Advanced control techniques for doubly fed induction generator-based wind turbine converters to improve low voltage ride-through during system imbalances

A doubly-fed induction generator (DFIG) applied to wind power generation is under study for low voltage ride-through application during system disturbances. Conventional dq axis current control using voltage source converters for both the grid side and the rotor side of the DFIG are analyzed and simulated. DFIG operation is investigated under balanced and unbalanced system disturbances. A conventional d-axis and q-axis control applied to a voltage source converter (VSC) during a system imbalance exhibits oscillations in the stiff DC link voltage as well as in the real and reactive powers of the converter. Multiple advanced control methods are explored and compared for imbalance operations. An advanced control technique utilizing both positive and negative sequence domain is evaluated. The approach demonstrates the stabilization of the DC link voltage to a greater extent during a disturbance but is more sluggish than the conventional control. An innovative control strategy that employs the technique of direct power control (DPC) is also investigated. This control achieves real and reactive power stability with simple active and reactive power control variables replacing the current control loops in the conventional case. A modified DPC algorithm is proposed to eliminate the current harmonics created by DPC during system disturbances. The DPC is further extended to the rotor-side converter of the DFIG thus controlling the complete system using this technique. The DPC is implemented using a three-phase converter designed on a PCB using EagleRTM. A Texas Instruments RTM TMS320F2812 DSP is used to implement the control algorithm. The converter is tested for ride through capability using an industrial power corruptor. The results are compared to the simulation results for compliance with standard grid codes.