Research On Soft-Switching Two-Transistor Forward Converter

With the rapid development of power electronics technology, the design of various power systems tends to high reliability, high frequency, and miniaturization. Two-transistor forward converter has many significant advantages, such as low switch voltage stress, anti-bridge arm shoot-through, high reliability and simple structure. Two-transistor forward converter obtains widely applications in various power system, communication power supply, arc welding power source and computer power source. Soft-switching technology has such features that improving operating environment of power devices, improve running reliability of electronic devices, reducing switching losses of system and reduce size of converters. The soft-switching technology is extremely beneficial for high-frequency, miniaturization of the power design. Thus, soft-switching two-transistor forward converter is a research hotspot in recent years, plays an irreplaceable role in the development of switching power supply, so research for the converter has important significance.Based on the extensive research on soft-switching two-transistor forward converter, this thesis lists several typical soft-switching two-transistor forward converters and parallel two-transistor forward soft-switching converters. The soft-switching achieve conditions and the disadvantages of these converters are analyzed in this thesis. Besides, in this thesis, summarize and generalize the realization methods of soft-switching converter. The thesis focus on the output coupled inductor interleaved two-transistor forward converter proposed by Japanese scholars. Aiming at the main disadvantages in the converter, that coupled inductor ratio has larger impact on switch current stress and freewheeling diode voltage stress, propose a novel interleaved two-transistor forward soft-switching converter.Compared with the output coupled inductor interleaved two-transistor forward converter, the novel interleaved two-transistor forward soft-switching converter improves the secondary auxiliary circuit. The novel converter constitutes a new auxiliary circuit using coupled inductors, maintain capacitance and auxiliary diode. The converter uses phase shift control and achieves soft action of all switches. The design of the converter auxiliary circuit current has no additional impact on the voltage stress and current stress and can effectively reduce circulation loss. According to the equivalent circuit diagram of the different operating modes analyze the converter works principle. Besides, realization of soft-switching conditions, the impact of coupled inductor ratio on current stress and output characteristics of the converter are analyzed in this thesis. Finally, based on the theoretical analysis, used Cadence 16.2 simulation platform to build a 500W/100kHz simulation model.The simulation results are given to verify the feasibility and correctness of the theoretical analysis and confirm the superior performance of the converter.