Three-phase unbalanced voltage sag detection method based on morphological filtering

Abstract

In dynamic voltage restorer (DVR), accurate and fast voltage sag detection method is the key. However, in the case of three-phase imbalance, the traditional voltage sag detection method still has shortcomings in real-time and accuracy. Therefore, a voltage sag detection method based on morphological filter is proposed. That is, based on the commonly used dq transformation method, the morphological filter is used to replace the Butterworth low-pass filter to suppress the second harmonic generated by the negative sequence component after dq transformation in the case of three-phase imbalance, reduce the system delay and improve the real-time and accuracy of the detection method. The morphological filter is designed, and the appropriate structural elements and morphological transformation algorithm are selected. The results show that the morphological filter has good filtering effect and small delay, and can better meet the detection requirements of DVR.