A New Three-Phase DPLL Frequency Estimator Based on Nonlinear Weighted Mean for Power System Disturbances

A new three-phase digital phase-locked loop (DPLL) is proposed to determine the instantaneous grid frequency under power system disturbances. The proposed solution is based on single-phase DPLL algorithms, defining the estimated grid frequency as a nonlinear weighted mean of the three single-phase DPLL outputs. Orthogonal signals required by the DPLL algorithms are obtained through a fictitious quadrature voltage using five different appropriated approaches. The proposed structures have been assessed through extensive analysis under balanced and unbalanced conditions. For this purpose, real voltage dips collected in a Spanish wind farm along several months are included in the paper as examples of frequency estimations. In addition, results from conventional three-phase DPLL topologies are presented to confirm the validity of the proposed DPLL structures.