A modified SOGI-FLL algorithm with DC-offset rejection improvement for single-phase inverter applications

By the growing penetration of distributed power generation, it is vital to provide power with a satisfying power factor to the grid. Hence, the grid voltage needs to be accurately monitored to synchronize the injected current with the grid voltage. Phase-locked loops (PLLs) are responsible for extracting the phase, frequency, and amplitude of the grid voltage in the control unit of a grid-tied inverter. The proper and fast estimation of grid information under grid disturbances has a significant role in the system's stability. In this study, a modified phase-locked loop (PLL) algorithm based on a new frequency-locked loop (FLL) structure is proposed. The proposed modified PLL algorithm has a high-speed performance in estimating the phase, frequency, and amplitude of the grid voltage. Unlike conventional PLL-based FLLs, the phase shift variation in the proposed algorithm does not affect frequency estimation. Moreover, the proposed modified PLL algorithm doesn't have the drawback of the input DC offset due to the use of the DC offset rejection loop. The proposed PLL structure mitigates the DC offset with a proper speed, and the response speed is enhanced. The control algorithms in this study have been implemented via a creative method. This technique can be applied in cheaper microcontrollers like Arduino Duo so that the monitoring speed is enhanced. Besides, the settling time for the tracking has been enhanced. The proposed approach has been simulated in MATLAB/Simulink environment. The experimental results have also been included to confirm the simulation results and the validity of the proposed method.

Automated summary

A modified PLL algorithm based on a new FLL structure is proposed in this study for high-speed estimation of the phase, frequency, and amplitude of the grid voltage. The proposed PLL structure effectively mitigates input DC offset and enhances response speed. This method contributes to the stability of power systems.