Control of doubly-fed induction generators under asymmetrical grid conditions

In the presented study a control scheme for the control of doubly-fed induction generators (DFIG) in wind power plants during slight and long lasting asymmetries is developed. The proposed strategy is based on the field-oriented control. The machine side as well as the grid side control are considered. Additional controllers are deployed for the negative sequence currents. This allows achieving additional control targets during asymmetrical grid voltages, e.g. the reduction of electrical torque oscillations. The suggested control scheme was tested by simulations using the program PSCAD^TM/EMTDC. Some simulation results are given to show the potential performance improvement of the DFIG-control-system with the proposed control strategy.