A Robust and Simple Phase-Locked Loop for Unbalanced Power Grid Applications

Abstract

This paper proposes an improved phase-locked loop (PLL) for estimation of frequency and phasors of three-phase voltage and current signals in power systems. It works for balanced and unbalanced inputs amd offers highly robust performance against wide range of input signal attitudes including its amplitude, and angle. Therefore, it can be reliably applied to different signals in power systems such as fault currents and short-circuit voltages. The parameters of the proposed system are conveniently reduced to the selection of two damping ratios based on developing a linear mathematical model. The simulation results confirm that the system is capable of tracking wide range of changes in frequency, amplitude and phase angle with excellent robustness and short transient time. The proposed system not only reduces the computations compared to its counterparts, but also improves a wide range of applications including grid-synchronization of distributed generation units, power quality monitoring, and measurement of synchrophasors.