Improving Single-Phase Inverse Park Transform PLL Performance Under Harmonic Distortions

Harmonic distortions in grid voltage pose significant challenges to the performance of single-phase phase-locked loops (PLLs), particularly affecting the accuracy of frequency and amplitude estimation. This paper presents an enhanced design of the Inverse Park Transform PLL (IPT-PLL) incorporating three types of harmonic filtering techniques: band-pass, notch, and finite impulse response (FIR) filters. Each filter is applied at different stages of the system to mitigate harmonic effects while preserving dynamic performance. Theoretical analysis demonstrates how grid voltage harmonics propagate into the synchronous reference frame voltages, resulting in ripple in the estimation signals. Simulation and experimental validations compare the performance of the traditional IPT-PLL with versions incorporating each filtering method. The results confirm that the proposed filtering strategies significantly enhance the estimation accuracy of the IPT-PLL under distorted grid conditions.