# A Power-Line Communication System Governed by Loop Resonance for Photovoltaic Plant Monitoring
## 1 Introduction
The PLC signal showcased negligible interference with the solar module MPPT operating points and inverter voltage whilst being properly detected. The PLC board of the system was however at the time of the study, 30 euros per board. Ref. [7] utilized a pulse modulation methodology at low frequency (1 kHz) for PLC communication, by using a switchable current source. The authors tested the method among four different self-built transmitter configurations and used a current transformer for sensing at the receiver, housed at the inverter. Each transmitter produced a distinct pulse and showed no alteration in features when the I-V operating point was varied, however varying PV array configurations resulted in signal attenuation either by increasing the number of modules in series (20 \(\times\) 1) or the number of strings in Parallel (5 \(\times\) 4, 10 \(\times\) 2). This performance was relative to the authors' reference configuration of 10 solar modules in series (10 \(\times\) 1). Whilst the signal strength was still favorable for the authors, the communication speed was low (about 1 kbps). Ref. [8] employed base band communication under CENELEC B band (95-125 kHz) with capacitive coupling to the power line. They used bypass capacitors across the PV modules but no AC blocking coil to prevent the communication signal from flowing through the modules. The transmission was driven by a Texas Instruments MSP430 microcontroller at 100 kHz along a simulated 1000 m string, with an inline line trap attached to filter the carrier signal to reduce harmonics at the inverter input. The PLC module configuration approximated to about 10 euros or 2% the cost of a 250 kWp solar module, significantly cheaper to [6]. The authors estimated that using RS-232/RS-485 wired or radio wireless topologies would equate to 30 and 18 euros more respectively. Ref. [5] utilized a PLC system driven by commercial PLC components as in [6], which was governed by orthogonal frequency division multiplexing (OFDM) modulation. With this setup, the authors could obtain transmission speeds up to 4000 kbps as stated in [9], due to the high-frequency band (2-30 MHz) capabilities of the components, but as in [6], the use of commercial components was expensive [10; 11; 12]. All employed PLC communication with Amplitude Shift-Keying, with [10] describing some basis for the design of a modem to employ direct current (DC) PLC. In [11], the authors proposed a grouping method for a residential PV system of four solar modules per PLC module to assess the possible cost reduction in comparison to their preliminary system of one solar module per PLC module in [9]. The new configuration gave rise to a 72% cost reduction; however, with this setup voltage becomes the only differentiating variable at the solar module level. Their PLC system was driven by a 16-bit MCU with the use of capacitive coupling as in [8]. In [12] the PLC system was dictated by parallel resonant coupling through LC resonators and driven by a 32-bit MCU. The system was tested along a 16 solar module string, with modules each of 255 W. A 200 kHz pulse width modulated (PWM) carrier wave was generated and used from the MCU. The wave was transformed to a sinusoidal waveform through an m-derived low pass filter designed to filter three levels of harmonics. The MCU then applied digital switching to modulate the wave. Within this study, the authors demonstrated a sizable increase in transmission efficiency when using their coupling circuit in comparison to conventional capacitive coupling as found in [8; 9]. This gain in performance was especially identifiable as the impedance of the coupling circuits were increased. The authors also compared the output signal strength of both coupling methods by validating against the open circuit output signal of a coupling circuit. Within this test, very little signal reflection/attenuation was recorded during transmission when using parallel resonance relative to capacitive coupling. Above all else, the estimated cost of the PLC board equated to 5 USD/4.52 EUR per board.