Improved Model Predictive Control of Three-level Voltage Source Converter

—In conventional model predictive control, 27 switching states for three-level power converters are evaluated online, and the state in which the cost function is the smallest will be applied in the next sampling period. The amount of calculation, however, is too high, and it may cause too high of a jump for the phase voltage or line voltage in the AC side of the three-level converter, which means that each switching action causes voltage variation to exceed Udc/2. To solve these problems, an improved model predictive method is proposed in this article. The proposed method only needs a subset of all the three-level states, which is obtained by adding and subtracting two-level state groups in the current switching state, for prediction and optimization. The high jump of the AC-side voltage is effectively avoided, and computational effort is greatly reduced. In addition, reduced switching frequency is obtained. The experiments are carried out by the two methods, and the results verify the correctness and feasibility of the proposed control strategy.