Peak detection method using two-delta operation for single voltage sag

In this paper, the proposed system is presented the detection method of sags/swells when a fault occurs in the grid-voltage. The conventional sag detector is from a single-phase digital phase lock loop (DPLL) based on a d-q transformation using an all-pass filter(APF). The d-q transformation is typically used in the 3-phase coordinate system. As present system using single-phase coordinate system, q-axis doesn´t exist to convert stationary reference frame. To realize this transformation, the All-Pass Filter used to generate virtual q-axis with 90° through the grid voltage. However this method doesn´t immediately recognize when it occurred the sag or momentary power failure that is variable to drop the power-quality in grid voltage. Due to delayed phenomenon, the signal of sag transmits to system late. In this paper, the rapid sag / peak detector is proposed using 2nd component of change of Vgds. To review the validity of proposed system, compare to conventional and proposed method through the simulation and experimental results.