Full Wireless Distributed and Redundant Control of Solar Trackers

During the last years PV plants tend to incorporate full-wireless and other systems that secure the installations and contribute to the customers’ trust. The objective of these systems is to anticipate adverse meteorological phenomena with greater precision and be prepared for the defense position or communicate a problem in the plant with greater speed and precision.

October 13, 2020. By News Bureau

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With operations and subsidiaries in the five continents, Soltec leads the solar PV market at the Latin American continent with more than 7 GW of solar trackers supplied.

Soltec has recently released its latest generation of Trackers Control System.The new development is a comprehensive solution which integrates a new ecosystem of devices.

The main features of this new control system are:

Full Wireless Communications using OpenThread_{(released by Google)} technology and MQTT
protocol.
High availability with the self-healing mesh network, redundancy of all devices and no
single point of failure.
Auto-Commissioning procedure for setting up and test Trackers automatically.
Super-fast installation of devices to structure.
Double life expectancy of batteries using LiFePO₄technology.
Encrypted communications and individual identification, authentication and
authorization of all users or devices with access to the network.
Full functional mobile APP for O&M purposes through NFC interface

OpenThread_{(released by Google)} is an open-source implementation of Thread^®. Thread is a low-power wireless mesh networking protocol designed for easy integration in the connected environments. Being an IP-based open standard, Thread allows smart devices to connect directly securely and reliably to the cloud. OpenThread solves the problem of communicating safely and securely tens of thousands of devices spread in large PV plants without the need of adding repeaters.

Figure 1 - Thread Mesh Network with Trackers

The main components of the new communications and control system are the Tracker- Control-Box and the Gateway Control Units.

Tracker-Control-Box: A new enclosure which clamps to the tracker’s structure in record time and can be installed by only one person. The battery compartment is independent from the electronics circuits, allowing a secure and safe replacement. The main body is made of aluminum, having a direct thermal contact from the power electronics to the body. This new feature ensures the internal temperature of the electronics devices, keeping them cooler than in previous designs, a feature that directly enhances the life expectancy of the internal components.

Figure 2 - Tracker-Control-Box

Inside the Tracker-Control-Box the two main electronics boards are connected board to board in a “sandwich” fashion, this feature reduces the volume needed inside the box while improves the manufacturing time. This “sandwich” of circuits can come out of the box as a package in case of replacement of inspection tasks. The two mentioned main boards are the Tracker-Controller-Unit (TCU) and the Serial Power Supply (SPS).

Tracker-Controller-Unit (TCU): A new controller designed from scratch which breaks with the previous generations as it uses the latest technologies on the market. The main microcontroller has been replaced increasing the performance and memory and allowing new smart features like self-diagnostic with full reports, self calibration and auto-commissioning to name some of them. This new controller integrates our patented Over-Angle-Detector (OAD) for redundant security and a high accuracy current sensor for preventive maintenance analysis.

Figure 3 - Tracker-Controller-Unit

Serial Power Supply (SPS): The next generation of our patented serial power supply which charges the battery pack from the current that flows through the existing strings over the tracker. This new generation improves the power conversion efficiency and is compatible with a broad range of battery technologies, including LiFePO₄ cells. One of the most important features is the automatic string/panel mode which ensures the battery pack will be kept in a good state of charge independently of the string status. This feature switches from string to panel mode in case the string is not working for some reason like inverter maintenance, problems with the transformers or grid connection, fuses, or connections problems. The new SPS integrates a new digital control allowing the monitorization of all the internal parameters and being able to be updated over-the-air.

Figure 4 - Serial-Power-Supply

Gateway-Control-Unit (GCU): Each subfield of trackers is controlled by a single GCU which integrates a powerful embedded computer, three independent OpenThread interfaces, RS485 interface for sensors, GNSS connection for position and time synchronization, GPRS communications and USB ports and SD card slot for mass storage.

The new mesh communications are interfaced with the OpenThread modules and the newGCU incorporates three of them. The #1 OpenThread interface labeled as “Ant 1” is the main interface for communicating with all the trackers assigned inside the subfield, the other two interfaces “Ant 2” and “Ant 3” are available for redundant features. In case one GCU becomes unavailable, the closest ones will assume the control over the trackers, maintaining all the trackers available with double GCU redundancy.

Figure 6 - GCUs Redundancy

The GCU software runs over Linux O.S. and offers a comprehensive HMI allowing configuration and monitorization of all the parameters related to the GCU and all the TCUs assigned.

At the “cold-commissioning” stage of the plant installation, the new GCU is able to set up the whole subfield with independence of the status of the rest of the plant (plant network, energization, inverters, etc). The time is synchronized through its GPS interface and the meteorological measurements are performed directly at the GCU with the corresponding sensors connected (wind, snow, flood, temperature, etc). The standard interfaces between the trackers network to third party SCADAs are MQTT and OPC-UA, having an OPC-UA server at each GCU.

- José Alfonso Teruel, CTO, Soltec Innovations