The alternate arm converter(AAC)is one of the promising hybrid multi-level converters(HMCs)for high voltage direct current(HVDC)transmission over long-distance through high-capacity overhead lines(OHL). Firstly

the initial numbers of sub-modules in wave-shaping circuits and modules in the director switches are calculated to promise the steady-state operation and dc-fault blocking capability. Then the reliabilities of important devices are evaluated in terms of their electrical stresses

switch frequencies and actual structure. Furthermore

the redundant configuration method of wave-shaping circuits and director switches are proposed to sift the optimal redundant configuration

in which an objective function is established that reconciles reliability with investment in converters. Finally

the effectiveness of the proposed configuration strategy is verified by numerical calculation. This work is supported by State Grid Corporation of China(No. SGFJDK00DWJS1500031).