With the development of the flexible DC transmission techniques

the lightweight requirements of the converter valves have become increasingly urgent. The reduction of sub-module capacitance is difficult because of the requirements of the ripple amplitude of capacitor voltage

which is one of the key factors that affect the light weight of the valve. According to the characteristic that the fundamental frequency and second harmonic frequency components are the critical factors for voltage ripples

a novel strategy is proposed to reduce the voltage ripples of sub-module capacitor by controlling the reactance value of the bridge arm. The bridge arm reactor switching circuit and switching control strategy are designed. The proposed strategy and the existing circulating current suppression control(CCSC)strategies are researched in terms of mathematical principles. A two-terminal DC transmission model is built in PSCAD/EMTDC simulation environment

and the effectiveness of the proposed strategy is verified. Finally

the proposed strategy is compared with the CCSC strategy in the economic aspect and it is concluded that the proposed strategy has good economic performance.