Interline dc power flow controller with fault current-limiting capability

Power flow control and fault current limitation are two major problems that require an urgent solution in a direct current (dc) grid. This study proposes a novel interline dc power flow controller having a fault current limitation capability (FCL-PFC). The proposed controller is expected to realise overall control of the internal power flow in a dc grid and to limit the fault current under fault conditions. FCL-PFC exhibits small capacity and low loss and does not require energy from an alternating current (ac) system. The topological structure of FCL-PFC is first introduced. Then, the principles of power flow control and self-power balance using the dc voltage and ac circulating current, respectively, is discussed. The control strategy under stable conditions is further designed. Based on the proposed FCL-PFC action sequence under fault conditions, this study describes the calculation and analysis of the dc fault current in different periods for maximising the fault current limitation ability of FCL-PFC. Finally, a simulation model is used in PSCAD/EMTDC to verify the power flow control and fault current limitation capabilities of the proposed FCL-PFC. The economy of combining FCL-PFC with direct current circuit breakers is analysed.