Photovoltaic power plant control with UniPi programmable logic controllers

References

Imagine a system that can allow you to control multiple large solar power plants on two different continents from a single control centre and with minimal personnel requirements.

The Photon Energy company based in Amsterdam provides complex services in the field of solar power plants, including the planning, monitoring and maintenance. Currently, the company operates more than 100 ground-based solar systems in six countries with a total power output of 50MWp. Control and monitoring of such extensive installations require reliable controllers with large computing power. Photon Energy representatives thus contacted the development team of UniPi.technology.

The company issued a technical specification for a development of custom controller compliant with the next-generation requirements; Photon Energy requested the controller to feature high CPU power, four RS485 serial interfaces, 8GB internal memory for data storage and I/O modules. These requirements had to be combined with the PECOM communication and monitoring interface developed by Photon Energy.

The UniPi Axon S115 controller was used as a basis for the custom development. This controller features four RS485 serial interfaces, allowing it to communicate with a large number of external devices. Aside from the standard equipment, Photon Energy also requested the implementation of the HUB function for aggregation of data, its transformation and transmission to the PECOM system. The resulting product was designated as Commander PE115S; both the controller and the paper packaging feature custom colour and Photon Energy company logo.

The customized controller enhanced the previous functionality by the option to run applications with higher computing power requirements (PECOM system) and also allowed the reduction of the number of devices placed in distribution boxes.

PECOM system user interface

Specialized models

S115 is not the only specialised Axon model in the UniPi line-up. Included in the brand-new UniPi Axon product line are also Axon S205 and Axon S505 models, both featuring an architecture focused on specific automation tasks.

The above-mentioned Axon S115 is suitable for the use as a communication hub for a large number of devices thanks to its four RS485 serial lines. The controller can communicate with up to 100 devices and can be used for creating extensive automation networks. When combined with the Neuron xS extension modules, you can create a network of up to 2880 I/Os. Aside from the RS485 interface, the controller also features a single RS232 serial line and a 1-Wire bus for connecting various simple sensors (thermometers, humidity meters etc.)

The Axon S205 features 8 digital inputs and 8 relay outputs. Digital inputs are designed for reading binary logic states manifested by voltage level, allowing the controller to receive data from binary devices such as lighting switches, water level sensors, motion sensors etc. Inputs can be also connected to an S0 output of various pulse meters (energy meters, water flow meters, gas flow meters etc.) for medium consumption monitoring. Relay outputs are then used for switching two-state devices with a higher current consumption such as light bulbs, pumps, boilers or larger external relays. The resulting combination is suitable for lighting control, remote door control, automated irrigation systems and other similar applications. The controller also features a single RS485 serial line and a single 1-Wire bus.

The Axon S505 is provided with four analogue inputs and four analogue outputs, allowing it to read values from analogue sensors such as tensiometers or pressure meters. Inputs of the S505 can be also used for current or voltage measurements and also support the resistance measurement to read data from resistance thermometers. Analogue outputs then serve for regulation of multi-state devices by 0-10V voltage. The S505 is a good choice for regulation of multi-state valves, lighting dimmers, actuators, servo motors etc. The RS485 serial line and the 1-Wire bus are retained.

All mentioned models share basic features common to all UniPi Axon models. Axon controllers are powered by an industrial computer with 1.2GHz quad-core ARM CPU and 1GB RAM and feature an 8GB eMMC onboard memory. By default, all Axons also feature a single 1Gbit Ethernet and a pair of USB 2.0 ports.