Research Of Soft-switching Design In High Step-up DC/DC Converter

Nowadays, high step-up DC/DC converter is playing an important role in field of power electronics. Usually, there needs to be a front-end high step-up DC/DC converter in PV system or portable AC power system. It will boost the low input DC voltage to the voltage high enough so that the inverter can send the generated power into the grid or the inverter can generate regular AC voltage. There are many researchers focusing on the topology of the high step-up DC/DC converter. Active-clamping and resonance technology is utilized to achieve high efficiency of the converter. However, there is no detailed research on resonance and soft switching design of these converters.This paper focuses on the soft switching design of high step-up DC/DC converter. A summary of soft switching design of previous topologies and modeling of resonance are presented. Furthermore, a novel method of soft switching design is proposed.Firstly, analysis and summary of ways to achieve soft switching in previous high step-up DC/DC topologies are presented. They are classified as primary-dominant resonance and secondary-dominant resonance. Resonance interval is analyzed and a modeling of resonance interval is obtained. Some contradictions between soft switching are pointed out and the design of an optimized resonance between primary-dominant resonance and secondary-dominant resonance is proposed. A prototype is implemented for validation.Secondly, a novel method of soft switching design based on forward-flyback topology is proposed. Reverse magnetizing current is used to obtain ZVS on of main MOSFET and resonance is utilized to obtain ZCS off of secondary diode. Seperated ways to realize two kinds of soft switching are utilized so that the contradiction is solved and the converter can obtain both two kinds of soft switching. Therefore, the converter gains better soft switching performance. Validation based on the prototype is made as well.Finally, an improved design of traditional push-pull converter in vehicle inverter system is proposed. A voltage doubler structure with resonance is designed on secondary side. The improved topology not only realizes ZCS off of secondary diodes but also achieves higher voltage gain so that the turn ratio of transformer is decreased. Experimental results validate its high efficiency.The topic of soft switching design is inevitable for high efficiency of high step-up DC/DC converter. The summary, modeling and design method in this paper are of certain importance and value. It is hoped that this paper can provide some proposals to engineers.