The NextWIND project aimed to embed advanced system services (SDL) into wind turbine inverters to lower life‑cycle costs by 30 % over a 20‑year horizon. This was to be achieved by raising the inverter system voltage from 690 V to 950 V or by switching from a conventional 2‑level to a 3‑level topology, thereby improving efficiency and enabling new grid support functions. The demonstrator built for the project consisted of two 1 MW back‑to‑back subsystems that could operate in island mode or in grid‑connected mode without additional hardware, and it was used to validate the performance of newly developed power‑semiconductor modules and control strategies.
Key technical outcomes include the design of an inverter capable of delivering a short‑circuit current three times the rated value, providing synthetic inertia, and enabling black‑start capability with regenerative energy sources. The project defined a start‑up constant of 10 s and a maximum frequency gradient of 2 Hz s⁻¹ for the provision of momentary reserve, values derived from typical synchronous generator characteristics and ENTSO‑E guidelines. For short‑circuit current provision, the conventional K‑factor method was extended so that inverters could supply over‑current beyond the rated current before limiting. Two hardware paths were evaluated: a 2‑level topology using 2.3 kV semiconductors, still under development, and a 3‑level topology using 1.2 kV devices, which offers lower risk and higher overall efficiency. Both options were assessed against expected performance and cost data to secure a flexible, economically viable solution.
The project’s six work packages covered requirement definition, research on optimized components, system and component development, control strategy design, demonstrator construction, and system evaluation. The FREQCON GmbH partner focused on work packages three to six, while SEMIKRON Elektronik GmbH & Co. KG coordinated the overall effort and handled research on essential power‑electronics components at chip, module, and driver levels. The Technical University of Dresden contributed by integrating system services into the new inverter architecture and ensuring high efficiency. Regular bi‑weekly remote meetings facilitated knowledge exchange and alignment across the consortium. The project faced delays due to the COVID‑19 pandemic and supply‑chain constraints, leading to a cost‑neutral extension until 31 July 2024.
Funding was provided by the German Federal Ministry of Economic Affairs and Energy under the “Innovations for the Energy Transition” program, specifically the wind‑energy subcategory. The FREQCON part of the project received 440 605 € in grant money. The consortium comprised three partners, each bringing complementary expertise: SEMIKRON as project coordinator, FREQCON as the developer of the hybrid inverter, and TU Dresden as the academic partner focusing on system‑service integration. The project concluded on 31 July 2024, having produced a demonstrator that validates the feasibility of high‑voltage, multi‑level inverters with integrated system services, and establishing a foundation for future deployment of wind‑turbine inverters that can support grid stability while reducing overall costs.