Research On A Novel Asymmetrical Half-Bridge Soft-Switching DC/DC Converter

High freguency transformer isolated DC/DC converters specified for low voltage and high current output applications have been playing an important role for establishing more advanced power distribution system architectures in such as automotive and aero space electric power systems, as well as telecommunication and information equipments with energy storage systems. LLC series resonant converter is used in those situations mentiond above, which can achieve ZVS(Zero-Voltage-Switching, ZVS) in all its load range, but the PFM DC/DC converter has a shortcoming of severe audible noise generation in the low output power setting, and its output ripple current is higher in the high output current. Besides, IGBT(Insulated-Gate-Bipolar-Transistor, IGBT) is generally not suitable for the ZVS scheme because of the tail current transition at its turn-off commutation. As a solution for the soft switching limitations mentioned above, a new type of ZCS-PWM AHB(Asymmetrical Half-Bridge) DC/DC converter circuit topology based on IGBT for the low voltage/high current output, with wide range of the soft switching, has been proposed in this work.First of all, the theory of soft swiching and the development of the soft-switching DC/DC converter have been introduced. And then, by discussing the hard-switching half-bridge DC/DC converter, PWM asymetrical half-bridge DC/DC converter and LLC series resonant DC/DC conervter and summarizing their advantages and disadvantages, a novel lossless active snubbers-based Zero Current Switching(ZCS) PWM asymmetrical half-bridge converter with a low voltage/high current output characteristic is explored. By adopting the ZCS snubbers in the half-bridge DC/DC converter, both ZCS turn-on and ZVZCS turn-off soft switching commutation in the main and auxiliary switches can be realized without loss. As a result, zero current transition can be achieved in the wide range of output power setting under constant frequency PWM control strategy in the proposed DC/DC converter. In the third place, this thesis analyzed the soft-switching operation mechanism of the proposed topology in detail based on the equivalent circuit figures of different working modes, mathematical analyses of the dynamic process is also made. Besides, the design of the snubber and output voltage expression based on Fourier are also discussed. Simulation is made upon the principle analysis. The ZCS operation in the wide range of output power without loss which has solved the problem of tail current transition at IGBT’s turn-off commutation and the output characteristics are verified with simuliation results.Finally, a summary and analysis are made about the theoretical analysis, simulation research and possible problems of the converter proposed. Some outlook of the researching work is summarized as well.