A novel fast detection algorithm for grid symmetrical components extraction

One of the important issues in the operation of three phase grid-connected converters is fast and precise detection of fundamental frequency positive and negative sequence components present in three phase input voltages. A new detection algorithm based on complex least squares is proposed. This algorithm can detect amplitude and phase of grid voltage positive and negative sequence accurately and rapidly when the voltage contains high order harmonics and random noise. Because of the assumption that the frequency is known, the algorithm can´t track grid frequency variation. Kalman filter has many similarities with least squares, and it contains state equation and output equation which can estimate more grid information. Based on the above ideas, this paper proposes an improved algorithm which not only separates positive and negative sequence components, but also detects frequency variation. The simulation results verify the correctness and validity of the algorithm.