New method for the detection of voltage sag based on Hilbert transform and dq transform

The voltage sag is one of the most serious dynamic power quality problems which influence normal and safe operation of many electric equipments. In order to accurately measure characteristic parameters of voltage sag, we proposed a novel detection method of voltage sag based on Hilbert transform and dq transform. First, the α-β coordinate was structured according to actual measured voltage and its Hilbert transform, and then the α-β static coordinate was transformed into the dq rotating coordinate, and finally the amplitude and phase angle of voltage sag were calculated from dq transform outcome. Compared with 90° delay method, conventional voltage sag detection method, the simulation results verify that the new method is correct and effective. The new method which has short response time overcomes the short disturbance of 90° delay method, and has slightly higher detection accuracy than 90° delay method.