Voltage Support Strategy for Improving Power Transfer Capability of Grid-Connected Converter Under Unbalanced Conditions

Grid-connected converter should transmit power from distributed generation to the grid as much as possible, even under unbalanced conditions. However, under the necessary constraints of the point of common coupling (PCC) voltage support and current limitation, it is difficult for the converter to transmit more power to the grid. To fill this gap, this article provides a mechanism analysis of the power transfer considering the zero-sequence voltage influence. Moreover, a new control strategy is proposed to improve the power transfer capability under unbalanced conditions. It is found that the phase difference between the PCC voltage and the grid voltage in the positive- and negative-sequence network is a key factor affecting power transfer capability, while playing an important role in the accurate calculation of the PCC voltage amplitude. Based on the key factor, we propose a new control strategy to improve the power transfer capability of the grid-connected converter. The proposed strategy can flexibly control the phase difference and transfer more power to the grid under the premise of current limiting and voltage support. Finally, the proposed voltage support strategy is validated with an experimental study.