Coordinated fault ride-through strategy for DC faults of photovoltaic grid-connected MMC-HVDC systems

To cut fossil fuel use, using DC overhead line in large-scale photovoltaic (PV) grid-connected modular multilevel converter-high voltage direct current (MMC-HVDC) systems is a future trend. But DC overhead line short-circuit faults are likely and can damage devices. First, models for the system and PV station are set up in this paper. Second, for a large-capacity PV bipolar MMC-HVDC system, a unipolar short-circuit grounding fault of DC overhead line is analyzed. Finally, a coordinated DC fault ride-through control strategy considering direct current circuit breaker (DCCB), converter station control, and PV power output is proposed. When a fault occurs, the non-fault pole converter station keeps power transmission. The unbalanced power is calculated. By using PV array power output, the DC line voltage is optimized and PV power output reduced. To handle instantaneous failures, load reduction of PV station and converter station power feed-forward incremental control are proposed to maintain system power balance and grid connection stability. PSCAD/EMTDC simulation shows the method effectively maintains PV station and MMC-HVDC system operation and achieves fault ride-through.