A Capacitor Voltage Balancing Control Strategy for Modular Multilevel Converter

Abstract

Modular multilevel converter (MMC) is a promising highly modular converter. However, the problems of voltage balancing control strategies in the MMC should be studied in detail. In order to improve the effect of voltage balancing, reduce the amount of calculation, and simplify the switch control of the submodules (SMs), this paper proposes a method that using a matrix to control the switch signals of the SMs based on the nearest level control (NLC) method. First, by sorting the capacitor voltage of the SMs, the required SMs are selected according to the NLC method. Since each arm contains N SMs, it is assumed that each SM corresponds to an N-dimensional column vector. The nth element of column vector corresponding to the nth SM is 1, and the others are 0. Then, the column vectors corresponding to all the SMs are used to form an N × N identity matrix. Secondly, assuming that the identity matrix is E, when the i-th SM is selected, a column vector corresponding to it is selected, such as a(i)= E(:, i), where E(:, i) is the i -th column of E; then, the sum of a(i) is calculated to obtain the switch signals of all SMs of each arm, so as to control the SMs. Finally, the simulation was set up on the Matlab/Simulink, and the proposed method is studied and analyzed.