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_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.