An analysis of combining dc circuit breaker and hybrid MMC with reduced number of FBSM for HVdc system protection

The hybrid modular multilevel converter (HMMC) is employing half-submodules (HBSMs) and full--bridge submodules (FBSMs), combining the advantages of both. Aiming to reduce the manufacture cost and power losses of such solution, this paper proposes an HMMC in combination with dc circuit breaker (CB) for MMC-based high-voltage direct current (HVdc) systems. Under such conditions, the characteristics of pole-to-pole permanent dc fault is analyzed. Simulation results considering a 150 MW/150 kV symmetrical monopole point-to-point MMC-based HVdc system demonstrate the effectiveness and feasibility of the proposed approach. In this way, the number of FBSM is reduced by about 60 % compared to typical HMMC solutions in the literature. Additionally, considering HMMC with dc CB solution, the peak value of dc fault current and the breaker voltage can be decreased by around 38 % and 50 %, respectively.