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The widespread use of renewable energy resources brings forth a requirement for high-power, high-efficiency, high-control-bandwidth grid-tied converters. This paper proposes a three-level active neutral-point-clamped zero-current-transition (3L-ANPC ZCT) converter for the sustainable energy power conversion systems. The proposed multilevel soft-switching topology can effectively increase efficiency and switching frequency of the systems by almost eliminating turn-OFF losses and greatly reducing turn-ON losses of semiconductor devices. The soft commutations of the main devices are achieved with simple auxiliary circuit of two auxiliary switches and one LC resonant tank for each phase leg as in the case of a two-level ZCT converter. The voltage rating of the auxiliary switches is the same as main switches, and is clamped to half of dc voltage, while the current rating is much smaller. Furthermore, the auxiliary switches switch under zero-current condition and have no switching losses. Compared with existing three-level diode neutral-point-clamped zero-current-transition (3L-DNPC ZCT) converter, the number of components in auxiliary circuit is halved, so the volume and cost are reduced. In addition, the deterioration of the soft commutation due to the parasitic inductances in the 3L-DNPC ZCT inverter does not exist in the proposed topology. The operation principle and comparison with the 3L-DNPC ZCT are analyzed in detail in this paper. Eighty kilowatt half-bridge prototypes of the 3L-ANPC ZCT converter and the 3L-DNPC ZCT converter are built and their circuit operation and analysis are experimentally verified.
Date of Publication: Dec. 2011