Design and DSP-based validation of a cascaded DSOGI-PLL for mitigating grid disturbances

Abstract

Ensuring a smooth power injection into an electric grid in the presence of imperfections, such as phase disturbances, voltage imbalance, frequency variations, harmonics, and DC offsets, requires fast and robust phase-locked loop (PLL) techniques. Among these, the double second-order generalized integrator (DSOGI)-based PLL is widely used due to its strong performance in challenging grid conditions. However, conventional DSOGI-PLL has limitations in handling DC offsets and harmonic disturbances. To address these challenges, this paper introduces the design of a cascaded DSOGI-PLL that enhances attenuation of DC components and low-order harmonics while maintaining computational simplicity for DSP-based implementation. Experimental validation on a TMS320F28379D DSP platform demonstrates that the proposed scheme achieves synchronization settling within 48 ms even under severely polluted grid conditions, while reducing output unit-vector THD to 0.5% when the input voltage contains 22% THD. These results confirm the cascaded DSOGI-PLL as a significant improvement over conventional PLLs.