A new phase-locked loop method for three-phase system

Stability and rapidity of phase angle detection in grid synchronization system is very important, especially when grid voltage is under adverse conditions. This paper presented a fast direct calculation phase-locked loop (FDC-PLL) method which can detect phase angle directly from the corresponding relationship between the absolute value of grid voltage and the phase angle. And the d-q conversion is not needed in FDC-PLL. Moreover, when gird voltage is unbalanced or distorted, the positive-sequence fundamental component (PSFC) of grid voltage is extracted through double second order generalized integrator (DSOGI), and phase angle is calculated by using PSFC. As a consequence, the effectiveness and feasibility of the presented PLL algorithm is verified by simulations and experiments.