Enlarged operational area of an Interline DC power Flow controller via adaptive droop control for Multi-Terminal HVDC systems

• Interline DC Power Flow Controller has some limitations which restrict its operation. The mentioned limitations are demonstrated and discussed. • An adaptive droop strategy is proposed which combines the IDC-PFC's operation to remove or mitigate the IDC-PFC's limitations. • The characteristics of the IDC-PFC with newly introduced degree of freedom (adaptive droop strategy) are extracted. The results exhibit extensions in IDC-PFC's operability. The effective performance of Interline DC Power Flow Controllers (IDC-PFCs) in Modular Multilevel Converters (MMC)-based High Voltage Direct Current (HVDC) grids is restricted by 1) the current limitation of the HVDC cables/lines, 2) the HVDC buses’ DC voltages and 3) the IDC-PFC capacitor’s DC voltage limit. The pivotal remedy for this issue is to utilize an adaptive droop control for the MMCs that varies its droop gain to maximize the IDC-PFC operation range. In this paper, 3D curves of the IDC-PFC’s important characteristics are used to assess the flexibility of the IDC-PFC control. By using this approach, a new degree of freedom for IDC-PFC controllability is achieved. The performance of the optimal-adaptive-droop-controlled strategy presented in this paper is validated using power flow studies. The results demonstrate that a wider operational area is conceivable for the IDC-PFC when this technique is applied as a combination of MMC converters’ droop control and IDC-PFC duty cycle.