| Modular Multilevel Converter (MMC) is topology suitable for high voltage, large power rate application, and is especially popular in High Voltage Direct Current transmission and motor drive. This paper focus on the Modular Multilevel Converter, introducing the advantages, development and the popular technologies of the converter, and do research on the following aspects:Firstly, the Carrier Phase Shifted modulation and the control schematic is introduced, under which the detail AC output, sub-module(SM) voltage balancing control, SM voltage averaging control mathematic model is deduced, at the same time, the designing of controller parameter is well analyzed. Simulations validate the correctness of the model and controller design.Secondly, aiming at the overlarge voltage fluctuation of the SM in low frequency working condition of motor driving, a new voltage suppression method is proposed based on careful analyzing the merits and defaults of existing control method, which is simple and effective. Simulations show the practicability of the proposed method.Lastly, the technical problems and tendency in the wind power generation is revealed, and the application advantages of modular multilevel converter is discussed. Based on the discussion, a back to back multilevel wind power generation converter (WPGC) is built in Matlab simulation, normal working conditions such as steady and dynamic state, MPPT control are carefully studied. Moreover, the low voltage ride through (LVRT) problem of the multilevel WPGC is discussed. A new protection method is proposed in the condition that all the available methods show unavoidable problem in the multilevel topology. Simulations testified the validity of the proposed method. |
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