Fast and accurate acquisition of positive sequence components of unbalanced grid voltage is an essential requirement to ensure the safety operation of the grid-connected inverter. To improve the extraction speed of positive sequence components of unbalanced voltage

this study proposes a sampling period delay filter (SPDF) to quickly separate positive and negative sequence components by delaying two sampling periods of grid voltage in dq frame. With the SPDF method

only one coordinate transformation is required and the computational burden can be reduced apparently. Then

the noise immunity performance of the proposed SPDF algorithm is investigated; and the corresponding solution

operation period delay filter (OPDF)

can guarantee the desired fast response performance under the premise of limiting the amplified noise within the acceptable range. Finally

the feasibility and priority of the above two algorithms have been verified by the simulation and experimental results.