Three-phase dynamic voltage restorer with a robust voltage sag detection method

In this paper, a new sag detection algorithm for a dynamic voltage restorer (DVR) is proposed. The proposed detection algorithm has a hybrid structure composed of an instantaneous value comparison part and a peak variation calculation part. The peak variation calculation part calculates the fundamental and harmonic components by using the discrete Fourier transform, and has a constant detection response regardless of phase angle at which sag occurs. The instantaneous value comparison part compares a measured voltage value with a reference value, which is compounded by the harmonic components obtained from the peak variation calculation part. Therefore, the proposed detection method shows a fast and robust response even under the distorted grid voltage condition, which is polluted by harmonics. The proposed method is verified by simulation and experiment with 10kVA DVR prototype.