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Communication between string inverters and the monitoring system is crucial in photovoltaic plants to optimize the performance of the installation. Two common methods for this communication in industrial installations are PLC (Power Line Communication) and RS485. PLC uses existing power cables to transmit data, while RS485 requires dedicated cables for data communication. This article explores the characteristics, advantages, and disadvantages of communication via PLC.

Power Line Communication (PLC) allows data to be transmitted through the same cables that carry electrical power. This is achieved by adding another frequency-modulated wave containing the information to be transmitted to the AC power signal (carrier signal).

Ilustración 1. Signal summation.

The connection scheme for systems using PLC is as follows:

Ilustración 1. PLC Communication Diagram HUAWEI SUN2000.

The signal is transmitted through the power cable to the transformation centers, where the information is extracted from the power cables and sent to the plant’s control system.

The connection scheme for systems using RS485 is as follows:

Ilustración 1. RS485 Communication Diagram HUAWEI SUN2000.

Advantages of PLC Communication:

Reduction of Cabling: By using existing power cables, PLC eliminates the need to install additional cables for data communication, reducing costs and simplifying installation..

Simplification of Installation: Using already installed power cables facilitates the implementation of communication, especially in large and complex projects.

Adaptability: PLC can be used in a variety of configurations and can adapt to different network architectures without significant infrastructure changes.

Disadvantages of PLC Communication:

Interference and Noise: Data transmission through power cables can be susceptible to electromagnetic interference and noise, which can affect the quality and reliability of communication. Certain considerations are necessary when installing the cables. For example, in the case of unipolar cables, a bundling of the tripolar cable set must be performed every meter to ensure continuous impedance in the line, as well as respecting certain distances between power circuits, which may result in slightly larger ducting than necessary.

Ilustración 1. Bundling of unipolar cable set

Bandwidth Limitations: Although PLC has improved over time, its bandwidth and transmission speed may be lower compared to RS485.

Equipment Compatibility: Not all inverters and monitoring equipment are compatible with PLC, which may limit its applicability in certain projects.

Distance: The maximum communication distance for unipolar sets is usually around 400 m, while the RS485 system can transmit up to distances of 1000 m without the need for signal repeaters.

At MEP Projects, we are familiar with these communication systems and can offer solutions tailored to your specific needs.

Made by José María Calurano (EICA Design Engineer)