Zero-Mode Current Distribution Analysis in Neutral Ungrounded Distribution Systems with Distributed Photovoltaic Generators under SPG Faults

The fault current is determined by the zero-sequence parameters in neural ungrounded distribution systems (NUDSs) when a single phase-to-ground (SPG) fault occurred. Hence most traditional fault location methods are proposed and realized based on the zero-mode currents along the faulty distribution line. Nowadays, high penetration of distribution generators (DGs) exists in NUDGs and the zero-mode currents would be influenced by these grid-connected inverters. In this paper, the zero-mode currents located at the upstream side and the downstream side of the fault point are analyzed and compared in NUDSs with distributed photovoltaic generators under SPG faults. The equivalent composite sequence network diagram of NUDSs with SPG faults are constructed, and the control strategy of grid-connected inverter is analyzed. The derived zero-mode currents during SPG faults would be verified in the simulation both in the time domain and frequency domain. The results show that the high-frequency components of zero-mode currents are different at upstream side and downstream side of the fault point, while the high-frequency components of zero-mode currents are the same at the same side of the fault point.