A new PLL structure for single-phase grid-connected systems

The phase angle is a critical parameter for the operation of grid-connected systems. The limited amount of information available for the single-phase systems for the phase angle detection requires phase-locked-loop (PLL) methods more advanced than those used three-phase systems. The main difference between the methods is the orthogonal system generator (OSG). This paper presents a phase-locked-loop method for single-phase systems based on a new orthogonal system generator. The proposed structure uses a single high-order integrator to generate the orthogonal voltage system. The method has a simple discrete implementation, filters the harmonic components and eliminates the dc-offset of the sampled grid voltage without delay by the same structure. The operation of the PLL under distorted utility grid conditions is presented. Simulation and experimental results validate the theoretical approach.