| In the face of the global shortage of energy resources and environmental degradation and other increasingly serious issues,the development and utilization of clean renewable energy such as solar energy,fuel cell,biomass energy has attracted worldwide attention.However,photovoltaic(PV)cell,fuel cell and other new energy storage devices exist such problems as low output voltage level and wide range fluctuation.Thus before these new energy storage devices were integrated into the grid,it is necessary to add high step-up DC-DC converter between their output and the input of the grid so that the output voltage level of the new energy storage devices can be improved to meet the requirements of the grid.Although the voltage gain of the traditional Boost converter can tend to infinity theoretically when the duty ratio D approaches to 1,it cannot obtain a high enough voltage gain due to the circuit device parasitic parameters and the influence of the control system,and even lead to the collapse of voltage gain and the converter cannot operate properly,thus it is generally suitable for applications where the voltage gain does not exceed four-time.It has become one of the hotpots of academic research that how to construct a DC/DC converter with higher voltage gain.In addition,due to the input current ripple of the high step-up DC/DC converter is large which can interfere the normal working and affects the service life of PV cell.Therefore,it is of great significance to study how to suppress the input current ripple.In response to above issues,the main contents of this thesis are shown as follow:? The existing non-isolated high step-up DC-DC converters and their respective advantages and disadvantages are summarized,then based on the high step-up DC/DC converter with coupled inductor,concerning how to improve the voltage gain,how to reduce switch loss and how to reduce switching device voltage stress,several high step-up DC/DC converter with coupled inductor are analyzed,and the topology construction rules and inner connection between them are clarified and revealed.? Based on the topology structure of traditional synchronous rectifier Boost converter,a general idea as ‘take a storage capacitor into the forward path of power transmission to obtain higher voltage gain while take an auxiliary current branch into the common point of the switch and the input inductor to realize soft switching of switches and ampere second balance of storage capacitor' has been proposed in this thesis.And according to this idea,a non-isolated high step-up ZVZCS DC-DC converters is constructed,and its voltage gain is twice that of traditional Boost converter,and the voltage stress of the switching device is reduced to 1/2 of that of the original Boost converter.? In order to saticify the requirement of input current ripple in PV power generation system,a non-isolated zero-ripple input current ZVZCS high step-up DC/DC converter is proposed by combing the proposed non-isolated ZVZCS high-gain dc converter with a passive ripple injection unit.This kind of converter not only retain the advantages of high voltage gain and soft switching of the original converter,but also realize the expected goal of zero-ripple input current by using the passive ripple injection unit to construct a ripple current with the same current ripple of theorginal converter.Finally,the correctness of the theoretical analysis is vertified by experiments.? In order to expand the application of the proposed high step-up DC/DC converter,a series of methods such as module integrated concept,circuit equivalent conversion principle and switch-capacitance booster technology are adopted,based on the proposed two kinds of non-isolated ZVZCS high-gain dc converter,a kinds of DC/DC converter with higher voltage gain are proposed: Modular parallel non-isolated ZVZCS high-gain DC/DC converter,floating-output non-isolated ZVZCS high step-up DC/DC converter and non-isolated zero-ripple input current ZVZCS high step-up DC/DC converter with switch-capacitor are proposed.According to the analysis of the working principle,performance and experiment validation among these three proposed high step-up DC/DC converter,it shows that these three proposed converter can effectively improve the voltage gain,reduces the voltage stress of the switch tube and diode,and suppresses the input current ripple.Furthermore,according to the idea of topological derivation,these three proposed high step-up DC/DC converter can satisfy different voltage gain applications by adjusting the number of modular or switch-capacitor units. |
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