Load current corrected capacitor voltage control in eight-level DC-AC converter using extended commutation cells

The extended commutation cell is a four-port, four-switch cell that allows for bidirectional energy transport in two orthogonal directions throughout the cell. By cascading multiple cells a multilevel converter can be constructed with a high number of levels. The voltage across each cell capacitor can be adjusted independently of the load, resulting in high flexibility in output levels. This paper presents an improved method for capacitor voltage control, based on a system model and the measured output current. The proposed method is analyzed and verified on a 4.4 kW eight-level dc-ac converter. The obtained reduction in capacitor voltage ripple is more than 75%.