Implementation of enhanced non-adaptive cascaded DSC-PLLs for renewable energy systems

In recent years, to fast and accurately extract the grid voltage information, using cascaded delayed signal cancellation (CDSC) operators in the prefiltering stage of phase locked loops (PLLs) has become highly popular. Non-adaptive CDSC (NCDSC) operators do not cause the stability problems unlike adaptive CDSC operators. So, researchers use the NCDSC operators intensely. Nonetheless, the NCDSC operators have two main drawbacks: (1) the dynamic responses of NCDSC-PLLs are not fast enough, similar to adaptive CDSC operators-based PLLs; and (2) the imbalance rejection capability of the NCDSC-PLLs dramatically deteriorates in case of large frequency variations. In this paper, to overcome these problems, two enhanced NCDSC-PLLs, which are called the ENCDSC-PLL1, and ENCDSC-PLL2, are suggested. The parameter design procedures of suggested PLLs are given by means of their small- signal models. Since the proposed ENCDSC-PLLs are the nonminimum-phase systems, their stability analyses are evaluated by Nyquist diagram. The feasibility and effectiveness of the proposed ENCDSC-PLLs are validated by experimental results.