Decentralized Controller for the Cell-Voltage Balancing of a Multilevel Flying Cap Converter

Inhalt:
This paper presents a decentralized method to balance the capacitor voltages of a Flying-Cap converter. In this study, a change of variable is proposed replacing the voltage of the capacitors by the cell-voltages to provide an appropriate model of the converter. The control strategy involves several cell-voltage-balancing local controllers associated to each cell and a global output current controller. The local controllers cancel the difference between their own local cell-voltage with the average value of the neighboring cell-voltages. Using this control method any number of cells constituting the converter can be handled. It provides also an auto-balancing property in case of an insertion or a removal of an active cell during operation, which can be useful to address fault-tolerant concerns. Furthermore, the study demonstrates that the dynamics of the two types of loops, the cell-voltage balancing and the output current regulation are uncorrelated. Simulations and experimental measurements validate the relevance of the proposed control method.