Research On ZVS Half-bridge Three-level DC/DC Converter With Two Clamping Diodes

The output voltage of the high power three-phase power factor correction (PFC) circuitis over800V, which makes the selection of the switches of the latter DC/DC convertersbecome difficult, while the three-level (TL) converter can solve the problem nicely. Thevoltage stress of TL converter is only the half of the input voltage. It is very suitable for theoccasions of high input voltage, middle/large power. Associating TL converter with softswitching could widen the application occasions for kinds of converters.Based on analysis of the merit and weak point of basic zero voltage switching (ZVS)half-bridge TL DC converter，the operation principle of the ZVS half-bridge TL DC converterwith two clamping diodes, the clamping function of the clamping diodes and two conditionsfor switches to achieve ZVS are analyzed in detail in this paper. A method using saturatedinductor instead of resonant inductor to reduce the duty loss effectively is presented in thispaper, and the principle and design of the saturated inductor are studied deeply. Based on theabove analysis, the parameter choice of the main components is discussed, especially thedesign and winding method of the transformer. Saber simulation analysis of the operationprinciples of main circuit is carried out. It can not only achieve ZVS for all switches, but alsodepress the voltage spike of the secondary rectifying diodes. Furthermore, it reduces the dutyloss faced by the conventional ZVS TL converters. Thus it has low loss, high efficiency andreferenced application value.A50kHz1.1KW (220V/5A) prototype with the controlling chip UC3875is implementedin the laboratory based on the proposed topology. The experimental results show that the ZVSTL converter is feasible in practical application. It testifies the validity of theory analysis.