The increase in electricity generated from renewable energy has a major impact on the electrical grid. Wind turbine generators feed the electricity into the grid via power-electronic converters. Therefore, validation of system characteristics and the grid-supporting performance of wind turbines are becoming increasingly important for grid stability.
The so-called fault-ride-through capacity of a wind turbine to not detach itself from the grid during sudden voltage drops or voltage peaks in the electricity grid (FRT), the provision of reactive power supply or the compensation of frequency deviations are some of the requirements to be met by wind turbines. Evidence of these features in new turbines must be provided during the development process and market launch of wind turbines. In the past, manufacturers have provided evidence of these properties with a complex measuring routine on prototype turbines in the field.
The Fraunhofer-Institut für Windenergiesysteme (IWES) in Bremerhaven, Germany, and the Nordex Group have developed a new approach. As part of a research project, a hardware-in-the-loop test bench was created over a period of three years. On the test bench, the electric drive train of the wind turbine is tested in isolation on a grid simulator. The big advantage is that all other components of the wind turbine are simulated in real time and the test bench can of course be operated regardless of the weather. A first generator and converter configuration has already been successfully tested and certified “in the laboratory.”
“Field validations of turbine system properties are necessary but time-consuming,” says Michael Franke, vice president of global engineering at the Nordex Group. “Added to this is the difficulty of finding a suitable site for the test series. Measurement of the electrical grid properties of a turbine in the field takes more than 12 months until certification. The same test on the IWES test bench has now been completed in three months – a saving of nine months. This test bench represents a major step forward for both partners as it makes a faster time to market possible.”
“Thanks to its flexibility and functionality, the test bench is also ideally equipped for the expected future requirements for verification,” adds Prof. Dr.-Ing. Andreas Reuter, director of Fraunhofer IWES.
IWES and the Nordex Group plan to further intensify their collaboration in the form of follow-up projects.