Improved direct power control of doubly-fed induction generator based wind energy system

This paper proposes an improved constant switching frequency direct power control (CSFDPC) strategy for doubly-fed induction generator (DFIG) based wind energy generation systems. Unlike the conventional vector control scheme which is based on rotor current decoupling control, the proposed CSFDPC strategy directly calculates the rotor voltage within each fixed sampling period to reduce the stator active and reactive power errors. Compared to the look-up-table based DPC strategy, constant switching frequency of the rotor side converter is achieved so as to ease the design of the converter and harmonic filter. In order to provide precise stator active and reactive power control and to reduce the steady-state power errors, several compensation strategies are introduced. Simulation results for a 2MW DFIG system are provided to demonstrate the effectiveness and the robustness of the proposed control strategy during variations of active and reactive power and rotor speed.