An improved DC current flow controller with double quadrants operation and fault isolation capability. (December 2020) - Wang, Puyu
Abstract: The DC current flow controller (CFC) has capability of enhancing the control freedom of current/power flow in multi-terminal DC (MTDC) grids and solving the barrier of uncontrollability of DC branch currents. The control margins of the DC branch currents can be further improved if the power flow reversal is achieved with the DC CFC. An improved DC CFC (I-DCCFC) utilized in the meshed MTDC (M 2 TDC) grid is investigated with three contributions: (1) Regarding a traditional DC CFC (T-DCCFC), its operational mode and operating principle are analysed. The fact that T-DCCFC only has singular quadrant operation capability, which constrains the power flow reversal, is explained. (2) The I-DCCFC with double quadrants operation capability is presented. Its operating principle with power flow reversal capability is analysed. (3) Based on the control strategy of the T-DCCFC, the control strategy of the I-DCCFC is developed and the ability to isolate the DC fault is analysed. The simulation model of a three-terminal M 2 TDC grid with the I-DCCFC is established in PSCAD/EMTDC. The effectiveness of the I-DCCFC in controlling the DC branch currents with power flow reversal capability and fault isolation under the fault condition is verified by the simulation results. As the I-DCCFC inherits the modular design concept with strong scalability, it can be expanded into an improved multi-line DC CFC according to the actual demands.