Unbalanced Voltage Compensation Strategy for Doubly Fed Induction Generator Based on Self-Synchronization Control without Phase-Locked Loop

This paper investigates the unbalanced voltage compensation strategy of the point of common coupling (PCC) for doubly fed induction generator (DFIG) based on self-synchronization control without phase-locked-loop (PLL). The direct power control (DPC) scheme is implemented in a synchronous reference frame with the fixed angular frequency to avoid potential instability issues caused by PLL under nonideal grid voltage. The unbalanced voltage compensation strategy is proposed based on resonant compensator of PCC voltage. In order to balance the operation performance of DFIG and the power quality of PCC voltage, this paper uses a hybrid virtual impedance (HVI) method to achieve flexible compensation and avoid overmodulation, which needs both the feedforward of the PCC voltage and the feedback of the output current to develop the voltage references. Finally, the results of simulation validate the availability of the proposed compensation strategy.