A seven-level converter using a combination of staircase and PWM switching methods

In this paper, a new method is proposed for switching a multilevel converter. In this converter two H-Bridge cells are connected in series with each phase of a three-phase diode-clamped converter. Operation of main converter and one of H-Bridge cells is based on the staircase switching method. Switching angles of the three phase converter and one of the H-Bridges are selected in a way to generate the fundamental harmonic of the phase and eliminate the fifth and seventh harmonics. However, the switching pattern of the second H-Bridge cell is based on PWM method. This cell generates the remaining parts of the desired sinusoidal waveform. Combination of these converters and their switching methods results in an output waveform with low harmonics. Simulation and experimental results agree with each other and show the proper operation of the proposed method.