Control of hybrid modular multilevel converter based HVDC system under DC short circuit faults

摘要

Hybrid modular multi-level converter (Hybrid MMC) topology, consisting of both half-bridge (HB) and full-bridge (FB) submodules, is suitable for HVDC application as it combines the advantages of both HB-MMC and FB-MMC. This paper focuses on the control aspects of hybrid MMC with the objective of limiting DC fault current. It is also controlled to exchange reactive power with the AC grid during DC fault. Further, a negative sequence current injection method is proposed to eliminate the mismatch between the average capacitor voltages of the three legs of MMC appearing during DC faults. The proposed methods are tested through simulations in PSCAD/EMTDC platform.