The traditional nearest level modulation(NLM)has advantages of simple control and low switching fre-quency.However,when the number of output levels is small,the harmonic distortion rate of output waveform from a modular multilevel converter(MMC)under the NLM modulation will be large.In this paper,a full-bridge auxiliary sub-module is added to each arm of the traditional three-phase six-leg MMC topology,and the capacitance voltage of the auxiliary sub-module is half of that of the half-bridge sub-module.Aimed at this MMC topology,an improved hybrid modulation strategy is proposed,which can realize the balance control of half-bridge and auxiliary sub-module,reduce the harmonic distortion rate of MMC AC-side output current,and reduce the switching frequency and system loss of the full-bridge sub-module.A detailed simulation model is built in MATLAB/Simulink,and simulation results verify the effectiveness of the proposed MMC topology and the improved hybrid modulation strategy.
关键词
模块化多电平变流器/混合调制/平衡控制/降频控制
Key words
Modular multilevel converter(MMC)/hybrid modulation/balance control/frequency reduction control
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