Torque Preservation in DFIG Systems During Voltage Dips With Modulated Stator-Connected Dynamic Braking Resistor

This paper proposes a novel approach to enhancing the low-voltage ride-through (LVRT) capability of doubly-fed induction generator (DFIG) wind turbines using a dynamically modulated braking resistor (DBR) connected in series with the stator windings. Unlike conventional DBR-based methods that focus primarily on mitigating electrical transients, the proposed approach emphasizes maintaining the generator's electromagnetic torque at its pre-fault level during grid voltage dips. The DBR resistance is calculated in real time based on analytical expressions derived from the system's model. By properly selecting the DBR resistance during the fault, the excess mechanical power that cannot be transferred to the grid is dissipated within the resistor, allowing the generator torque to remain constant during the fault, which helps maintain rotor speed and mitigate electrical transients. The proposed strategy is validated through both simulation and experimental results under symmetrical fault conditions, demonstrating superior torque stability, reduced current transients, and improved post-fault recovery compared to fixed-resistance DBR schemes.