Abstract
The estimation of phase-angle, frequency, and amplitude are vital for the control of grid-connected power electronic systems in both single-phase and three-phase systems. The single-phase enhanced phase-locked loop (1P-EPLL) and two-phase enhanced phase-locked loop (2P-EPLL) techniques can be used to estimate single-phase and three-phase grid voltage quantities, respectively. However, under the presence of harmonics, unbalance, and dc offsets, the estimated quantities by these enhanced phase-locked loops (EPLLs) may contain periodic ripples. These periodic ripples are eliminated by using multiple delayed signal cancellation (MDSC) filters in the phase-angle estimation loop and amplitude estimation loop of these EPLLs. To improve the dynamic responses of MDSC-based EPLLs, proportional-integral (PI) controller is replaced with a proportional-integral-derivative (PID) controller. The design guidelines for choosing the control parameters are provided. The MDSC filters in the EPLLs are realized both in direct-form and recursive-form structures. The proposed EPLLs are verified experimentally by using real-time system and compared with recent advanced EPLLs.