Compound type high-voltage direct current transmission system

The invention provides a compound type high-voltage direct current transmission system which comprises at least one rectifier station, a contravariant station and an aerial electric power transmission line. The rectifier station and the contravariant station both comprise positive electrodes and negative electrodes, a thyristor current converter is adopted in the rectifier station, a positive electrode and a negative electrode of the thyristor current converter both comprise at least one twelve-impulse thyristor current converter, a voltage source current converter which has direct current fault processing capacity is adopted in the contravariant station, and a positive electrode and a negative electrode of voltage source current converter both comprise at least one multi-level current converter with two series-wound modules. Connection points of the positive electrodes and negative electrodes of each station are connected with a grounding electrode or a local network according to operation mode, a double electrode ground return wire or a single ground return wire or a single electrode metal return wire, of the direct current transmission system. By means of the compound type high-voltage direct current transmission system, a commutation failure of the contravariant station in the direct current transmission system is avoided, operation mode is flexible, reliability is high, and project cost is reduced. Besides, the advantages of the thyristor current converter and the voltage source current converter are integrated, and thus the compound type high-voltage direct current transmission system has direct current side fault processing capacity.