Reduced sensor operation and power quality improvement in grid-tied doubly fed induction generator using composite and twin frequency generalised integrators

This study presents a strategy involving a reduction in the stator current sensor count for control of power converters, in a doubly fed induction generator (DFIG)-based wind energy conversion system (WECS). The reduced sensor vector control scheme is effectively used in lieu of the conventional vector control algorithm during sensor failure without any change in the overall control structure. This keeps the system operational in case of sensor failure. The reduced sensor scheme necessitates precise estimation of stator flux amplitude and an orientation angle, for control of power converters under all operating conditions. A composite generalised integrator phase-locked loop is presented to estimate accurately the stator flux amplitude and orientation angle, even at operating system irregularities such as unbalanced voltages, lower-order harmonics in the grid voltage, DC bias in sensing circuitry, and so forth, which otherwise lead to distortions in flux and orientation angle. The grid-side converter control is based on a twin frequency improved second-order generalised integrator. It enables fast and accurate power quality improvement in DFIG-based WECS during load and grid abnormalities. A laboratory prototype is developed to validate the control of the system.