An Improved Negative Power Transfer Ability of Battery Grid-Forming Converter under Weak Grid

The grid-forming (GFM) converters have received much attention due to the advantages of voltage and frequency support ability. However, it is also found that the GFM converters would encounter stability problems under a weak grid resulting from the power transfer limit, especially under the negative power transfer case for the battery charging conditions. Thus, this paper investigates the negative power transfer problem of the GFM under a weak grid. It is firstly revealed that the maximum power transfer ability under the charging mode is smaller than the discharging mode due to the resistance effect of grid impedance. Then, the analysis indicates that its maximum negative power can be improved under variable PCC voltage, and a power-based adaptive internal potential feedforward control strategy is proposed. Finally, simulation verification shows the correctness of the mathematical model and the effectiveness of the proposed control strategy.