Operation and control of hybrid HVDC system with LCC and full‐bridge MMC connected in parallel

In this study, a new kind of hybrid high‐voltage direct current (HVDC) system is proposed. Each terminal of the proposed system consists of one line commutated converter (LCC) and one full‐bridge modular multilevel converter (FB‐MMC). The LCC and FB‐MMC are connected in parallel so that they can share the same transmission line. The active–reactive power capability of the hybrid HVDC system is extended compared with the conventional LCC‐HVDC system, and power reversal control without power interruption can be achieved by the coordination control of LCC and FB‐MMC. Besides, the proposed hybrid HVDC system is capable of handling DC fault, because both LCC and FB‐MMC have DC fault blocking capability. Moreover, the power rating of FB‐MMC can be designed to low value while keeping the bulk‐power transmission capability of LCC. A two‐terminal bipolar hybrid HVDC system is built in PSCAD/EMTDC. The simulation results verify the effectiveness and feasibility of the proposed hybrid topology and corresponding control strategies.