D-q-DC reference frame control strategy for single-phase current source cascaded inverters

Power quality and reliability are inherent characteristics of the cascaded multilevel converters. However, in some converters, efforts should be made to ensure the durability and reliability of the equipment. This is the case of the single-phase current source cascaded inverter (SPCS-CI) in which, due to possible differences in the DC input current to each inverter of the system, it will be necessary to limit each output voltage of each unit. This can be done through a linear control strategy. In this work, the model and the mathematics of the problems caused by unbalanced DC currents in the described cascaded system are presented. Furthermore, a control scheme based on d-q reference frame components is proposed. Along with this, a control for the DC component voltages in the individual outputs of each inverter is added, which cannot be compensated completely by the d-q scheme. The proposed control strategy is a linear scheme with an updatable decoupler that allows to control d-q and DC voltages in a set of single-phase current source inverters disposed in a cascaded arrangement. Simulated results show the effectiveness of the proposed scheme.