New Enhanced Digital Phase-locked Loop Based on Variable Frequency Average

A new design method of enhanced digital phase-locked loop(EPLL) that used in single-phase grid-connected system was presented.The improved EPLL is based on the principle of variable frequency average(VFA) that eliminates harmonics.The modules of frequency control and initial phase angle position were added in.The model inherits some salient advantages of the existing EPLL,such as fast tracking speed,structural simplicity and high sensitivity.Compared with the existing EPLL,the improved EPLL provides more robustness to harmonics and frequency fluctuation that exist in the signal used as the basis of synchronization.Taking several line disturbances such as phase-angle jump,voltage sag,frequency step,and harmonics content into consideration,the proposed method was simulated in Matlab software.Real time experiments based on a TMS320F2812DSP platform were conducted for the proposed PLL.The simulation and experimental results both verify the feasibility of the method.