Control Strategies for DFIG-based Wind Turbine Systems Contributing to LVRT improvement and Grid Primary Frequency Adjustment

According to the new technical requirements and standards proposed by the grid operator, wind turbine systems (WTSs) based on doubly-fed induction generator (DFIG) must participate in power system management in the case of grid disturbances such as voltage dip and frequency regulation. Moreover, all WTSs must contribute to voltage and frequency support during and after grid failures. In this paper, the implementation of low voltage ride through (LVRT) and inertial response control based on sliding mode controllers (SMC) to avoid the disconnection of WTS from the grid during faults are investigated. The first strategy consists of keeping the stator flux in a required level to ensure the DFIG’s magnetization, and the insertion of the crowbar resistors in the rotor circuits to limit the rotor and stator currents and the DC bus voltage during voltage dip. The second strategy permits to create an artificial inertial response during frequency drop by means of the kinetic energy stored in the WTS’ rotating masses. The aim of this strategy is to contribute in the network frequency stabilization and, therefore, the need for additional power afforded by conventional generators.