Control scheme for multi-terminal VSC-based medium-voltage DC distribution networks

With the development and application of voltage source converter (VSC) high voltage direct current (HVDC) technology, DC distribution is gradually attracting the attention of researchers in recent years. However, many studies are still in the theoretical and exploratory stages. Compared with DC transmission networks, medium-voltage DC (MVDC) distribution networks are more sophisticated with respect to the complex operation modes, high penetration of renewable energy resource, and use of diverse power electronic devices. Therefore, master-slave control strategy which has been widely used in HVDC transmission projects may not be the first choice for DC distribution networks. In this study, a three-terminal DC distribution dynamic simulation platform is initially established and droop control strategy is adopted due to its flexible scalability. Secondly, plug and play solutions for key equipment such as VSCs and DC solid-state transformers are proposed. Thirdly, the response characteristics of a droop control system under high renewable energy resource penetration and frequent transition of operation mode are studied. Fourthly, the system fault isolation and recovery strategy under DC pole-to-pole fault is proposed. Finally, the whole control scheme is validated through experiments using the dynamic simulation platform. In the future, this proposed scheme can be used in the control of VSC-based MVDC distribution networks.