Analysis of Interactive Behavior and Stability of Low Voltage Multi-terminal DC System Under Droop Control Modes

Low-voltage multi-terminal DC system is one of the important forms in distribution network. Its stability issue has drawn worldwide attention for the characteristics of low inertia and weak damping. This paper aims to analyze the interactive behavior between the voltage source converter (VSC) and the oscillation mode of the DC network. First, this paper proposed a modeling method for DC voltage control loop considering the time-lag effect of inductor energy storage behavior on the AC side of the VSC. Based on this model, the interactive behavior between VSC and DC network including the influence of droop coefficients and load power under DC voltage-AC power (Vdc-Pac) droop control mode and under DC voltage-DC power (Vdc-Pdc) droop control mode is studied. Then, the overall state-space model of the system is established. Furthermore, the stability of a low-voltage three-terminal DC system under different control modes and parameters is compared and detailed analyzed. Finally, the corresponding simulation and experimental verification validate the theoretical analysis. The research results show that under the same capacity and control parameters, Vdc-Pac mode can better improve the capability of power regulation and system stability. This research can provide an effective method for system control modes design.