Simplified Predictive Duty Cycle Control of Multilevel Converters With Internal Identical Structure

Classical finite control set model predictive control of multilevel converters faces two major limitations: heavy computation burden and low steady-state performance. On the other hand, the internal paralleled or cascaded identical structure is extensively employed in multilevel converters as the voltage level increases. Taking advantage of the internal identical structure in multilevel converters, a simplified predictive duty cycle control method for multilevel converters is proposed in this article. First, a series of switching pairs with the identical structure are modeled as a virtual switching state, and the number of the corresponding voltage vectors can be significantly reduced. Then, a least-square optimization problem is formulated to calculate the duty cycles for optimal output current tracking using these virtual voltage vectors. The output current quality is enhanced due to the employment of the interleaved output voltage stage with phase-shifted pulsewidth modulation. As the number of voltage vectors is significantly reduced, the computation burden is drastically reduced. The proposed method can be applied in various multilevel topologies with internal identical structures. Simulation and experimental results on the multilevel converters with internal cascaded/paralleled identical cells are presented to verify the good performance and application value of the proposed method.