Model-based cascade control of single-phase Modular Multilevel Converters using ideal capacitor voltages reference

Electrical power conversions are common in a large variety of engineering applications. With reference to AC/DC and DC/AC power conversions, a strong research interest resides in multilevel converters, thanks to the many advantages they provide over standard two-level converters. In this paper, a power-oriented model of single-phase Modular Multilevel Converters (MMCs) is first provided, followed by a detailed harmonic analysis. The model is given in the form of a Power Oriented Graphs block scheme that can be directly implemented in the Matlab/Simulink environment. The performed harmonic analysis gives a deep and exact understanding of the different terms affecting the evolution of the voltage trajectories in the upper and lower arms of the converter. Next, a new model-based cascade control architecture for MMCs is proposed. Combined with the real-time calculation of the ideal average capacitor voltages reference, the proposed control architecture allows to properly track the desired load current while minimizing the tracking error and the harmonic content in the generated load current itself.