Non-Adaptive and Adaptive Coupling Circuits for Power Line Communication System

Abstract

This work outlines a comprehensive review of PLC coupling circuits, which are required for narrowband and broadband PLC transceivers. Prevailing issues that protract the design of couplers and consequently subtended the inventions of different types of couplers are clearly described. Also, it provides a useful classification of PLC couplers based on the type of physical couplings, voltage levels, frequency bandwidth, propagation modes and a number of connections. Next, the focus is on the design of non-adaptive capacitive, SISO and low-voltage (LV) PLC coupling circuits for both broadband and narrowband applications. The narrowband cover the frequency band 9 kHz-500 kHz, while broadband frequency bands are 1.7-50MHz, 1.7-100MHz and 1.7- 500 MHz. Moreover, it discusses the specification and design of the prototypes of the PLC coupling circuits measuring their scattering parameters. The access impedance of Brazilian in-home, broadband and low-voltage electric power grid in the frequency band 2-500 MHz is taken into account. Based on the use of a measurement setup a large measurement campaign that was carried out in several facilities in three different Brazilian cities is discussed. Also, a procedure to obtain a statistical model of the access impedance in the aforementioned broadband frequency is outlined. Based on a number of measured access impedances and well-known criteria for choosing statistical models, two distributions to model the resistance and reactance components of the access impedance are suggested. Due to the fact that the parameters of such models change with the frequency and the access impedance is a random process in the frequency domain, a simple and effective model to generate samples function of such random process, which takes into account the suggested distributions, is addressed. Finally, adaptive capacitive, SISO and LV PLC coupling circuits are proposed for broadband power line communication. These adaptive coupling circuits use three different analog low-pass filter for impedance matching. This filter is an array of analog low-pass irregular filters that separate the input and output signal into three analog low-pass filters, each one matching the impedance between the electric power grid and PLC transceiver. The input impedance of each filter has a different impedance value, chosen according to the impedance of the measurement campaign, and the output impedance is fixed in 50 Ω for all analog low-pass filter. The choice of the analog filter that provides better impedance matching to the electrical power grid is obtained by a microcontroller, which through an analog-to-digital converter (ADC), measure the voltage provided by a circuit that measures the power of the signals injected into the PLC coupling circuit by the PLC transceivers. The power is continuously measured by an ADC of the microcontroller which chooses which analog filter provides the best impedance matching with the electric power grid and switches the analog filters through an analog switcher connecting the PLC transceivers to the electric power grid through the PLC coupling circuit. In addition, the measured values of the scattering parameter S11 show that the best impedance matching occurs when the resistive impedance component of the access impedance is between 50 Ω and 100 Ω . For the scattering parameter S12 it has been found that the attenuation increases as the frequency increases because of the inductive behavior of the electric power grid.