In order to prevent the modular multilevel converter (MMC) internal circulation

an analysis is made of the voltage fluctuation and circulation generating mechanism of the MMC bridge arm

and a kind of compensation control method for circulation inhibition is proposed. When the MMC power exchange is in progress

the effect of bridge arm current causes the periodic change in the submodule capacitor voltage. It has found that submodule capacitor voltage contains DC component and AC component using the average value analysis method. For converter voltage modulation using the nearest level modulation method

it has been found that

as the submodule capacitor voltage contains DC component and fundamental component deviation

there exists fundamental frequency deviation and double frequency component between bridge arm voltage and the expected value

resulting in the circulation. By compensating for the bridge arm voltage and expected value deviation

it will be possible to eliminate bridge arm voltage deviation

thereby suppressing the circulation among the converter bridge arms. The 11-level MMC DC transmission system is set up in PSCAD/EMTDC

with the effectiveness of the method proposed verified by simulation results.