Conditions on Optimum Percentage of Second-order Harmonic Circulating Current Injection Based on MMC

Modular Multilevel Converter Based High Voltage Direct Current has been paid wide attention and engineering application due to its technological advantages and shares great development prosperity. The analysis and solution to solve the suppression of the capacitance voltage fluctuation is the key part to determine operating properties of MMC. This paper firstly analyzes the structure of MMC based on its working principle, and the principle of capacitance voltage fluctuation of MMC. Then the paper comes up with the derived model of the capacitance voltage fluctuation based on modulation ratio in order to realize the control of capacitance voltage fluctuation control by modulation ratio control. Finally, after conducting research on the relationship between the capacitance voltage fluctuation, modulation ratio and the optimum percentage of second-order circulating current injection, this paper comes up with the optimum application condition when the second-order circulating current should be injected or isolated to best suppress the capacitance voltage fluctuation and bridge arm current respectively under sine wave modulation and three-order harmonic wave modulation.