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1、南京航空航天大学硕士学位论文小功率直直变换器研究姓名：丁秀华申请学位级别：硕士专业：电机与电器指导教师：龚春英20090101南京航空航天大学硕士学位论文 i 摘 要 大规模集成电路的出现，促进了电子设备的高功率密度化。这要求为之供电的直直变换器也随之高功率密度化。高频、高效开关变换是直直变换器实现高功率密度的基础。鉴于此，本文重点围绕高效率高功率密度小功率直直变换器的开发，尤其对高频下减小平面变压器绕组交流损耗布置技术、低压大电流输出场合同步整流技术和准谐振软开关技术开展研究。 一方面，磁性元件是决定变换器体积和重量的关键因素。提高工作频率，可以减少磁性元件的体积，但高频效应(包括集肤效应和
2、邻近效应)使绕组损耗增加。本文以减少绕组损耗为出发点，基于平面磁性元件的一维模型，分析了利用原副边绕组交叉换位技术减小反激式平面变压器绕组交流损耗的原理， 比较了不同工作模式 （DCM， CCM） 下绕组的交流损耗。 通过 Ansoft公司的 Maxwell 二维电磁场仿真软件进行了研究，并经过了实验验证。研究结果表明原副边绕组交叉换位结构可以显著减小多层并联绕组间的电流不均流程度，减小绕组损耗，提高变换器效率。 另一方面，对于低压大电流输出的直直变换器，副边整流二极管的压降成为了制约提高这种电路效率的瓶颈， 而低压大电流的 MOSFET 的导通电阻与肖特基二极管相比要低， 故采用导通电阻低的
3、 MOSFET 的同步整流技术得到了发展。同步整流技术的难点在于同步管的驱动设计。本文针对低压大电流输出的小功率直直变换器，围绕着变换器的效率问题，阐述了同步整流的原理和特点，并对现今同步整流驱动方案进行了比较，重点研究了电压型辅助绕组自驱动同步整流驱动方案和电流型能量回馈型同步整流驱动方案的工作原理和参数设计，成功地研制了一台 210W 基于电压型辅助绕组自驱动同步整流方案的双管反激直直变换器样机，较好地实现了高效率和高功率密度的要求。 工作频率的不断提升， 由于高频造成的开关管的开关损耗逐渐成了一个严重的问题。 对此，电源设计领域出现了软开关技术，即零电压开关和零电流开关。本文针对准谐振软
4、开关技术，研究了基于 Onsemi 公司 NCP1207 准谐振芯片的准谐振反激变换器，它的主要优点是利用开关管两端的电容与变压器原边的漏感产生的谐振，通过适当地控制实现了开关管在电压谷底时开通，减小了开关损耗，提高了变换器的效率。整个电路结构简单、满载效率高、空载损耗小。 关键词：直直变换器，平面变压器，同步整流，绕组交流损耗，交叉换位，准谐振，NCP1207 小功率直直变换器研究 ii Abstract The advent of large-scale integrated circuit has prompted the high power density of electronic
5、 equipments, which calls for the high power density of DC/DC converter. Nowadays, DC/DC converter with high power density continuously pays more and more attention on high frequency and high efficiency. Therefore, this thesis emphasized on the design of high efficient and high power density low powe
6、r DC/DC converter, especially the improvement of decreasing the winding loss of planar transformer under high frequency, synchronous rectification technique for low voltage, high current power supplies and quasi-resonant soft switching technique. On the one hand, magnetic components are the key fact
7、or which determine the size and weight of the converter. So it is essesntial to reduce the size of magnetic components. Increasing the working frequency can reduce the size of the magnetic components, however, the winding loss will increase when the frequency goes higher becauses of skin effect and
8、proximity effect. In order to reduce the winding loss, this thesis analyzes the principle of using interleaving techniques to decrease winding losses in flyback planar transformer, which is based on one-dimension model for winding of magnetic components. Furthermore, a comparative study of winding l
9、oss between continuous conduction mode(CCM) and discontinuous conduction mode(DCM) is carried out. The Ansoft Maxwell 2D electromagnetic field simulation software and experiments have been done. The results show that using interleaving techniques can greatly reduce winding losses due to the unequal
10、current distribution within parallel layers. On the other hand, the voltage drop of diode becomes the bottleneck of the improvements for low voltage and high current output DC/DC converters. To lower the severer rectification loss associated with low voltage and high current, synchronous rectifier(S
11、R) with lower on-resistance is commonly used to replace conventional schottky diode as rectification component. The major difficulty in synchronous rectification technique is the gate drive design. This article presents some research on the corresponding problem of high efficiency low voltage/high c
12、urrent output DC/DC converter. The principles and characteristics of synchronous rectification are given, and the design details of self-driven SR with auxiliary winding and current-driven SR with energy recovery from current sensing are analyzed. In this paper, a 210W dual-switch flyback converter
13、with auxiliary winding drive SR was successfully developed. The results show that high efficiency and high power density can be better realized in this prototype. 南京航空航天大学硕士学位论文 iii With the working frequency increasing, the switching losses gradually become a serious problem. To overcome this drawb
14、ack, the soft swtching techniques are taken into consideration. Either zero-voltage switching(ZVS) or zero-current switching(ZCS) operation thereby draws much attention in the power converters. This paper presents some research on quasi-resonant soft switch flyback converter. A novel flyback convert
15、er using quasi-resonant technology with NCP1207 is developed. When the converter operates in DCM, the switching can be turn on at quasi resonant valley by using the resonant between capacitor shunted to drain-source of switch and the leakage inductance of the transformer. In this paper, the principl
16、es and characteristics of quasi-resonant flyback converter are given. The circuit and method for determining the working frequency of this converter and the critical parameters are detailed. The experimental results show that the efficiency of converter can be improved with the approximate ZVS operation of the switch. The converter has many advantages, such as simple circuit structure, high efficiency at full load and low loss at no load. Keywords: DC/DC converter, Planar transformer, Synchron
