Low-voltage-ride-through capability of an HVDC transmission system using two modular multilevel cascade converters (MMCC-DSCC)

This paper presents an intensive discussion on a long-distance high-voltage direct-current (HVDC) transmission system combining two modular multilevel cascade converters based on double-star chopper cells (MMCC-DSCC) with dc power cables. Hereinafter, a single MMCC-DSCC is referred to simply as a DSCC converter. HVDC transmission systems are required to provide low-voltage-ride-through (LVRT) capability to enhance availability. This paper proposes a new LVRT control method without any direct information exchange between the two DSCC converters. The validity of the control method is verified by simulated waveforms from the software package of PSCAD/EMTDC and experimental waveforms from a three-phase 200-V, 10-kW, 50-Hz downscaled HVDC system.