Exploiting the operational flexibility of AC-MTDC distribution system considering various flexible resources

•A novel economic and flexible dispatch of AC-MTDC distribution system is provided.•Power flow regulation of VSC and control mode switching of MTDC are incorporated.•Various flexible resources including CDGs, ESSs and flexible loads are considered.•Models of various flexible loads are given based on electricity characteristics.•Three flexibility indices are provided to evaluate system flexibility.•The proposed dispatching model takes flexibility constraints into account. Due to inherent volatility and uncertainty, the large-scale renewable energy integration has led to surge demands for operational flexibility in distribution system. Though various flexible resources in distribution system can help smooth the fluctuation of renewable energy, they also increase the complexity of dispatching. In order to enhance the flexibility of AC-MTDC distribution system, this paper proposes an economic and flexible scheduling model comprehensively considering source-grid-load-storage flexible resources, which exploits the potential flexibility by power flow controlling through VSC, control mode switching of MTDC and scheduling of flexible loads. Firstly, MTDC control strategy and mathematical models for various flexible resources are established. Then, the mechanism of flexibility supply–demand balance is analyzed, and three flexibility evaluation indices are presented from the perspective of flexibility supply–demand matching, network transmission flexibility and overall system flexibility respectively. Furthermore, a novel optimal scheduling model considering flexibility constraints is established to improve system flexibility. Finally, the proposed method is verified in a 47-bus AC-MTDC distribution network. Results show that the coordinated dispatching with power flow regulation, control mode switching of MTDC and flexible loads scheduling can greatly improve the flexibility of AC-MTDC distribution system and reduce the operation cost.