Research On High Gain Forward And Flyback Combined DC-DC Converter

In the new energy power generation system,due to the difference of photovoltaic modules and shadow effect,the output voltage varies widely,the voltage level is low,and the stability is poor,and the fuel cell is also faced with the same situation.In order to meet the level requirements of bus voltage on the input side of inverter in two-stage photovoltaic system,it is necessary to use DC-DC converter to boost DC voltage.Therefore,a new forward-flyback combined DC-DC converter is proposed from the aspects of high gain,wide range input,working mode and characteristics of the converter,and the corresponding theoretical analysis and experimental verification are carried out.The main research contents are as follows:First of all,a new forward-flyback combined DC-DC converter topology is constructed,which is suitable to be used as a front-stage DC-DC topology scheme in twostage photovoltaic system.The converter retains the original structure of the flyback topology,combines the forward and flyback output loops on the secondary side of the transformer,and divides the forward and flyback energy transmission loops with diodes.Among them,the flyback circuit is attached with an auxiliary clamp capacitor.Secondly,the modal analysis of the forward-flyback converter working in different modes is carried out,the relationship between voltage gain and inductor current is deduced,and the working characteristics of the circuit are further studied.The topology has the following remarkable advantages: the switch has energy transmission to the load side during turnon and turn-off,which improves the overall efficiency of the converter;compared with the traditional forward converter,it can adapt to the input voltage in a wider range and does not need additional magnetic reset circuit;compared with the flyback converter,it has higher input-output voltage ratio and smaller output current ripple,which further improves the power density.This paper also analyzes the energy transmission mode,circuit constraints and external characteristics of the converter under different operating modes,and then uses the Matlab/Simulink simulation software to build the forwardflyback combined DC-DC converter model,and the simulation results verify the correctness of the proposed topology theory analysis.Finally,the PWM control strategy is designed and the main circuit and control circuit are designed according to the characteristics of the converter,and the principle prototype platform is successfully built in the laboratory.When the converter is in 40V-60 VDC input,only a small duty cycle is needed to realize the 200VDC/200 W output.The experimental results show that the topology has high gain and is suitable for high voltage output.Figure [53] table [4] reference [85]...