Research on shutdown control strategy of hybrid DC system

The hybrid DC system combined with line commutated converter (LCC) and hybrid modular multilevel converter (HY-MMC), which is named LCC-HY-MMC, has technical advantages and economy. Shutdown is a key problem that any DC system needs to face. In order to ensure that the DC system and the sub-module capacitors of HY-MMC can be discharged quickly during shutdown stage, a complete shutdown control strategy is proposed in this paper. From the characteristics of shutdown, it can be basically regarded as three stages: DC energy feedback stage, controllable dissipation stage of sub-module capacitor energy and uncontrollable dissipation stage of sub-module capacitor energy. Finally, based on the 200 MW/ 200 kV digital simulation model built in the electromagnetic transient simulation software PSCAD/EMTDC, the effectiveness of the proposed method is verified.