The modular multilevel converter(MMC)is being widely-used as the main topology of the voltage source converter based high voltage direct current transmission(VSC-HVDC)projects. The design of the main equipment parameters is of decisive significance

which is related to the investment and operation performance of the system. The main equipment parameters include the rated valve side no-load voltage of the coupling transformer

the leakage reactance of the coupling transformer

the arm inductance and the sub-module capacitance. Independent design of a single parameter leads to the neglect of the coupling characteristics between multiple parameters of different equipment. In this paper

the objective function and constraint equations are designed with an eye to multiple parameters of different equipment. And a nonlinear programming method is proposed to calculate these parameters. The nonlinear programming method takes into consideration the coupling characteristics between multiple parameters of different equipment. The integral algorithm proposed is implemented in the design of a MMC-HVDC project. Time-domain simulation studies based on PSCAD/EMTDC are performed to show that the calculation and simulation results with the method are basically consistent. This work is supported by National Natural Science Foundation of China(No. 51507060)and Fundamental Research Funds for the Central Universities(No. 2016MS07).