Fast Symmetrical Component Extraction From Unbalanced Three-Phase Signals Using Non-Nominal dq -Transformation

This letter proposes a new algorithm for the fast extraction of symmetrical components from unbalanced three-phase signals. Being different from the conventional methods for the decomposition of positive and negative sequence components commonly realized at the cost of introducing significant delay, the proposed algorithm assumes the non-nominal dq-transformation to first produce the special d-axis and q-axis components, which will become the pure high-frequency ac signals, and then uses the typical half-cycle delay method to remove the unwanted negative or positive sequence component. Finally, the proper amplitude and phase angle coefficients can be easily calculated to compensate the remaining high-frequency d-axis and q-axis components before transforming them to the expected d-axis and q-axis values of corresponding symmetrical components. The performance of the proposed algorithm is evaluated through simulation and experiment results.