An Efficient Hybrid Filter-Based Phase-Locked Loop under Adverse Grid Conditions

Abstract

Synchronous-reference-frame phase-locked loop (SRF-PLL) is widely used in grid synchronization applications. However, under unbalanced, distorted and DC offset mixed grid conditions, its performance tends to worsen. In order to improve the filtering capability of SRF-PLL, a modified three-order generalized integrator (MTOGI) with DC offset rejection capability based on conventional three order generalized integrator (TOGI) and an enhanced delayed signal cancellation (EDSC) are proposed, then dual modified TOGI (DMTOGI) filtering stage is designed and incorporated into the SRF-PLL control loop with EDSC to form a new hybrid filter-based PLL. The proposed PLL can reject the fundamental frequency negative sequence (FFNS) component, DC offset component, and the rest of harmonic components in SRF-PLL input three-phase voltages at the same time with a simple complexity. The proposed PLL in this paper has a faster transient response due to the EDSC reducing the number of DSC operators. A small-signal model of the proposed PLL is derived. The stability is analyzed and parameter design guidelines are given. Experimental results are included to validate the effectiveness and robustness of the proposed PLL.