Limit analysis of RSC control for DFIG based wind turbines with asymmetrical faults
For doubly fed induction generator(DFIG) based wind turbines,the low voltage ride through(LVRT) capabilities of different rotor side converter(RSC) control methods vary depending on the specific RSC control methods.However,there is a limit for RSC control methods due to the limited voltage output of the RSC.The control limit for asymmetrical voltage dips is analyzed using an optimal RSC control method based on optimal control theory to minimize the rotor current.The RSC control limit for asymmetrical faults is obtained and the LVRT capabilities of RSC control methods are evaluated.Finally,a typical 1.5 MW DFIG based wind turbine is used to analyze the limits of RSC control for three types of asymmetrical voltage dips.The results show that for the same voltage dip depth,phase to phase faults are the most difficult to ride through,while single phase to ground faults are the easiest.