Improved Feedforward to Enhance Harmonic Suppression for Grid-Connected Inverter

In most cases, for grid-connected inverters, the grid is not ideal at the point of common coupling. When proportional feedforward is used to suppress grid voltage harmonics, the existence of grid impedance will deteriorate the stability of grid-connected LCL-filtered inverter. To enhance stability, the multi-resonant feed-forward strategy was proposed in some papers. However, because of the phase lag caused by digital delay, the suppression ability of this method to grid harmonics is not good enough. Therefore, this paper proposes a compensation strategy for phase lag of feedforward channel at resonant frequencies, which makes different resonant frequencies correspond to different dq rotation coordinates, and respectively changes initial phase of every dq rotation coordinate properly to compensate phase lag. Then the ability to suppress grid harmonics is obviously enhanced. Finally, experimental results verify the effectiveness of proposed control strategy.