Improved Hybrid HVDC Circuit Breaker with Power Flow Control Capability for HVDC grids

Power flow control and DC fault protection are two major problems faced by high-voltage direct current (HVDC) grids. The modular multilevel power flow controller (MMPFC) has the bidirectional operation capability of both DC voltage and DC current, which meet the demand for the power flow control. The hybrid HVDC circuit breaker has the ultrafast DC current interruption capability. In this paper, based on the aforementioned equipment, an improved hybrid HVDC circuit breaker (IHCB) with power flow control capability is proposed. Firstly, the MMPFC and the hybrid HVDC circuit breaker are introduced, respectively. Secondly, the IHCB is proposed. In the IHCB, the load commutation switch (LCS) of the hybrid HVDC circuit breaker is replaced with the MMPFC. Then, detailed description of the control strategy for IHCB is illustrated. Finally, the case study is carried out based on PSCAD/EMTDC with a 4-terminal monopolar HVDC grid. The time-domain simulation results verified the performance and effectiveness of the proposed IHCB.