Specific sub-harmonic injection suppresses capacitor voltage fluctuation of modular multilevel converter

Suppressing capacitor voltage ripple of Modular multilevel converter (MMC) helps to reduce capacitor volume/weight and the cost of converter valve equipment. The ripple component and influence factors of the converter capacitor are deduced. The effects of the double frequency loop control and the third harmonic injection on the converter valve are analyzed. The proposed specific harmonic injection method can effectively reduce the capacitor voltage ripple of flexible DC converter valve (VSC), and the peak and RMS of arm current are controlled within the allowable range. The PSCAD simulation model was built based on zhangbei VSC engineering to verify the correctness and effectiveness of the proposed method.