Analysis of the control limit of crowbar-less LVRT methods for DFIG-based wind power systems under asymmetrical voltage dips

For doubly-fed induction generator (DFIG)-based wind power systems, when crowbar-less control methods are used for low voltage ride through (LVRT), the LVRT capabilities are different depending on the specific method. However, because of the limited voltage output of rotor side converter (RSC), there is a limit for crowbar-less control methods. In order to analyze the limit under asymmetrical voltage dips, an optimal crowbar-less control method is proposed to minimize the rotor current during faults. Based on the proposed method, the control limit under asymmetrical faults can be obtained, and then the LVRT capabilities for asymmetrical faults, with crowbar-less control methods, can be evaluated. Finally, a case study of a typical 1.5 MW DFIG-based wind power system is carried out, and from the results, it can be seen that among the three types of asymmetrical faults, the phase-to-phase faults are the most difficult to ride through, and the single-phase-to-ground faults are the easiest to ride through.