Processing of Symmetrical Components in Time-Domain

A novel system for decomposing a set of three-phase signals into its constituting symmetrical components is proposed. The system also estimates the frequency, the magnitudes and phase-angles of the sequence components. The system is useful for online estimation of instantaneous symmetrical components and their attributes in the presence of frequency variations. The proposed system can be considered as a fundamentally improved version of the conventional three-phase Phase-Locked Loop (PLL) system which is widely used in power system applications. From this viewpoint, the proposed system obviates the inherent shortcoming of the conventional PLL system which is its erroneous response in the presence of negative-sequence component. Mathematical derivations and computer simulations are presented to describe the principles of operation and the performance of the proposed system. Examples of applications of the proposed system are in Flexible ac Transmission Systems (FACTS), HVDC systems, and Custom Power Controllers