Design of Main Circuit Parameters for Modular Multilevel Matrix Converter in LFAC System

The low-frequency AC (LFAC) transmission is a competitive scheme for offshore wind power integration, in which the modular multilevel matrix converter ((MC)-C-3) is the key equipment. In this brief, the selection methods of the (MC)-C-3 main circuit parameters are proposed. First, the maximum arm voltage is derived and the selection method of the sub-module (SM) number is established. Then, according to the switching function approach, the analytical expressions of the average SM capacitor current and the average SM capacitor voltage are derived. On this basis, the selection method of the SM capacitance is proposed. Additionally, the design principle of the arm inductance is proposed. Finally, a case is elaborated to illustrate the proposed (MC)-C-3 main circuit parameter selection methods and provide a reference for practical projects.