Potential and Challenges in LVRT for Grid-Forming Wind Turbines Brought by the Emergence of New Power Modules With Enhanced Short-Circuit Current

Improving the short-circuit current capability of converters can directly enhance the low-voltage ride-through (LVRT) performance of doubly-fed induction generator (DFIG) based wind turbine systems (WTS). Previously, this approach was limited by power semiconductor modules and costs. Recent advances in materials and modulation strategies have greatly boosted their short-term overcurrent capability (up to 3.0 p.u. for 3 s) with only an approximate 3.3 % increase in the total wind turbine cost. This progress makes it necessary to assess the potential and challenges in its practical applications in LVRT for grid-forming wind turbines. First, the grid-forming control strategy for DFIG-based WTS under symmetrical grid faults is presented and the transient model is established. Second, new boundaries of the WTS are quantitatively examined regarding the controllable region, the power support capability, and the transient stability margin. Compared to before, the enhanced power modules enable wind turbines to better support voltage and expand the stable operation area without activating crowbar circuits. Third, issues of dc-link voltage drops and fluctuations when DFIGs operate at subsynchronous speeds during LVRT are studied. Results indicate that reducing the proportional coefficient of the rotor-side converter current loop and switching the grid-side converter to active power priority mode can solve this problem. Finally, theoretical results are verified by real-time simulations and experimental results.