Grid sequence detector based on a stationary reference frame

This paper proposes a new three-phase positive sequence detector. The structure is based on a stationary reference frame and a Moving Average Filter (MAF) that guarantees the complete cancellation of harmonics and grid imbalances. Performance of the MAF is analyzed mathematically for a proper selection of the window width of the optimal filter in this application. The time delay introduced by MAFs is constant and known; hence, it can be compensated. Furthermore, it completely eliminates any oscillation multiple of the frequency for what it is designed; The proposed detector operates in open loop and there is no PI controller to be tuned. Thus, the dynamic response and simplicity is improved compared to other solutions. Performance of the proposed detector is verified through simulation and experiment. It shows very good performance under extreme grid voltage conditions, allowing fast detection of the grid voltage positive sequence (within one grid voltage cycle).