Hybrid Feedforward Single-Phase Phase-Locked Loop for Accurate Measurement Offset Rejection and Frequency–Ramp Tracking

DC offset (DCO) in the input signal causes estimation inac-curacy in the phase-locked loop (PLL) output. This letter provides a solution to DCO rejection while simultaneously offering frequency–ramp tracking capability to a single-phase PLL, which is an integral part of the renewable energy-interfaced grid-connected converter control system. This has been achieved by using a frequency-fixed DCO rejection method in the preloop stage. Moreover, to accurately track the frequency–ramp without sacrificing dynamic performance, a quasi-type-2 loop filter is used inside the PLL. Unlike conventional single-phase counterparts, the proposed method can reject DCO without interacting with the PLL loop and offers easy implementation and gain tuning, simplifying the overall control system design for the converter control system. Comprehensive quantitative and qualitative results are provided to demonstrate the suitability of the proposed method over the existing literature. Compared with conventional counterparts, the proposed technique achieved at least a 26% reduction in harmonics and had the lowest peak overshoot with the fastest settling time.