Single-line-ground fault, which happens at the delta terminal of a Yg∆ transformer or the ungrounded wye terminal of a YgY transformer in a grid-forming inverter system will cause severe overcurrent and overvoltage simultaneously. However, they are rarely investigated together and mitigated through a control strategy at the same time. In this paper, phase voltages and inverter output currents during the fault are firstly calculated based on the sequence network of the system. Subsequently, to ride through the faults, the hybrid mitigation strategy based on the virtual negative-sequence and positive-sequence impedance is proposed.
