Design and Analysis of a Photovoltaic Power Conditioning System Using Grid Voltage Feedforward Procedure in Weak Grid Condition

The voltage feedforward procedures at the point of common coupling (PCC) are utilized to remove current harmonics caused by grid voltage distortion in the grid-connected inverters. However, due to the time delay effect at the weak grid, the voltage feedforward at the point of common coupling can lead to instability of the grid-connected inverter. In this paper, an improved voltage feedforward procedure is presented to interconnect a photovoltaic power conditioning system to the weak grid. The stability of this system is investigated by impedance-based stability criterion in the presence of the voltage feedforward. Based on this analysis, it is suggested that the feedforward signal should be taken from the grid voltage instead of the PCC voltage. A method is introduced to extract the grid voltage from the measured PCC voltage to solve the challenge of direct detection of the grid voltage. To investigate the effectiveness of the proposed method, the photovoltaic power conditioning system based on the L filter connected to a single-phase weak grid has been simulated in Simulink MATLAB. The simulation results reveal the proper and better performance of the proposed grid voltage feedforward in attenuating the harmonics of the injected grid current, and the photovoltaic power conditioning system maintains its suitable stability in the weak grid condition.

Keywords:

Grid-tied Photovoltaic System , feedforward of PCC voltage , feedforward of grid voltage , digital control delay , Weak grid