Properties and control of variable speed doubly fed induction generator

The paper presents properties and control methods of grid-connected doubly-fed induction generator (DFIG). The paper is focused on unbalanced grid operation, because presently it is the biggest challenge for this type of generator. There are discussed three most popular methods - direct power control, direct torque control, and vector control with proportional-resonant PR controllers of rotor current in stationary alpha-beta frame. In each method, the reference signals of electromagnetic torque, instantaneous power components and rotor current components are calculated without sequence decomposition.