Research On Push Pull Forward Three Level DC/DC Converter

Fuel cell distributed generation has been attracting more and more attentions because of its high efficiency, free from contamination and flexible application scheme. The fuel cell is a kind of DC source, and the external characteristic curve is flexible. So the cascade organization of DC/DC and DC/AC is used in the fuel cell distributed generation. The DC/DC converts the low and wide range voltage to a high and steady one. As the mediate energy transfer, the performance of DC/DC converter is very important to the generation system. And it's very important to design the DC/DC converter.This paper reviews the development of the fuel cell distributed generation, lists the DC/DC converters which have already been used, and analyzes the advantages and disadvantages of them. Considering the characteristic of the fuel cell, this paper adopts the Push Pull Forward Three Level DC/DC Converter. The converter has the advantages including low voltage stress on the switches, low voltage stress on the rectifier diodes, small size of filter. And it is fit for the low, wide range voltage input, high voltage output occasions. The operating principle of the converter is analyzed, and the design method of a 1kW experimental prototype is given. The paper calculates the power losses of every part in main circuit of the converter, and gives four proposals to improve the efficiency of the converter.This paper establishes the small-signal modeling of the Push Pull Forward Three Level Converter. In order to achieve the output voltage regulation and the share of input capacitors'voltage, the paper uses a control strategy and designs the regulators. The output voltage loop has good stability and dynamic characteristics, the input capacitor voltage loop has good stability, and the two control are decoupled.At the end of the paper, the simulation results and experimental waveforms are shown, and verify the validity of the above analysis and design.