A Method for Extracting the Fundamental-Frequency Positive-Sequence Voltage Vector Based on Simple Mathematical Transformations. - Helber E. P. de Souza; Fabrício Bradaschia; Francisco A. S. Neves; Marcelo Cabral Cavalcanti; Gustavo Medeiros de Souza Azevedo; Josué P. de Arruda (IEEE Trans. Ind. Electron., 2009)