Study On The Non-isolated Interleaved High Step-up DC/DC Converters

The non-isolated interleaved high step-up DC/DC converter has been widely usedin uninterrupted power supply system, electric vehicles, photovoltaic and fuel cell grid-connected system, and many other fields, but it needs high voltage gain and highefficiency.The conventional boost converter can achieve very high voltage gain with anextremely high duty cycle. In practice, however, it is difficult to design a boostconverter with very high voltage gain due to the equivalent series resistance(ESR) thatcauses poor efficiency and degrades the voltage gain.The optimized voltage gain of it islimited to approximately four times with a relative high efficiency.After summarizing the single-phase high step-up DC/DC converter, this paperfirstly studies and finds the regular topology structure.Based on the regular topologystructure, two high step-up boost converter based on topology combination areproposed, but they all work in hard switching state.In order to further improve theconverter efficiency, another two kinds of interleaved high step-up boost converter withsoft switching are presented.They take the variable frequency control to keep outputvoltage constant,it is bad for the design of filters.So, combining with the characteristicsof the converter gain, this paper adopts variable inductor control to overcome theoccurrence of the extreme duty cycle and the limits of the frequency control.This paperdevotes its efforts in the following aspects.Firstly, for improving the voltage gain of the boost converter, the three-teminalswitch-inductor network is took out to study.By putting proper polarity controlledvoltage source in three branches,there are many different structures,through analyzingand comparing their voltage gain and voltage stress, the optimal three-terminal networkis obtained.According to the optimal three-terminal network, a asymmetric interleavedhigh step-up boost converter based on topology combination is build.But it not good fornormalization design, based on the same principle, a symmetrical interleaved highstep-up boost converter based on topology combination is deduced. Their workingprinciple and performance characteristics are analyzed and verified by simulation.Secondly, because the above two interleaved high step-up boost converters workin hard switching state, a interleaved high step-up boost converter with soft switching ispresented. Anyway, it can achieve high gain by couple inductor, and all of its switchesand diodes work with soft switching.Besides, another similar performance converter can be get by the Y-Δ change of inductor. Under analyzing their working principle,these gains are deduced and soft switching conditions are achieved. Ultimately, anexperimental prototype of40W output power is constructed to verify the theoreticalanalysis.Finally, a variable inductor control is proposed to overcome the shortage of thetwo new soft switching converters taking frequency control in the secondly part.Theconverter with variable inductor control can adjust the inductor to control the outputvoltage constant under fixed duty radio and switching frequency.This paper introducesthe principle and detail design process of the variable inductor.The experimentalprototype is constructed to verify the theoretical analysis.