An Improved Real-Time Voltage Sag Detection Method Based on the Short-Time Delay Method

Voltage sag is one of the most serious power quality problems, the detection speed, and accuracy as well as the computational efforts are the essential parts in voltage sag compensation. This paper presents a single-phase voltage sag detection algorithm based on the short-time delay method. The virtual orthogonal voltage signal is constructed based on the single-phase voltage, and then the virtual three-phase voltage amplitude is estimated via the virtual orthogonal voltage signal. Compared with the 90° delay method, the short-time delay method requires fewer sampling points and shortens the detection delay. Compared with the derivation method, the short-time delay method can virtually construct more reliable orthogonal signals and thus a much simpler low pass filter is required in the dq axis, reducing the detection delay time. Simulation and experimental verifications were also carried out to compare the detection accuracy, detection speed, and computational efforts of different detection methods including the traditional dq method, RMS method, FFT method, derivation method, 90° delay method, and short-time delay method. The hardware-in-the-loop test results proved the effectiveness of the presented short-time delay method.