Generalization of a model-based controller for the N-Level cascaded H-Bridge multilevel converter used as a shunt active filter

The general function of the multilevel inverter is to synthesize a desired AC voltage from several levels of DC voltages. For this reason, multilevel converters are ideal for connecting either in series or in parallel an AC grid with renewable energy sources such as photovoltaics, fuel cells or with energy storage devices such as capacitors or batteries. For more levels of voltages, the total harmonic distortion of the voltage synthesized, decreases, but the control law gets complicated. This paper presents the modeling and control processes of the cascade H-bridge multilevel converter used as a shunt active filter. The single-phase five-level topology is firstly studied, then, is proposed the generalization of the model and the control law. The transformation of the model in terms of the sum and the difference of the squares of the capacitor voltages is crucial for our developments. Moreover, it is shown that, while the current tracking depends on the sum of the injected voltages, the balance of the capacitor voltages depends on the difference between them.