Design of an improved modular multilevel converter reconfigurable equalization scheme based on difference of voltage variation

Abstract In order to solve the problem of lower available capacity and shorter cycle life due to the barrel effect of series-connected batteries, as well as the problem of pseudo-equalization caused by battery aging, this paper proposes a modified modular multilevel converter (MMC) reconfigurable equalization scheme with difference of voltage variation (DOVV) as the equalization variable. The equalization topology consists of an MMC circuit and a voltage regulator, which effectively solves the problems of low total available capacity, inefficient energy transfer, and slow equalization by reducing the number of switches and achieving independent control of the equalization and voltage regulator modules. A control strategy based on the Oxford aging dataset is proposed with DOVV as the equalization variable, and a fuzzy logic control algorithm is introduced according to the distribution characteristics of DOVV data. This equalization control strategy overcomes the pseudo-equalization phenomenon due to battery aging. The simulation results show that compared with the traditional DC–DC energy transfer equalization topology, the energy transfer efficiency of the proposed equalization topology is improved by 62.15% and the equalization time is reduced by about 16.36%, and the pseudo-equalization phenomenon caused by the aging of the battery pack during the equalization process is well overcome. The feasibility of the proposed equalization scheme is verified.