This thesis presents an alternative control scheme with a simple structure for control of DFIG under unbalanced grid voltage without decomposing the positive and negative sequences. This control method is established based on a modeling which uses instantaneous real and reactive power instead of components of currents. Therefore, in addition to the simplified control structure, the proposed control approach offers a robust structure as its state variables are independent of qd frame of reference. The sequential loop closing technique is adopted to design a multivariable control system under balanced grid voltage. Furthermore, the control system is adopted for improving the performance of the DFIG under unbalanced grid voltage and improving the stator voltage of generator. The main features of the proposed control system compared to unbalanced vector control and DPC methods are simplicity of realization and fast dynamic response because the power components are directly controlled without involving the reference current calculation and carefully tuned current control loops and no synchronous coordinate transformations and sequential decomposition of currents are required. Key Words Wind turbine generator, doubly fed induction generator (DFIG), unbalanced grid voltage, instantaneous power, power limiter.
