Model predictive control of modular multilevel converter based on equivalent current decomposition model

Abstract

Due to its unique topology, modular multilevel converter (MMC) is very suitable for AC/AC conversion applications in distribution network and has broad development prospects. Aiming at the problems of multivariable coupling and multi-objective accurate control of single-phase direct AC/AC-MMC, a model predictive control (MPC) strategy based on current decomposition model is proposed in this paper. Firstly, according to the relationship between bridge arm electrical quantity and input and output, the equivalent current decomposition model of decoupling input circuit, output circuit and circulating circuit is derived. Then, the evaluation function with the output current, input current, circulating current and submodule (SM) capacitor voltage as the rolling optimization objective is established, the rolling optimization process of MPC is carried out according to the equivalent current model and simplified by selecting the optimal bridge arm levels, so as to realize the multi-objective accurate and fast control of AC/AC-MMC. Finally, the proposed MPC control strategy is simulated and compared with the traditional MPC control strategy and PI control strategy to verify the feasibility and effectiveness of the proposed control method.