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Research Of High Efficiency Isolated High Step-up Converter

Posted on:2017-07-19Degree:MasterType:Thesis
Country:ChinaCandidate:B QianFull Text:PDF
GTID:2322330509962861Subject:Power electronics and electric drive
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.As a type of converter which can realize the function of DC boost, isolated high step-up converter will continue playing an important role in the field of new energy, aeronautics and astronautics. Currently, the research about isolated high step-up converter is mainly focused on three points, step-up ratio, efficiency and power density.This paper analyzed current research status about the high step-up converter, and introduced the commonly used way of voltage raising. Through comparing the typical isolated high step-up converters, advantages of the Forward-Flyback converter in the topology structure, switch stress and efficiency are illustrated. Finally, we take Forward-Flyback converter as our key research object.Forward-Flyback has three working mode: CCM, CRM and DCM. This paper analyzed the operating principle in detail, and introduced the way about how to implement CRM mode.Active clamp Forward-Flyback converter has two driving methods: complementary driving method and noncomplementary driving method. By analyzing, we finally chose the noncomplementary driving method which not only has short on-time and small circuiting current, but also is good for soft switching.In Forward-Flyback converter, there are three conventional control methods: off-time control, constant frequency control and quasi resonant control. Through comparing these three methods, we finally proposed a new hybrid control method. which is better to improve the efficiency in the full load range. The new method can be described as following: at heavy load, the converter operates in quasi resonant control method, at light load, the converter works in off-time control method, and at extremely light load, the converter runs in constant control method.The ac resistor of the transformer has direct relationship with the winding method and winding selection. In this paper, we chose the sandwich winding method, and we split the primary winding to several layers to interleave with the secondary winding.The parameter design results of Forward-Flyback are given in this paper, and a 300 W prototype is built to verify the validity of the new control strategy. By using the new hybrid control method, Forward-Flyback converter can realize soft switching in full input range and full load range. The peak efficiency of the entire converter is 97.66%, the CEC nominal average efficiency is 97.29%, and the CEC weighted efficiency is 97.19%.
Keywords/Search Tags:high efficiency, high step-up, Forward-Flyback, noncomplementary, hybrid control
PDF Full Text Request
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