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Case studies

Monitoring and control of FVE Dobšice

Although it would seem that photovoltaic plants have in principle the same design and their control systems are therefore one after the other, this may not always be the case. Interesting exceptions are installations where several types of devices from different manufacturers have come together - whether they are panels, inverters or communicative modules for measuring string currents. In these cases, the advantage is a freely programmable control system, which can be adapted to the requirements of the designer during commissioning. Then the result is an installation that responds precisely to the surrounding conditions and requirements of the distribution network, while guaranteeing the maximum possible production and thus profit.

An example is FVE Dobšice u Znojma. 10 investors participated in the set of photovoltaic power plants in Dobšice. Their installations are technically separate, however the power plant is connected to the network as a whole, with a common RTU unit for active limitation and reactive power control. A total of 116 inverters of 8 different types are used in ten sections with different outputs from 6.5 to 1020 kWp, some without the possibility of software power limitation by means of bus communication. The supplied Domat control system with six IPLC510 substations had to solve a "fair" control of active and reactive power between investors, which was successful thanks to extensive communication options and freely programmable substations. In the case of non-adjustable inverters, the distributions on the AC side are divided into groups that can be switched off by contactors. The contactors are controlled by output modules that communicate with the controllers via the Modbus RTU bus.

investor type of inverters pcs total power (kWp) type of regulation
1 - WEB Kaco

33

1020,6

communication
2 - JS Kaco

7

233,1

communication
3 - MH Kaco

3

99,9

communication
4 - JH Dop Kaco

8

207,85

communication
5 - Alpha Solarmax

4

76,55

contactors
6 - Beta Solarmax

3

105

contactors
7 - Gamma Solarmax

3

105

contactors
8 - Delta Solarmax

4

140

contactors
9 - Sinus Net Solarmax

2

6,55

contactors
10 - Arctur Solarmax, SMA, Refusol

49

922,15

communication, contactors

Overview of inverter groups and control methods.

Seven IPLC510 substations are interconnected by a technological network. The optical backbone network is resistant to interference, which is abundant in photovoltaic power plants. The Moxa EDS-205 switches provide 5 Ethernet ports in each cabinet, which is sufficient for both process controllers and inverter interfaces (SMA Webbox) and diagnostics and service. The entire power plant has a common computer with a graphical interface, which can be accessed remotely by the service company and individual investors, each under their own name and password only to their part of the power plant.

The control algorithm is thus able to meet the requirements of the distributor and at the same time divide the disconnected power evenly between all 10 sections of the power plant. Monitoring then monitors the correct function of the inverters and panels and reports faults so that the service organization can react in time and the delivered power is as high as possible. FVE Dobšice has actually become a living model of a virtual power plant, ie a distributed system of mutually independent energy sources, which, however, need to be managed and monitored as a whole with a common interface for the distributor - customer.