An adaptive phase-locked loop algorithm for single-phase utility connected system

This paper proposes a novel algorithm employed to detect both the phase-angle and the frequency of the single-phase utility grid voltage. The proposed algorithm uses an adaptive notch filter (ANF) operating in conjunction with a Phase-Locked Loop (PLL) system, yielding an algorithm called ANF-αβ-pPLL. The αβ-pPLL structure is based on the instantaneous active power theory for three-phase power systems. Thus, for single-phase systems, the proposed PLL algorithm can be analyzed into a fictitious two-phase stationary reference frame (αβ-coordinates), in which a normalized fictitious quadrature voltage (νβ) is obtained from the estimated PLL phase-angle. On the other hand, an adaptive filter is used to extract the fundamental component of the utility voltage, allowing the rejection of voltage harmonic disturbance. In order to validate the theoretical development, the performance of the single-phase ANF-αβ-pPLL algorithm is evaluated by means of both simulation and experimental tests under utility grid disturbances, such as voltage harmonics, voltage sags/swells, phase-angle jumps and frequency variations.