The Detection Algorithm Based on the Short Time Delay for Three-Phase Unbalanced Voltage Sag

Abstract

To improve the detection speed of the three-phase unbalanced voltage sag, the traditional αβ/dq transformation algorithm can be applied. However, in this algorithm, the virtual quadrature voltage signal (VQVS) needs to be accurately constructed in the αβ coordination system. Then, the information of the voltage jump can be achieved by the αβ/dq transformation. However, the traditional algorithm for constructing the VQVS introduces the harmonic component, so that the detection speed and accuracy is low. To solve the problem, this article modifies the algorithm and presents a new algorithm based on the combination of the short time delay (STD) and the positive- and negative-sequence transformation (PNST) algorithm. The STD algorithm and its construction are firstly detailed. Then, the extraction step and performance of the PNST are given. Since the STD algorithm can avoid harmonic properties, voltage sag signal can be quickly obtained by analyzing the positive and negative sequence component derived from the PNST algorithm. The proposed algorithm is compared with two alternatives already proposed in the literature in terms of detection time. Finally, simulation and experimental results validate the validity of the proposed algorithm.