A hybrid offshore wind farm direct current transmission converter, comprising: a diode rectifier, wherein an alternating current side of the diode rectifier is configured to be connected to a wind farm collection grid, and a direct current side of the diode rectifier is configured to be connected to a high-voltage direct current, HVDC, transmission line; and an auxiliary converter, wherein the auxiliary converter is connected in parallel to the diode rectifier such as to be connectable to the wind farm collection grid and the HVDC transmission line, wherein the auxiliary converter comprises: a modular multilevel converter, MMC, wherein an alternating current side of the MMC is connected to the wind farm collection grid via a transformer; and a submodule string, comprising a plurality of half-bridge submodules, wherein one end of the submodule string is connected to the MMC, and the other end is connected to the HVDC transmission line, characterized in that the other end is connected to the HVDC transmission line via a midpoint of an LC filter circuit, wherein the filter circuit is formed by a filter inductor and a filter capacitor, and the filter circuit is mounted on a direct current side of the auxiliary converter and is configured to prevent a high-frequency current inside the auxiliary converter from entering the HVDC transmission line, and wherein the filter capacitor is connected between an input end positive electrode and an input end negative electrode of the auxiliary converter. a diode rectifier, wherein an alternating current side of the diode rectifier is configured to be connected to a wind farm collection grid, and a direct current side of the diode rectifier is configured to be connected to a high-voltage direct current, HVDC, transmission line; and an auxiliary converter, wherein the auxiliary converter is connected in parallel to the diode rectifier such as to be connectable to the wind farm collection grid and the HVDC transmission line, wherein the auxiliary converter comprises: a modular multilevel converter, MMC, wherein an alternating current side of the MMC is connected to the wind farm collection grid via a transformer; and a submodule string, comprising a plurality of half-bridge submodules, wherein one end of the submodule string is connected to the MMC, and the other end is connected to the HVDC transmission line, characterized in that the other end is connected to the HVDC transmission line via a midpoint of an LC filter circuit, wherein the filter circuit is formed by a filter inductor and a filter capacitor, and the filter circuit is mounted on a direct current side of the auxiliary converter and is configured to prevent a high-frequency current inside the auxiliary converter from entering the HVDC transmission line, and wherein the filter capacitor is connected between an input end positive electrode and an input end negative electrode of the auxiliary converter. a modular multilevel converter, MMC, wherein an alternating current side of the MMC is connected to the wind farm collection grid via a transformer; and a submodule string, comprising a plurality of half-bridge submodules, wherein one end of the submodule string is connected to the MMC, and the other end is connected to the HVDC transmission line, characterized in that the other end is connected to the HVDC transmission line via a midpoint of an LC filter circuit, wherein the filter circuit is formed by a filter inductor and a filter capacitor, and the filter circuit is mounted on a direct current side of the auxiliary converter and is configured to prevent a high-frequency current inside the auxiliary converter from entering the HVDC transmission line, and wherein the filter capacitor is connected between an input end positive electrode and an input end negative electrode of the auxiliary converter.