Research On The Technology Of Converter With Variable Turn Ratios

With the growth of energy consumption around the world, new energy has been widely used in various occasions, including aerospace power generation system, distributed power generation system, independent power generation system and so on. And the output voltage of new energy mostly changed in a wide range, so the converter, which can adapt to the wide input voltage and work well in the wide range, is particularly needed. A new technology of converter with variable turn ratios is proposed in this paper. Just a few devices are added to broaden the subject range of input voltage, and meanwhile it is easy to optimize the efficiency, stress, ripple, etc. In addition, it is easier to control the added devices.Firstly, the converter with variable turn ratios is constructed by adding a few devices on the seconday side of the basic phase shift full bridge converter(PSFBC), and its turn ratio is changed according to different input voltage. The relations between turn ratio and strss, soft switching, efficiency are studied in detail; the parameters of the proposed converter system are designed, and different turn ratios are choosed; according to analyzing various closed-loop control strategy, the PI control strategy of voltage closed-loop based on the analog chip UCC3895 is adopted finally; The simulation software Saber is used to accomplish simulation verification of the proposed converter, and a 1000 W prototype is also established. Simulation and experiment results all verify the correctness of theoretical analysis and the feasibility of the variable turn ratios technology.Secondly, the active clamp forward converter(ACFC) is chooesd as the basic topology of variable turn ratios technology again. After analyzing the characteristics of ACFC detailly, the scheme of variable turn ratios is proposed, and the parameters of the converter system including different turn ratios are all designed; the PI control strategy of voltage closed-loop based on the digital chip DSP28335, which is different from the analog control strategy of the phase shift full bridge converter with variable turn ratios, is adopted in the proposed ACFC system, and the theory of digital PI control strategy is analyzed detailly; the system is simulated by Saber, and a 500 W prototype is also established to accomplish experimental verification, which verify the correctness of theory. It is concluded that the variable turn ratios technology can be used to combine with most isolated converters and it is plastic, so it can be as an independent method to realize wide-range input.Finnaly, the stability of two proposed converters are analyzed. The mathematic models of two proposed converters are eatablished based on the small-signal model of Buck converter. Accoring to the mathematic models, the open-loop transfer functions of the continuous system of PSFBC with variable turn ratios and the discrete system of ACFC with variable turn ratios are built respectively, and then the bode diagrams are draw by using the Matlab. From the diagrams, the system stability is analyzed and verified.