PRAKTISCH: Test Bench-Based Characterization of Grid-Forming Properties of Type III Wind Turbines

At a glance

• As part of the energy transition, large synchronous generators of fossil-fuel power plants directly connected to the grid will be phased out. Wind turbines, among others, will have to take over the task of forming the grid. However, there is a lack of generally and internationally accepted regulations and processes that qualify them for this task.
• The PRAKTISCH research project is developing a technology-neutral validation process that can be used to clearly measure, test on test benches, and certify the grid-forming behavior of wind turbines.
• In addition to project coordination, Fraunhofer IWES is responsible, among other things, for preparing and implementing the test campaigns on the institute’s own test benches.

The challenge

The transition of the energy system to renewable energy is also shifting responsibility for the safe operation of the power grid. Until now, voltage and frequency stability has been ensured primarily by the large synchronous generators of fossil-fuel power plants connected directly to the grid; however, these are gradually being decommissioned. In the future, this task must be taken over, among other things, by wind turbines connected to the grid via power converters. When using the currently standard control methods, they are unable - due to their grid-feeding characteristics - to maintain a grid with 100 percent renewable energy without synchronous generators, i.e., to exhibit so-called grid-forming behavior.

Existing control methods capable of solving this problem have so far found little application outside of research and development work. For example, there is no generally and internationally accepted definition of grid-forming behavior and thus no basis for certification. Consequently, there is considerable uncertainty regarding future grid-forming requirements for wind turbines.

The solution

This is where the PRAKTISCH research project comes in. The scientists are developing a technology-neutral validation process for wind turbines that allows their grid-forming behavior to be clearly and quantitatively measured and characterized at their grid connection point. Despite the technology-neutral approach, particular attention is being paid to Type III wind turbines, which feature a double-fed induction machine and thus a direct electrical coupling between the generator and the grid.

The plan is to conduct test bench-based validation and characterization of various grid-forming wind turbines to experimentally demonstrate the process. The validation of the test bench measurements is achieved by reproducing field measurements of a grid-forming wind turbine. The applicabilityof the process is finally demonstrated by an exemplary certificate or a declaration of conformity from a certification body.

In addition to project coordination, Fraunhofer IWES is responsible, among other things, for the preparation and implementation of the test campaigns on the institute’s own test benches, HiL-GridCoP and PQ4Wind.

The added value

PRAKTISCH demonstrates a test bench-based validation process as the foundation for the standardized measurement and certification of grid-connected wind turbines. This process will provide recommendations for turbine manufacturers, wind farm-, grid-, and test bench operators, as well as certification bodies. At the same time, it recommends a reliable procedure for standardizing product requirements, test methods, and evaluation criteria. The project results will be presented to German, European, and other international standardization bodies.

PRAKTISCH thus contributes to the safe operation of the power grid, which is primarily supported by decentralized generation plants and storage systems.