SOGI based grid fault detection for feeding asymmetrical reactive currents to fulfill LVRT requirements

Due to the increasing wind power penetration, grid codes of system operators require low voltage ride through (LVRT) capability for wind turbines (WT). Additionally the WT has to support the power system stability in LVRT cases by supporting the grid with reactive power. The amount of reactive power feed-in depends on the type of grid fault and the depth of the voltage dip. Therefore this paper shows a reliable grid voltage monitoring consisting on a second order generalized integrator (SOGI) structure. The resulting phase locked loop (PLL) is tolerant against grid faults and the amplitudes and phase angles of the individual phase voltages are detected.