Comprehensive small-signal model and stability analysis of VSC-based medium-voltage DC distribution system

DC distribution technology is emerging as a prospective form of future power system owing to its advantages such as high controllability and easy compatibility. In medium- or low-voltage DC distribution systems, the two-level voltage-source converter (VSC) has become one of the preferred topologies for grid-connected converters. A comprehensive small-signal model for VSC-based DC distribution systems, which takes into consideration the AC filter, DC distribution cables, and all the controllers in the VSC is presented in this study. Based on the ideal AC source, an absolutely stable synchronous rotating coordinate system is built to preclude the influence of the short circuit ratio of the AC system. The proposed model is verified using a detailed electromagnetic transient simulation carried out using power systems computer-aided design (PSCAD). To analyse the impact of neglecting the AC filter and phase-locked loop controller, two simplified models are established, and a detailed comparison of the three models is presented. The results indicate that when using the two simplified models, the time-domain responses are significantly different from those in the PSCAD simulation and the obtained feasible domains of the control parameters tend to be either more optimistic or conservative. Thus, to carry out a small-signal stability analysis, the use of the proposed comprehensive model is recommended to ensure the safety of the DC distribution system.