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Improved Predictive Direct Power Control of Doubly Fed Induction Generator During Unbalanced Grid Voltage Based on Four Vectors

This paper presents an improved strategy in the field of predictive direct power control (PDPC) of the doubly fed induction generator (DFIG). The proposed strategy applies four voltage vectors in every period in order to have constant switching frequency and low current total harmonic distortion. The appropriate voltage vectors in each period are recognized when estimated duration times of selected active vectors are positive. The suggested technique shows excellent performance during transient and steady-state conditions. The proposed PDPC can easily follow the power references under normal and abnormal voltage conditions even if the power references contain ac terms. Without any additional controller, the proposed technique could obtain smooth stator active and reactive powers or smooth electromagnetic torque, or could inject sinusoidal and balanced currents into the grid when the unbalanced voltage appears in DFIG stator windings. Simulation studies for this technique are carried out for 2-MW DFIG in MATLAB Simulink environment under balanced and unbalanced grid voltage. The results of this technique under unbalanced grid voltage are compared with two other previous PDPC strategies. Comparisons show that the performance of the proposed strategy under unbalanced grid voltage is superior to the two other strategies.