Stability Evaluation of DC Distribution Systems With Multiple Voltage Source Converters and Multiple DC Transformers

A DC distribution network (DCDN) consists of DC transformers (DCTs), voltage source converters (VSCs), along with multiple long power cables. In such systems, the DC bus voltage may exhibit oscillatory behaviour due to the mismatch between the cable impedance and port impedances of DCTs and VSCs. In this paper, the cascaded stability of a typical dual-terminal DCDN considering the terminal impedance models of VSC and DCT is investigated. The effect of cable impedance and the number of VSCs and DCTs on the DCDN bus voltage stability are evaluated. Furthermore, an active damping method of DCTs proposed in the previous work is analyzed as an example to reveal that the cascaded stability of DCDN can be enhanced if an active damping controller is implemented for DCTs. The works in this paper provide a theoretical basis for optimizing the design and stable operation of DCDNs.