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A novel scheme for obtaining the fundamental-frequency positive-sequence grid voltage vector based on a generalization of the delayed signal cancellation method is proposed in this paper. The technique is implemented by sampling and storing the instantaneous αβ voltage vector. A mathematical transformation is then proposed through which the current and delayed voltage vectors are combined. It is shown that the proposed transformation has unity gain for the fundamental-frequency positive-sequence voltage vector, while its gain is equal to zero for some chosen components. Cascaded transformations can then be used for eliminating the fundamental-frequency negative-sequence vector, as well as chosen positive- and negative-sequence harmonic vector components and, thus, for accurately obtaining the fundamental-frequency positive-sequence voltage vector. The output of the last transformation block is input to a synchronous reference frame phase-locked loop for detecting frequency and position of the positive-sequence vector. A proposal for making the scheme frequency adaptive is also presented. The good performance of the proposed method is verified with simulations and experiments by using distorted and unbalanced signals, containing fundamental-frequency as well as positive- and negative-sequence harmonic components. The proposed method frequency adaptation capability is also verified.
Date of Publication: July 2010