Whether environmental or grid-side influences or even interactions between systems are involved, the high-performance electronics in wind turbines – onshore as well as offshore – are exposed to particularly high stresses. In order to be able to precisely research the influence of climatic and electrical loads on the complex electronics and their service life under realistic conditions, a corresponding test and experimental facility is currently being built at the University of Bremen. The Institut für elektrische Antriebe, Leistungselektronik und Bauelemente (IALB) at the University of Bremen and the Fraunhofer Institute for Wind Energy Systems (IWES) in Bremerhaven are involved in this joint project entitled “Multidimensional loads on the high-performance electronics of wind turbines” – known as “HiPE-WiND”. The German Federal Ministry for Economic Affairs and Energy is supporting this research project with around 11.5 million Euros (funding code 0324219A/B). FREQCON applied as a supplier for a complete test bench in the form of a power electronic load system as part of a call for tenders from the University of Bremen and was awarded the contract for the collaboration.
Loading system consisting of 4 units of the same type
In the future, current or newly developed converter systems of wind turbines can be comprehensively tested under precisely defined environmental conditions, such as extreme temperature fluctuations, strongly changing humidity as well as condensation, at the University of Bremen in a climate cabin designed for this purpose with a usable test space of about 171 m3 (dimensions: 5.3m x 4.3m x 7.5m). In addition, it will also be possible to closely examine interactions between the various mechatronic powertrain systems as well as network loads caused by voltage or current surges. For this purpose, this loading system from FREQCON is equipped with all the necessary functionalities and is more scalable in terms of power and operating voltage. Our task was to design and install a complete test stand – a power electronic load unit – including the accessories for testing the frequency converters used in wind turbines with outputs from 300 kW to
10 MW, and to commission it soon. Our load system simulates both the behavior of the wind turbine generator with frequencies from 0 to 70 Hz and the power grid. In order to be able to flexibly provide the required power range of possible test objects, the system has to consist of four units of the same type, each with an output of 2.5 MW. These units are able to load the test objects with the required power by connecting them in parallel. A special requirement was that the converters on the grid side and the converters on the generator side must each act synchronously.
6 kilometers of cable and 104 control cabinets
The starting signal for implementation was given directly after the kickoff meeting with all project managers at the University of Bremen in November 2019: The plant was designed on the basis of the specified requirements and largely prefabricated in Rethem. In addition, some preparatory work was necessary before the loading system could be installed in the research hall of the IALB: A cooperation partner erected an elaborate steel construction platform with 2 floors in coordination with us, which was necessary due to the confined space conditions. In addition, our installation team laid around 6 km of cable and set up 104 control cabinets in which the converter technology for the test stand is installed. Shortly before the end of the year, the test for the functionality of the systems could also be carried out. All in all, a tight program on site in Bremen, which was completed in only 9 weeks. Now the integration and testing of the hardware and software systems as well as the installation of the cooling system will take place in the next few weeks. As soon as the acceptance of the plant has taken place, the test stand can start its work. This is expected to be in June 2021.
Simulation of the service life
The researchers’ goal is to examine the converters under reproducible, combined climatic and electrical load conditions. The failure mechanisms identified in this context are to be researched and concepts for optimizing robustness are to be developed and verified. Another goal is the development of models for the accelerated aging of all converter components in the test laboratory and thus the accelerated analysis of the system service life. In this way, it should be possible to simulate the complete service life of 20 years in just a few 1,000 hours. Based on the results, it should be possible to identify weak points early on in development, develop concepts for robust components, extend the operating life of the electronics and prevent operational failures. After all, the built-in power electronics is the central element of wind turbines that enables a smooth operation.