Taking parameters of a main circuit in a BBMC as optimization objects, and a total harmonic distortion of an output voltage of the BBMC, a deviation between an actual output current and a corresponding rated output current as optimization objectives, a mathematical model between optimization objects and optimization objectives is established. A multi-objective optimization satisfaction function and a multi-objective optimization fitness function are established by selecting a current rating as a rated output current of the BBMC. An adaptive wolf pack optimization algorithm is adopted to obtain a set of optimal parameters of the main circuit. The rated output current is changed to obtain n sets of optimal parameters, and functional relationships between the optimal parameters of the main circuit in the BBMC are obtained using a numerical fitting method. Optimal parameters of the main circuit corresponding to different current ratings are determined according to the functional relationships.