Currently

a grid-connected inverter is required to inject a dual-sequence current during asymmetric grid sags

which means both positive and negative sequence phases should be tracked. This paper proposes an open-loop phase synchronization (OLS) method of positive and negative sequences for an asymmetric grid based on the moving average filter (MAF)

which does not need to separate the positive and negative sequence fundamental components of grid voltage. As a benefit

there is no double-frequency oscillation in the estimated phases at off-nominal frequencies since the positive and negative sequence phases are obtained simultaneously. The proposed method not only has the inherent advantages of OLS

but also further improves the dynamic response since the window length of MAF is only 1/6 of the fundamental period. The effectiveness of the proposed OLS is verified by experimental results.