Capacitor voltage balancing with switching sequence strategy for series-connected matrix-converter-based smart transformer

Series-connected Matrix-converter-based smart transformers (MCSTs) with capacitive voltage dividing networks are promising topologies owing to improvements in terms of reliability and power density. Well-known matrixconverter modulation techniques will lead to unbalances in capacitor voltages because a practical capacitive divider typically contains similar but not exactly equal capacitances. This article suggests a new capacitor voltage balancing control approach using carrier waveform offset shifting complemented by the appropriate semiconductor switching sequence to address capacitor voltages unbalance. As capacitor voltages are influenced by the switching sequence even in the theoretical case, where exactly equal capacitances are considered, improper switching sequences may lead to capacitor voltage unbalances. A thorough analysis is carried out based on the instantaneous capacitor currents in order to investigate the detailed influence on capacitor voltages. Proper switching sequences are devised together with the carrier offset. In order to verify the feasibility of the proposed topology as well as the correctness of the established model, simulations and hardware-in-loop experiments are carried out.