Positive and negative sequence estimation for unbalanced voltage dips

This paper proposes the use of a complex Kalman filter for the estimation of positive and negative sequences from three phase voltages. A complex voltage is obtained by applying the αβ-transform followed by the dq-transform using a rotational operator. The algorithm for three phase voltages containing K harmonics is also given. In the conventional method, estimation of positive and negative sequences is performed through two steps: the magnitude and phase-angle in each individual phase of the voltages are first estimated and the symmetrical component transformation is then applied. The proposed method offers a direct estimation of the positive and negative sequences that may reduce the estimation errors. In addition, the proposed method has a reduced computational cost since the number of state variables is reduced to 2/3 as compared to that in the conventional method. An experiment was performed on measured three phase voltage data. Results have shown that the proposed method offers a good estimation.