A New Method for DFIG Control under Unbalanced Grid Voltage Conditions

This research presents a comprehensive analysis of the performance of direct power control (DPC) for doubly-fed induction generator (DFIG) under both balanced and unbalanced network voltages. Voltage unbalance in three-phase systems results in the presence of positive and negative sequences in both voltages and currents. This unbalance leads to many issues, including active power ripple, reactive power ripple, and an increase in the Total Harmonic Distortion (THD) of the stator current. Therefore, it is crucial to have efficient control of the system to reduce power fluctuations. This research presents two solutions that aim to mitigate the fluctuations in both active and reactive power. The first strategy employs PI regulators within the controller system. A high selectivity filter (HSF) is employed to separate the fundamental component of stator phase currents from the harmonic components. The second option utilizes DPC (Direct Power Control) based on stator flux. The suggested method computes the active and reactive powers that correspond to positive sequence variables. Since grid unbalance has a smaller impact on stator flux compared to stator voltage, it can be demonstrated that the second suggested controller exhibits superior performance to the conventional DPC controller in unbalanced situations. To evaluate the effectiveness of the suggested techniques, a simulation is conducted on a 2MW Doubly-Fed Induction Generator (DFIG) system using the MATLAB/Simulink environment. The results demonstrate that both of the suggested DPC control approaches outperform the conventional DPC controller in terms of control system performance, even under unbalanced situations. Furthermore, these improvements are achieved without significantly increasing the complexity of the control system.