Simultaneous Voltage and Current Harmonic Control of Grid-forming Converters Based on Unified Harmonic Voltage-Current Droop

As a promising technology, grid-forming (GFM) converters can provide voltage and frequency support in grid- connected mode, and power local loads in islanded mode. Multiple GFM converters connected to the same point of common coupling (PCC) should not only ensure harmonic current sharing, but also reduce the PCC voltage harmonics. Most of the existing solutions need to extract and control each harmonic sequence separately, resulting in enormous calculation. To solve this problem, a harmonic control method for GFM converters based on unified harmonic voltage-current droop is proposed. By establishing a unified droop relation between all harmonic components of PCC voltage and output current, we achieve to share harmonic current according to converter capacity while reducing PCC voltage harmonics. The proposed method is applicable to both grid-connected and islanded modes, and does not need to extract harmonic sequences separately. Compared with existing control methods, it requires less computation, thus easy to be implemented in embedded controllers. Finally, the effectiveness of the proposed control scheme is verified by simulation in the MATLAB environment.