Analysis of Stable Operation Domain for the Multi-Terminal Low Voltage DC System Considering PLL Nonlinearity Dynamics

The multi-terminal low-voltage direct current (MT-LVDC) system realizes the large-scale access of DC source and loads, and improves the flexibility and reliability of the distributed system. However, due to its nonlinear controlled source characteristics of the multi-terminal converter interface and a common DC bus interconnection, a complex instability issue will happen when scheduling the power flow of the whole system. In this paper, the dynamic equivalent circuit of the MT-LVDC system is firstly investigated and built, and considering the dominated nonlinearity dynamics of PLL, the power transmission limitation of each converter is derived. Combined with the power constraints between each terminal, the stable operation domain of the MT-LVDC system is established. Finally, a simulation model in Matlab/Simulink is built to verify the validity of the analytical results.