Mechanism Analysis of DFIG-Based Wind Turbine’s Fault Current During LVRT With Equivalent Inductances

Doubly fed induction generator (DFIG)-based wind turbine (WT) has a distinct fault current contribution that is critical for the power system analysis. This article analyzes the mechanism underlying DFIG-based WT's fault current during the low-voltage ride through (LVRT) from the perspective of magnetic circuits. The crowding-out phenomenon is discovered, and the general relationship between flux linkage and current is depicted with the proposed equivalent inductances. Based on the understanding, a new analytical method for deriving the analytical expressions of fault current is proposed. Compared with the existing methods that rely on solving the ordinary differential equations (ODEs), the proposed method is based on the algebraic operation derived from the magnetic circuits, which makes it appropriate for different fault scenarios. Using this method, the stator current is depicted with a series of succinct expressions. The analytical results are verified by experiments and simulations on a 10-kW DFIG prototype. The differences in fault current between the synchronous generator (SG) and DFIG-based WT are identified. This article is expected to help in understanding the regularities of DFIG-based WT's fault current from a physical perspective. The analytical results are expected to be helpful for rating circuit breakers and studying issues related to protective relays.