Direct power control of a brushless doubly-fed induction generator under an unbalanced power grid

The output power of the brushless doubly-fed generator (BDFIG) in unbalanced power system contains the second-harmonic fluctuation and the stator current is distorted. To reduce the influnce of unbalanced power grid on BDFIG, the composition of instantaneous active and reactive power of BDFIG stator output under unbalanced power grid is deduced and analyzed, and a new approaching rate integral sliding mode variable structure with PI controller is proposed. The integral sliding mode variable structure is used to control the DC component of the output power of BDFIG under the unbalanced power grid. The double frequency fluctuation of power and the distortion of stator current are suppressed by PI control of stator current instruction. Finally, the influence of unbalanced power grid on BDFIG is reduced. In this article, the calculation principle of voltage positive and negative sequence decomposition for unbalanced power grid voltage is studied, and a fast positive and negative sequence decomposition method is designed to improve the delay problem of T/4 delay separation method, the BDFIG direct power control capability under unbalanced grid voltage is improved effectively. Finally, Matlab/Simulink simulation results demonstrate the effectiveness of the control strategy.