An Admittance Modeling Method of Grid-Tied Converter in αβ-Frame Under Voltage Sag

With the development of renewable energies and direct current (dc) loads, the grid-tied converter (GTC) is interface equipment to the power grid, connected to a constant power source (CPS) or constant power load (CPL); however, the oscillation phenomenon of GTC with CPS or CPL shows uncertainty during voltage sag, focusing on the influence of voltage amplitude rather than voltage angle. An alpha beta -frame admittance modeling method for GTC is, thus, proposed to achieve a more accurate analysis during voltage sag, considering the instantaneous synchronous angle and amplitude at the operation point. The proposed modeling process, moreover, retains the control loop in dq frame and translates the admittance in dq frame into that in the alpha beta -frame via inversed Park's transformation; thus, based on the proposed alpha beta -frame admittance model, the influence of both amplitude and instantaneous synchronous angle of operation point on GTC is analyzed comprehensively, determining the responded oscillation of system more accurately during voltage sag. The fuzzy area of the GTC with CPS and CPL during voltage sag is discussed and devised exactly based on the influence of the instantaneous synchronous angle of the operation point. Finally, voltage sag experimental results are presented to validate the correctness of the proposed modeling method.