A Regenerative Cascaded Multilevel Converter Adopting Active Front Ends Only in Part of Cells

This paper studies a regenerative cascaded multilevel converter that substitutes active front ends for the diode-based front ends only in part of cells, and proposes a power tracking control strategy that does not need any motor parameters. During the induction motor´s deceleration, by controlling the two kinds of cells´ output voltages according to the motor´s power factor angle, the converter makes the motor-generated energy wholly collected by regenerative cells; thus, other cells´ dc-link voltages remain stable. Regeneration limitation is analyzed. The simulation results of a 6-kV six-cell cascaded converter and experiments on a laboratory cascaded converter verify that the converter can transfer the motor power back to the grid and allows the motor to decelerate more quickly. Moreover, the control strategy is suitable for the drive systems whose regenerated power cannot be estimated or is varying.