New research demonstrates that Nonlinear Auto Disturbance Rejection Control (NADRC) offers a robust solution for mitigating significant torque and active power oscillations in Doubly-Fed Induction Generator (DFIG)-based wind turbines operating under grid voltage imbalance conditions. This advanced control strategy, detailed in recent studies, directly addresses a persistent challenge for DFIGs, which are highly susceptible to grid disturbances, often leading to reduced power quality and potential grid code violations, particularly in weak or isolated grid segments.

DFIGs, widely deployed due to their variable speed operation and partial scale converter requirements, exhibit inherent sensitivity to voltage sags and swells, as well as unbalanced grid conditions. These disturbances induce undesirable oscillations in electromagnetic torque and active/reactive power, impacting the mechanical integrity of the turbine drivetrain and compromising the quality of power injected into the grid. Traditional control methods often struggle to effectively suppress these oscillations without compromising dynamic performance or requiring complex compensation strategies.

The proposed NADRC strategy leverages its ability to estimate and actively compensate for both internal and external disturbances, including those arising from grid voltage imbalances. Unlike conventional Proportional-Integral (PI) controllers, NADRC does not require precise knowledge of the system model, offering superior robustness and disturbance rejection capabilities. Simulations and experimental validations have shown that NADRC can significantly reduce the amplitude of active power oscillations by up to 70% and torque oscillations by 60% compared to conventional control schemes under similar imbalance conditions. This performance enhancement is achieved by effectively decoupling the positive and negative sequence components of the stator voltage and current, allowing for more precise control over the DFIG's output.

This improved control performance translates directly into enhanced grid integration capabilities for DFIG wind farms. By maintaining stable power output and minimizing torque pulsations, NADRC helps DFIGs meet increasingly stringent grid code requirements for fault ride-through and power quality. This is particularly critical as grid operators demand higher levels of ancillary services and reliability from renewable energy sources. The reduction in mechanical stress on the turbine's gearbox and shaft also promises to extend the operational lifespan of these critical components, potentially lowering maintenance costs and improving overall plant availability.

The successful implementation of NADRC represents a significant step forward in enhancing the resilience and operational efficiency of DFIG-based wind energy systems. It underscores the ongoing innovation in power electronics and control theory essential for the stable and reliable integration of large-scale renewable generation into modern electricity grids.