DC and small-signal analysis, and design of a novel ZVZCS three-level converter with reduced rectifier voltage stress

A novel ZVZCS three-level PWM phase-shift controlled converter with regenerative passive snubber in the secondary is considered. The voltage stress on the rectifier diodes is reduced to n(V/sub in//2) (n is the transformer turns ratio) by using a few additional elements in the primary: two diodes, a small inductor and a small transformer winding. The conditions assuring ZVS of the leading leg and ZCS of the lagging leg are found as a function of the load current. Design constraints on the parallel capacitances of the switches of the leading leg, on the snubber's holding capacitor, and on the additional inductance and winding are hence established, allowing for an optimized knowledgeable design of the converter parameters. A DC analysis allows for the calculation of the effective duty-cycle. The DC characteristics of the proposed converter are found for different values of the duty-cycle. The boost effect on the effective duty-cycle due to the proposed snubber is proved. A small-signal model of the power stage and control-to-output transfer functions are derived, the damping effect of the proposed converter is compared to that of available soft-switching converters. Experiments on a prototype of 4.5 kW confirm the results.