An Observer Based Phase-Locked Loop with DC-Offset Rejection Capability for Single-Phase Grid-Tied Converter

The presence of a DC offset in the measured grid voltage poses a challenge to the proper synchronization and control of single-phase grid-connected converters. It leads to oscillations and offset errors in the estimated grid voltage parameters. The fast and accurate extraction of synchronizing signals is most important for the high performance of gridconnected systems and for monitoring the grid conditions. To enhance the performance under DC-offset input grid voltage condition, this paper presents a quadrature signal generation (QSG) approach based on an observer (OB-QSG). Utilizing the OB-QSG, a phase-locked loop (PLL) is realized. The results are compared with an advanced SOGI-based PLL under various grid disturbances, along with the DC offset. The mathematical modeling of the OBQSG is also presented.