Effect of conventional grid-voltage feedforward on the output impedance of a three-phase photovoltaic inverter

In this paper the small-signal model of a three-phase photovoltaic inverter is upgraded to include the grid-voltage feedforward. The feedforward is shown to increase d and q-components of the inverter output impedance which makes the inverter more insensitive to impedance-based interactions and explains the reported improvement in the output current harmonics. However, using a low-pass filter in the feedforward path is shown to deteoriate the effectiveness of the feedforward already at the frequencies one decade below the cut-off frequency of the low-pass filter. The effect of the feedforward is verified by extracting frequency responses from a switching model and from a prototype inverter operating at reduced voltages.