Abstract：Cascade and neutral-point-clamped (NPC) converter have become increasingly popular in recent years due to their practicability. This paper presents an improved hybrid cascade multilevel converter that is derived from these two topologies. The proposed converter is the series-connection of a diode-clamp converter and several H-bridge converters with the 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 this method, 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.
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2011, Vol. 26 
