Intelligent control technology compensates for power dissipation Reactive power no longer has to be purchased
In certain constellations, photovoltaic systems also generate capacitive power dissipations through the night. To ensure that reactive power does not have to be purchased from the grid operator in such cases, Phoenix Contact has developed the Q@Night control function, which is already in use in a PV park in Saxony-Anhalt, Germany.
ASG Engineering GmbH, based in Saxony-Anhalt, Germany, was founded in 2007 and specializes in consulting, planning, implementation, and operational management of photovoltaic systems.
Their range of services also includes integrating systems and storage systems into the existing infrastructure to ensure the optimized use of self-consumption. In addition, the company also specializes in peak shaving and storage solutions for micro-grid systems.
This project is a 10-megawatt PV park at the Dessora Industrial Park in Oranienbaum-Wörlitz in eastern Saxony-Anhalt, Germany.
Before the electricity can be fed into the grid, it must first be transmitted to the grid connection point three kilometers away via underground cabling. Due to the long cable length, capacitive power losses occur, particularly at night. The transformers in the park also generate losses, in this case inductive power dissipations. Normally, the park operator would have to purchase reactive power from the grid operator to compensate for such power dissipations. The financial cost of such purchases would add up to a mid-range five-digit amount over the course of a year.
The Phoenix Contact feed-in controller based on PLCnext Technology is installed at the grid connection point. This device, certified in accordance with the German Directive VDE-AR-N 4110/4120, ensures that decentral power generation plants that are connected to medium and high-voltage grids feed in electricity in accordance with the grid requirements.
Since the hardware and software of the feed-in controller can be adapted individually and project-specifically at any time, the device can be expanded to include the Q@Night control function. The term Q@night comes from the concept of reactive power control at night. The Q@Night controller function programmed by ASG Engineering and integrated into the Power Control Unit ensures that the inverters in the photovoltaic park do not shut down during the night, as is normally the case. Instead, they continue to provide reactive power in order to achieve a phase shift of precisely cos hi = 1 at the grid connection point. In this way, the inductive and capacitive properties of the park equipment – i.e., cables and transformers – are balanced.
The specifications for the inverters installed in the field come from the bus coupler
The control signals for the Q@Night control function are forwarded via a fiber-optic cable to an Axioline F BK ETH bus coupler, which is installed in one of the four transformer stations in the PV park three kilometers away. RS Uni modules are aligned with the bus coupler and allow I/O devices with a serial interface to be operated on the bus system. The inverters, which are connected in a star configuration in 16 strings, receive the instructions required for both feed-in control and reactive power control at night from the bus coupler via RS485 data communication.
The Q@Night controller function implemented on the feed-in controller avoids the costly additional purchase of reactive power. The open control platform enables fast and reliable engineering as well as project-specific adjustments.