A Modified SOGI-FLL with DC-Offset Rejection Feature for Grid-Connected Single-Phase PV Inverter in Shipboard Power System

By increasing the use of different power electronic devices in the propulsion system and other applications in ships, the shipboard grid voltage may face issues, including dc-offset voltage, variations in voltage, and frequency. When a photovoltaic (PV) generation is utilized in a ship to provide auxiliary or emergency power to inject the current into the grid, 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 paper, a phase-lock loop (PLL) algorithm based on a new frequency-lock loop (FLL) structure is proposed. The proposed 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 is not dependent on the frequency. Moreover, the proposed PLL algorithm doesn’t have the drawback of the input DC offset due to using DC offset rejection loop. The proposed approach has been simulated in MATLAB/Simulink environment. The simulation results for variations in voltage frequency, amplitude, and phase have been presented in the paper to confirm the validity of the proposed method.