Research On Voltage Oscillation Reduction Method For Phase-Shift Full-Bridge ZVS Converter

Phase-Shift PWM ZVS full bridge converter is preferred in medium to high power conversionapplication. ZVS of primary switches can be achieved via the resonance between leakage inductanceof main transformer and parasitic capacitance of switches, which improves the conversion efficiency.However, the drawbacks of the conventional full bridge converter, like narrow ZVS range, large dutycycle loss, serious parasitic oscillation on rectifier, large circulating loss, limit its further application.Especially, the parasitic oscillation not only increases the voltage stress and conduction loss but alsointroduces serious electromagnetic interference. We apply full-bridge converter for application inmedium to high power conversion.Firstly, this paper presents a classification for soft switching technology and introduces theadvantages, disadvantages and research status of ZVS PWM full-bridge converter in detail. Based onthe drawback of the parasitic oscillation, this paper focuses on new methods to solve the problem.In the second chapter, the parasitic oscillation mechanism of full-bridge is investigated.Commutation principles of both leading-leg and lagging-leg are analyzed, so are the differences.Therefore, the new theory of super commutation to suppress secondary oscillation is proposed.A phase-shift full-bridge ZVS PWM converter with commutation capacitor and LC auxiliarycircuit is proposed in the third chapter. Since the rectifier commutates in advance, the voltageoscillation is reduced significantly, and there is no duty cycle loss. Meanwhile, this converter canachieve ZVS for all the switches over a wide load range by using the energy stored in the LC auxiliarycircuit and the filter inductor. The operation principle of this converter is discussed in detail anddesign method of key parameter is carefully depicted. Experimental results are given.Based on the drawbacks of the previous converter, a better one is proposed in which theintroduced auxiliary transformer forces the primary current commutating in advance. Parasitic voltageoscillation at secondary is well reduced. ZVS of primary switches can be achieved in much wide loadrange with the help of auxiliary coupled inductor, resulting in no circulating time, and ripple currentflowing through the output filter inductor decreases significantly. In this paper, performance of theproposed converter is verified with experimental results.The last chapter summarizes the major results of the work and offers suggestions for future work.