SAG DETECTION METHOD AND SYSTEM FOR GRID VOLTAGE

摘要

The present invention relates to a sag detection method and a system for grid voltage. The sag detection method for the grid voltage in the present invention comprises: a step (a) for converting grid voltage to the fixed coordinate system of d axis and q axis; a step (b) for primarily converting the d axis and q axis voltage which is converted to the fixed coordinate system based on the difference between a present value and a previous value; a step (c) for secondarily converting the d axis and q axis voltage which is primarily converted based on the difference between the present value and the previous value; a step (d) for calculating a peak value of the secondarily converted part; and a step (e) for judging by comparing X that is the secondarily converted part of the d axis in the step (c) with Y that is the peak value in the step (d). If the X exists within "Y", the grid voltage is in a normal mode. If the X is out of "Y", the grid voltage has sag. According to the present invention, the sag detection method and system accurately and rapidly detect sag, easily detect sag even in a zero-crossing part, and stably perform a changeover in an UPS mode by converting the grid voltage to the fixed coordinate system and detecting sag by converting d-axis voltage and q-axis voltage based on the difference between the present value and the previous value.