Spectral analysis of an improved hybrid cascade multilevel converter

This paper will present an improved cascade multilevel converter that is the series-connection of a diode-clamp converter and several H-bridge converters with equal dc bus voltage. According to this topology, a hybrid modulation method which incorporates square-wave synthesis in conjunction with unipolar triangle carried-based PWM method is illustrated. By the hybrid control scheme, higher voltage devices and faster devices can operate in synergism. Based on the anatomy of hybrid modulation process in nature, 3-D mathematic model is built. Further, by the double Fourier series expansion and intricate derivation, a rigorous output analytic solution is acquired, which facilitates the evaluation of spectra accurately. The feasibility and the advantages of the topology are validated by the experiment.