A hybrid multilevel inverter with both staircase and PWM switching schemes

In this paper, a new method to control multilevel converters is proposed. The considered multilevel converter consists of a three-phase three-level diode-clamped converter (main converter). Two H-bridge cells are then connected in series with each output phase of the main converter. The operation of the main converter and one of the cascading Hbridge cells is based on the staircase switching method. The firing angles of these converters are selected in a way that the dc voltage required for the last H-bridge cell is minimized. The switching pattern of the second H-bridge cell is based on the pulse-width modulation method. This last cell generates the remaining parts of the desired sinusoidal output voltage. The combination of these converters and their switching methods result in an output waveform with low harmonics. Here, a fifteen-level converter is designed based on this approach. Simulation results and laboratory measurements verify the effectiveness of the proposed topology and modulation method.