Research On High Step-Up Sepic Converter With Wide Input Voltage Range

In recent years,due to the increasing shortage of traditional fossil energy and the increasingly serious global environmental problems,the renewable and clean energy such as solar energy and full cell have draw a great attention in grid-connected generation and fuel cell vehicles.However,under the influence of climatic conditions,solar panels supply low and wide range of output voltage.In addition,the fuel cell has a “soft” output voltage characteristic.As the output current increases,the output voltage will drop,which results in wide output voltage range.In order to make the DC bus voltage of inverter maintain the requied and stable voltage when the low output voltage of solar panels and fuel cell changes,thus the boost DC/DC with a wide input voltage rang and high voltage gain is needed to act as required power interface between the new energy battery and dc bus for new energy generation and fuel cell vehicles.Firstly,various kinds of common DC/DC converters,which are currently used in fields of new energy generation and fuel cell vehicles,are briefly summarized.And an extendable voltage multiplier(VM)cells applied to SEPIC converter was proposed in this paper,the converter has some advantages such as high voltage gain,wide input voltage range,low voltage stress on switch and diodes,continuous and low ripple input current.At the same time,the proposed voltage multiplier cell does not contain active switches,so that the driver and control circuits of the SEPIC converter are adapted to proposed converter,no changes are needed.Beside,the topology can be extended according to the voltage gain requirement,thus the proposed converter can achieve higher voltage gain by adjusting the number of VM cells.Therefore,the proposed converter is suitable for the applications such as new energy generation and fuel cell vehicles.Secondly,the operating principles and performance characteristics of the proposed converter are analyzed,the theoretical calculation equations for the voltage gain and the stresses of all components are deduced.Then,the design processes of the devices parameters are given.The averaged switch method is adopted to model the converter in order to complete the design of control system loop compensation.A Psim simulation model is established to verify the feasibility of the proposed converter and the correctness of control strategy,and an experimental prototype with rated power of 300 W is built to verify proposed converter.The design process of hardware and software of the closed-loop control system is given.The main controller adopts TMS320F28335 and the control strategy is voltage-current dual loop control method.The hardware circuits and program design flow are given.The simulation and experimental results are consistent with the theoretical analysis,which verify the correctness of the proposed converter and effectiveness of control strategy.Finally,in order to reduce converter volume and improve system power density,a improved converter with lower voltage stress on capacitors is obtained by optimizing the topology of the aforementioned converter.Then the modified converter operates in a 1MHz frequency by utilizing Ga N device.As the switching frequency increases,the size of passive components reduces and the power density of switch-mode power supply improves.Based on the theoretical analysis,the main circuit and high frequency driver circuit of the improved converter are designed,and experimental prototype is built to verify the effectiveness of the proposed scheme.