Abstract: With the continuous growth in the installed capacity of new energy, the stable operation of the power system has been greatly challenged. The key for the new energy system to actively supporting the stable operation of the power grid is to quickly and accurately detect the sequence components of the power system under the unbalance condition. Accordingly, this paper mathematically deduces an open-loop detection method for sequence components based on the orthogonal signal and delayed sampling period. First, the orthogonal signal construction method is used to construct the orthogonal signal of the grid voltage in the dq frame. Subsequently, the delayed sampling signal, the grid voltage and its orthogonal signal are used to extract the sequence components quickly and accurately using the mathematical operation rules. Secondly, in order to eliminate the fluctuation caused by the detection method in the dynamic response time, this paper proposes a calculation error avoidance method, which avoids the calculation error by judging the real-time state of the grid voltage signal. When the grid voltage is unbalanced, this method can quickly and accurately extract the amplitude and phase of the positive and negative sequence components, and the dynamic response time is less than 3ms. Finally, the results of the simulation experiments prove the correctness and practicability of the proposed method. The fast response, high precision and easy implementation of this method provide a guarantee for the new energy system to actively support the power grid.