applied sciences  
A Resonant Ring Topology Approach to Power Line Communication Systems within Photovoltaic Plants  
[PERSON]\({}^{\copyright}\), [PERSON]\({}^{\copyright}\), [PERSON]\({}^{\copyright}\), [PERSON]\({}^{\copyright}\), [PERSON]\({}^{\copyright}\), [PERSON], [PERSON]\({}^{\copyright}\), [PERSON]\({}^{\copyright}\) and [PERSON],*\({}^{\copyright}\)  
physical support of traditional PLC systems [6; 7], namely power wires with two conductors that run parallel to each other. Transmission in these kinds of lines is performed by means of TEM or quasi-TEM modes, and the traditional transmission lines theory is applicable, with of course some limitations, such as the nonuniformity of the distributed parameters. Ref. [8] presents an intelligent PV module monitoring scheme based on a parallel resonant coupling unit, which uses the DC bus as the communication channel and modulates the monitoring data into a 200 KHz carrier for communication. However, the topology of the power cables in each string of PV plants is essentially different since there is a single cable connecting the PV modules in series that runs away from other sections of the line, at least in parts of it. This part of the power line can be modelled as a single cable line, where the propagation mode cannot be TEM and where the classic transmission line theory is not applicable. This difference suggests that the optimal electronics, carrier frequencies and general strategy could be different than the ones intended for traditional PLC systems.  
This single-wire topology is imposed by the inherent characteristics of the power wiring within each PV string. As such, in this work, we propose an adapted strategy with electronics for implementing PLC communications over this cabling topology of a single PV string, where we start considering this essential difference from classic PLC standards, since the two-wire physical support common for classic PLC applications is absent in this configuration.  
One of the first studies focused within the area of single-cable transmission was performed by [PERSON] [9] in 1950, based on a previous study of [PERSON] from 1899 [10]. These studies showed the possibility of radiofrequency propagation via a surface wave guided by a single conductor, in conjunction with the formulation of a TM propagation mode for the signal. By 2008, Corridor Systems, Inc. (Santa Rosa, United States)registered a patent application [11] for a single-cable transmission line proposed for carrier frequencies from 50 MHz to 20 GHz. Later studies have been published adding updated formulations of the single-cable transmission phenomena [12] and complementing the theory with the calculation of ohmic currents' distributions, losses and characteristic impedance or even creating a classic two-wire-line equivalent model for the single-cable propagation [13]. One of the most interesting conclusions of these works is the possibility of a very-low-loss propagation over a single cable. Therefore, this study evaluates the performance and accompanying possible benefit of the propagation mode of the PV plant single-cable segment and the need for compensatory electronics to sustain the innate benefits of the behaviour of the mode in the event where the cable is altered.  
Our proposal for the PV string PLC communications system is to close the single-cable signal path by means of a capacitor connected between the combiner box terminals, in such a way that the line becomes a ring-shaped path for the communications signal, susceptible to being pushed to a loop-antenna-like resonance, improving the signal levels along the line. This work is structured as follows: Section 2 shows the theoretical frame and materials, Section 3 presents the results and Section 4 shows the conclusions and future work.