Direct Power Control of DFIG System Without Phase-Locked Loop Under Unbalanced and Harmonically Distorted Voltage

Abstract

This paper proposes an improved direct power control (DPC) strategy for the rotor-side converter (RSC) and grid-side converter (GSC) of the doubly fed induction generator under unbalanced and distorted voltage conditions. The proposed scheme is implemented in a synchronous reference frame with the fixed angular speed, so that the phase-locked loop can be removed and relevant potential instability issues can be avoided. Besides, the sequential separations and complex calculations of the power compensating items can be eliminated with the direct-resonant method based on a dual-frequency frequency adaptive vector PI. Thus, the negative and harmonic components can be directly eliminated, achieving balanced and sinusoidal current injected into the power grid. Meanwhile, the control strategy can achieve self-adaptive to the grid frequency variation in the practical situation with the proposed frequency estimation scheme. Finally, the experimental results validate the availability of the proposed DPC strategy.