Interaction between inverters in the hybrid cascaded HVDC system under MMC converter transformer valve-side faults

• A valve-side single-phase-to-ground fault of the MMC converter transformer causes fault-induced inrush current. • Fault-induced inrush current causes voltage distortion on LCC inverter ac bus, leading to subsequent commutation failures. • Subsequent commutation failures aggravate the sympathetic inrush current caused by fault-induced inrush current. • Enhanced sympathetic inrush current causes the incorrect blocking of current differential protection. The scheme based on hybrid submodules against valve-side faults is adopted to mitigate fault-induced inrush current.