Additional direct-current voltage control method for modular multi-level current converter

The invention belongs to the technical field of operation and control of electric power systems and discloses an additional direct-current voltage control method for a modular multi-level current converter. The additional direct-current voltage control method comprises the steps that the minimum modulation ratio guaranteeing that the modular multi-level current converter outputs a full-level waveform is worked out; the current modulation ratio of the current converter is worked out according to the alternating-current voltage output by the converter and the direct-current voltage of the current converter; according to the minimum modulation ratio and the current modulation ratio of the current converter, the direct-current voltage adjustment amount delta Udc is determined; the current converter is controlled to output the real direct-current voltage with the value as delta Udc+Udc_ref. By the adoption of the additional direct-current voltage control method for the modular multi-level current converter, it can be guarnteed that each current converter keeps complete-level-number output, and a controller of each current converter can achieve the good control effect.