Analysis of discrete VS-PLL structure used for grid parameters estimation

Phase-locked loops (PLLs) are doubtless the most popular synchronization technique in the power converters. Almost all proposed PLL structures known in literature are inherently nonlinear and can be linearized as second order linear time invariant system. Nonlinear nature of PLLs degrades their performances, and question arises if there exist an enhanced PLL structure that would have superior performances. In this paper we propose an three-phase nonlinear PLL structure based on sliding mode control theory and it is named variable structure PLL (VS-PLL). In order to implement this structure on an digital platform, fixed point mapping is performed and corresponding VHDL code is generated by MATLAB HDL coder. Excellent behaviors of continuous and discrete form VS-PLL structure in steady and transient states are confirmed by simulations.