Loop Resonance for Photovoltaic Plant Monitoring
## 5 Conclusions  
After the analysis of previous works about PV PLC communications we found two main coupling methods for injecting the signal in the power line:  
Capacitive: where the Transceiver is connected in parallel with the PV module and the signal is coupled to the line through a capacitor. Inductive: where a transformer is usually connected in series with the PV module and the signal is coupled inductively. In the first case, some of the proposals ignore the connection of an AC blocking coil in series with the PV module, and this leads to the signal flowing across the PV module, and the AC impedance of the communication path to depend on the working point of the module. In the maximum power point, a module is just between the region of very high dynamic impedance (the upper flat part of the curve) and very low dynamic impedance (the quasi-vertical part on the right of the curve), and any deviation or asymmetry in one module can push the working point to the second region, and the corresponding transceiver will be short-circuited, preventing the communication to work. If a blocking coil is mandatory to solve this problem (in parallel capacitive coupling) and a transformer is connected in series for inductive coupling, we will have the entire DC string current flowing through a coil in both cases, and with it the aforementioned saturation problem. The first novelty presented in this paper is the anti-saturation coil, that affords our circuitry the ability to overcome the drawback above described in a very simple way, without the need of venturing into the use of special or big (and expensive) coil cores. This technique is even applicable to some of the literature configurations that initially ignored the saturation issue. The other main novelty is to take advantage of the ring topology established, closing the AC signal path to work in a spatial resonance condition as described in our previ \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Author** & **Cost per PV Module** & **Carrier Frequency** & **Bitrate** \\ \hline [PERSON] et al. [6] & 30 Eur & 132.5 KHz & n/a \\ \hline [PERSON] et al. [7] & \textgreater{}25 Eur (*) & 1 KHz & n/a \\ \hline [PERSON] et al. [8] & 10 Eur & 100 KHz & n/a \\ \hline [PERSON] et al. [5; 9] & \textgreater{}25 Eur (*) & 2-30 MHz & 4 Mbps \\ \hline [PERSON] et al. [12] & 5 Eur (**) & 200 KHz & 10 Kbps \\ \hline [PERSON] et al. [14] & \textgreater{}70 Eur (*) & n/a & n/a \\ \hline Proposed method & 12 Eur & 1 MHz & 200 Kbps \\ \hline \hline \end{tabular} (*) Not specified. Estimated from the components described. (**) Coupling coil needed in series with the string, possibility of saturation.  
\end{table} 
Table 2: Comparison of the different PV PLC systems found in the literature with ours regarding the cost and communication speed achieved. ous work [16]. This topology improves drastically the communication signal levels and considerably reduces the differences between them found in open lines. Based on these two main improvements, we have designed and successfully tested a very simple and low-cost hardware that improves upon most of the communication speeds previously reported with a cost lower than most of the previous works analyzed (Table 2). Conceptualization, J.I.M.-A., V.A.-G. and L.H.-C.; methodology, J.I.M.-A., V.A.-G. and L.H.-C.; software, J.I.M.-A. and M.S.M.W. ; validation, J.I.M.-A., H.K. and M.S.M.W. ; formal analysis, J.I.M.-A., V.A.-G. and L.H.-C.; investigation, J.I.M.-A., V.A.-G. and L.H.-C.; resources, J.I.M.-A., [PERSON], [PERSON], H.K. and [PERSON]; data curation, [PERSON]-A.; writing--original draft preparation, J.I.M.-A., H.K. and M.S.M.W. ; writing--review and editing, [PERSON] and [PERSON]; supervision, [PERSON] and [PERSON]; project administration, [PERSON] and [PERSON]; funding acquisition, [PERSON]C. All authors have read and agreed to the published version of the manuscript. This research was funded by the Universidad de Valladolid with the predoctoral contracts of 2020 cofunded by Santander Bank.