Small-Signal Stability Analysis of Three-Phase Four-Wire System Integrated With Single-Phase PV Inverters Considering Phase to Phase Coupling Effect Under Asymmetric Grid

With the rapid growth of renewable energy sources, single-phase rooftop photovoltaic inverters connected to the distribution network have received widespread applications in recent years. In such a distribution network, asymmetric fault problems are likely to occur, and small-signal stability during asymmetric faults becomes important. The existing papers analyzed the sequence impedance and related stability issues during asymmetric faults in a three-phase three-wire system. In contrast, the SIs connected to three-phase four-wire systems requires consideration of the effect of zero-sequence components and the phase to phase coupling effect. Because both the zero-sequence component and phase coupling effect will affect the impedance characteristics of the inverter sub-system and thus the stability of the power system. Therefore, this paper established the
$3\ast 3$
admittance model matrix for the inverter sub-system considering the frequency coupling effect and phase coupling effect under asymmetric fault. Based on the admittance model matrix, the main factors including phase-locked loop bandwidth and grid neutral inductance that affects the phase to phase coupling effect are also analyzed. In addition, this paper studies the effect of phase-locked loop bandwidth, short circuit fault degree, and short circuit location on system stability. The validity of theoretical analysis is further verified through the experimental results.