ESTIMATION OF SYMMETRICAL COMPONENTS WITH FAST DYNAMICS FOR VSC-HVDC

This work presents an innovative symmetrical components estimation algorithm for three-phase ac systems by transforming the time-domain voltages into the complex variable domain. The symmetrical components estimation is attained without the need of a phase-locked loop (PLL). Moreover, as opposed to the standard PLL approach, the estimation of ac frequency and phase is decoupled in this work. The proposed method outperforms a standard PLL in terms of its open-loop phase step response. Furthermore, the estimated phase angle generated by the proposed method has been used to successfully control a VSC-HVDC scheme during steady-state and transient operating conditions in a computer simulation environment. In summary, the proposed method presents an efficient mechanism to generate a reliable ac phase estimation under fast dynamics of the ac system voltage, with minimal computational effort, for VSC-HVDC converters connected to weak ac grids.