The test platform of modular multilevel converter is an important means for the equivalent test of electrical stress test of power modules. In this paper

the generation mechanism of harmonic current is analyzed based on the topology and the modulation method. Then

the analytical expressions of the current ratio among the DC component

second harmonic

third harmonic and fundamental component by the fixed and average modulation are studied. At last

the harmonic current suppression method based on average modulation is proposed. The simulation platform in Matlab/Simulink is set up to compare and analyze the modelling accuracy and control performance of the two methods. The results show that the difference between the analytical expression and simulation results of the two methods is less than 7.9%

which verifies the correctness of the theoretical analysis. Compared with the fixed value method

the average value method can effectively reduce the second harmonic current by 50%

which verifies the effectiveness of the proposed method.